Seleziona il luogo attuale e mostra i dettagli su una mappa

Scopri come trovare la posizione attuale di un dispositivo Android e visualizzare i dettagli del luogo (un'attività commerciale o un altro punto d'interesse) in quella posizione. Segui questo tutorial per creare un'app per Android utilizzando l'SDK Maps per Android, l'SDK Places per Android e il fornitore di servizi di localizzazione nelle API di geolocalizzazione di Google Play Services.

Nota: questo tutorial richiede Google Play Services 11.2.0 o versioni successive.

Ottieni il codice

Clona o scarica il repository Samples dell'API Android di Google Maps v2 da GitHub.

Visualizza la versione Java dell'attività:

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    // Copyright 2020 Google LLC
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//      http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package com.example.currentplacedetailsonmap;

import android.content.DialogInterface;
import android.content.pm.PackageManager;
import android.location.Location;
import android.os.Bundle;

import android.util.Log;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.FrameLayout;
import android.widget.TextView;

import androidx.annotation.NonNull;
import androidx.appcompat.app.AlertDialog;
import androidx.appcompat.app.AppCompatActivity;
import androidx.core.app.ActivityCompat;
import androidx.core.content.ContextCompat;

import com.google.android.gms.location.FusedLocationProviderClient;
import com.google.android.gms.location.LocationServices;
import com.google.android.gms.maps.CameraUpdateFactory;
import com.google.android.gms.maps.GoogleMap;
import com.google.android.gms.maps.OnMapReadyCallback;
import com.google.android.gms.maps.SupportMapFragment;
import com.google.android.gms.maps.model.CameraPosition;
import com.google.android.gms.maps.model.LatLng;
import com.google.android.gms.maps.model.Marker;
import com.google.android.gms.maps.model.MarkerOptions;
import com.google.android.gms.tasks.OnCompleteListener;
import com.google.android.gms.tasks.Task;

import com.google.android.libraries.places.api.Places;
import com.google.android.libraries.places.api.model.Place;
import com.google.android.libraries.places.api.model.PlaceLikelihood;
import com.google.android.libraries.places.api.net.FindCurrentPlaceRequest;
import com.google.android.libraries.places.api.net.FindCurrentPlaceResponse;
import com.google.android.libraries.places.api.net.PlacesClient;

import java.util.Arrays;
import java.util.List;

/**
 * An activity that displays a map showing the place at the device's current location.
 */
public class MapsActivityCurrentPlace extends AppCompatActivity
        implements OnMapReadyCallback {

    private static final String TAG = MapsActivityCurrentPlace.class.getSimpleName();
    private GoogleMap map;
    private CameraPosition cameraPosition;

    // The entry point to the Places API.
    private PlacesClient placesClient;

    // The entry point to the Fused Location Provider.
    private FusedLocationProviderClient fusedLocationProviderClient;

    // A default location (Sydney, Australia) and default zoom to use when location permission is
    // not granted.
    private final LatLng defaultLocation = new LatLng(-33.8523341, 151.2106085);
    private static final int DEFAULT_ZOOM = 15;
    private static final int PERMISSIONS_REQUEST_ACCESS_FINE_LOCATION = 1;
    private boolean locationPermissionGranted;

    // The geographical location where the device is currently located. That is, the last-known
    // location retrieved by the Fused Location Provider.
    private Location lastKnownLocation;

    // Keys for storing activity state.
    private static final String KEY_CAMERA_POSITION = "camera_position";
    private static final String KEY_LOCATION = "location";

    // Used for selecting the current place.
    private static final int M_MAX_ENTRIES = 5;
    private String[] likelyPlaceNames;
    private String[] likelyPlaceAddresses;
    private List[] likelyPlaceAttributions;
    private LatLng[] likelyPlaceLatLngs;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        // Retrieve location and camera position from saved instance state.
        if (savedInstanceState != null) {
            lastKnownLocation = savedInstanceState.getParcelable(KEY_LOCATION);
            cameraPosition = savedInstanceState.getParcelable(KEY_CAMERA_POSITION);
        }

        // Retrieve the content view that renders the map.
        setContentView(R.layout.activity_maps);

        // Construct a PlacesClient
        Places.initialize(getApplicationContext(), BuildConfig.PLACES_API_KEY);
        placesClient = Places.createClient(this);

        // Construct a FusedLocationProviderClient.
        fusedLocationProviderClient = LocationServices.getFusedLocationProviderClient(this);

        // Build the map.
        SupportMapFragment mapFragment = (SupportMapFragment) getSupportFragmentManager()
                .findFragmentById(R.id.map);
        mapFragment.getMapAsync(this);
    }

    /**
     * Saves the state of the map when the activity is paused.
     */
    @Override
    protected void onSaveInstanceState(Bundle outState) {
        if (map != null) {
            outState.putParcelable(KEY_CAMERA_POSITION, map.getCameraPosition());
            outState.putParcelable(KEY_LOCATION, lastKnownLocation);
        }
        super.onSaveInstanceState(outState);
    }

    /**
     * Sets up the options menu.
     * @param menu The options menu.
     * @return Boolean.
     */
    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        getMenuInflater().inflate(R.menu.current_place_menu, menu);
        return true;
    }

    /**
     * Handles a click on the menu option to get a place.
     * @param item The menu item to handle.
     * @return Boolean.
     */
    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        if (item.getItemId() == R.id.option_get_place) {
            showCurrentPlace();
        }
        return true;
    }

    /**
     * Manipulates the map when it's available.
     * This callback is triggered when the map is ready to be used.
     */
    @Override
    public void onMapReady(GoogleMap map) {
        this.map = map;

        // Use a custom info window adapter to handle multiple lines of text in the
        // info window contents.
        this.map.setInfoWindowAdapter(new GoogleMap.InfoWindowAdapter() {

            @Override
            // Return null here, so that getInfoContents() is called next.
            public View getInfoWindow(Marker arg0) {
                return null;
            }

            @Override
            public View getInfoContents(Marker marker) {
                // Inflate the layouts for the info window, title and snippet.
                View infoWindow = getLayoutInflater().inflate(R.layout.custom_info_contents,
                        (FrameLayout) findViewById(R.id.map), false);

                TextView title = infoWindow.findViewById(R.id.title);
                title.setText(marker.getTitle());

                TextView snippet = infoWindow.findViewById(R.id.snippet);
                snippet.setText(marker.getSnippet());

                return infoWindow;
            }
        });

        // Prompt the user for permission.
        getLocationPermission();

        // Turn on the My Location layer and the related control on the map.
        updateLocationUI();

        // Get the current location of the device and set the position of the map.
        getDeviceLocation();
    }

    /**
     * Gets the current location of the device, and positions the map's camera.
     */
    private void getDeviceLocation() {
        /*
         * Get the best and most recent location of the device, which may be null in rare
         * cases when a location is not available.
         */
        try {
            if (locationPermissionGranted) {
                Task<Location> locationResult = fusedLocationProviderClient.getLastLocation();
                locationResult.addOnCompleteListener(this, new OnCompleteListener<Location>() {
                    @Override
                    public void onComplete(@NonNull Task<Location> task) {
                        if (task.isSuccessful()) {
                            // Set the map's camera position to the current location of the device.
                            lastKnownLocation = task.getResult();
                            if (lastKnownLocation != null) {
                                map.moveCamera(CameraUpdateFactory.newLatLngZoom(
                                        new LatLng(lastKnownLocation.getLatitude(),
                                                lastKnownLocation.getLongitude()), DEFAULT_ZOOM));
                            }
                        } else {
                            Log.d(TAG, "Current location is null. Using defaults.");
                            Log.e(TAG, "Exception: %s", task.getException());
                            map.moveCamera(CameraUpdateFactory
                                    .newLatLngZoom(defaultLocation, DEFAULT_ZOOM));
                            map.getUiSettings().setMyLocationButtonEnabled(false);
                        }
                    }
                });
            }
        } catch (SecurityException e)  {
            Log.e("Exception: %s", e.getMessage(), e);
        }
    }

    /**
     * Prompts the user for permission to use the device location.
     */
    private void getLocationPermission() {
        /*
         * Request location permission, so that we can get the location of the
         * device. The result of the permission request is handled by a callback,
         * onRequestPermissionsResult.
         */
        if (ContextCompat.checkSelfPermission(this.getApplicationContext(),
                android.Manifest.permission.ACCESS_FINE_LOCATION)
                == PackageManager.PERMISSION_GRANTED) {
            locationPermissionGranted = true;
        } else {
            ActivityCompat.requestPermissions(this,
                    new String[]{android.Manifest.permission.ACCESS_FINE_LOCATION},
                    PERMISSIONS_REQUEST_ACCESS_FINE_LOCATION);
        }
    }

    /**
     * Handles the result of the request for location permissions.
     */
    @Override
    public void onRequestPermissionsResult(int requestCode,
                                           @NonNull String[] permissions,
                                           @NonNull int[] grantResults) {
        locationPermissionGranted = false;
        if (requestCode
            == PERMISSIONS_REQUEST_ACCESS_FINE_LOCATION) {// If request is cancelled, the result arrays are empty.
            if (grantResults.length > 0
                && grantResults[0] == PackageManager.PERMISSION_GRANTED) {
                locationPermissionGranted = true;
            }
        } else {
            super.onRequestPermissionsResult(requestCode, permissions, grantResults);
        }
        updateLocationUI();
    }

    /**
     * Prompts the user to select the current place from a list of likely places, and shows the
     * current place on the map - provided the user has granted location permission.
     */
    private void showCurrentPlace() {
        if (map == null) {
            return;
        }

        if (locationPermissionGranted) {
            // Use fields to define the data types to return.
            List<Place.Field> placeFields = Arrays.asList(Place.Field.NAME, Place.Field.ADDRESS,
                    Place.Field.LAT_LNG);

            // Use the builder to create a FindCurrentPlaceRequest.
            FindCurrentPlaceRequest request =
                    FindCurrentPlaceRequest.newInstance(placeFields);

            // Get the likely places - that is, the businesses and other points of interest that
            // are the best match for the device's current location.
            @SuppressWarnings("MissingPermission") final
            Task<FindCurrentPlaceResponse> placeResult =
                    placesClient.findCurrentPlace(request);
            placeResult.addOnCompleteListener (new OnCompleteListener<FindCurrentPlaceResponse>() {
                @Override
                public void onComplete(@NonNull Task<FindCurrentPlaceResponse> task) {
                    if (task.isSuccessful() && task.getResult() != null) {
                        FindCurrentPlaceResponse likelyPlaces = task.getResult();

                        // Set the count, handling cases where less than 5 entries are returned.
                        int count;
                        if (likelyPlaces.getPlaceLikelihoods().size() < M_MAX_ENTRIES) {
                            count = likelyPlaces.getPlaceLikelihoods().size();
                        } else {
                            count = M_MAX_ENTRIES;
                        }

                        int i = 0;
                        likelyPlaceNames = new String[count];
                        likelyPlaceAddresses = new String[count];
                        likelyPlaceAttributions = new List[count];
                        likelyPlaceLatLngs = new LatLng[count];

                        for (PlaceLikelihood placeLikelihood : likelyPlaces.getPlaceLikelihoods()) {
                            // Build a list of likely places to show the user.
                            likelyPlaceNames[i] = placeLikelihood.getPlace().getName();
                            likelyPlaceAddresses[i] = placeLikelihood.getPlace().getAddress();
                            likelyPlaceAttributions[i] = placeLikelihood.getPlace()
                                    .getAttributions();
                            likelyPlaceLatLngs[i] = placeLikelihood.getPlace().getLatLng();

                            i++;
                            if (i > (count - 1)) {
                                break;
                            }
                        }

                        // Show a dialog offering the user the list of likely places, and add a
                        // marker at the selected place.
                        MapsActivityCurrentPlace.this.openPlacesDialog();
                    }
                    else {
                        Log.e(TAG, "Exception: %s", task.getException());
                    }
                }
            });
        } else {
            // The user has not granted permission.
            Log.i(TAG, "The user did not grant location permission.");

            // Add a default marker, because the user hasn't selected a place.
            map.addMarker(new MarkerOptions()
                    .title(getString(R.string.default_info_title))
                    .position(defaultLocation)
                    .snippet(getString(R.string.default_info_snippet)));

            // Prompt the user for permission.
            getLocationPermission();
        }
    }

    /**
     * Displays a form allowing the user to select a place from a list of likely places.
     */
    private void openPlacesDialog() {
        // Ask the user to choose the place where they are now.
        DialogInterface.OnClickListener listener = new DialogInterface.OnClickListener() {
            @Override
            public void onClick(DialogInterface dialog, int which) {
                // The "which" argument contains the position of the selected item.
                LatLng markerLatLng = likelyPlaceLatLngs[which];
                String markerSnippet = likelyPlaceAddresses[which];
                if (likelyPlaceAttributions[which] != null) {
                    markerSnippet = markerSnippet + "\n" + likelyPlaceAttributions[which];
                }

                // Add a marker for the selected place, with an info window
                // showing information about that place.
                map.addMarker(new MarkerOptions()
                        .title(likelyPlaceNames[which])
                        .position(markerLatLng)
                        .snippet(markerSnippet));

                // Position the map's camera at the location of the marker.
                map.moveCamera(CameraUpdateFactory.newLatLngZoom(markerLatLng,
                        DEFAULT_ZOOM));
            }
        };

        // Display the dialog.
        AlertDialog dialog = new AlertDialog.Builder(this)
                .setTitle(R.string.pick_place)
                .setItems(likelyPlaceNames, listener)
                .show();
    }

    /**
     * Updates the map's UI settings based on whether the user has granted location permission.
     */
    private void updateLocationUI() {
        if (map == null) {
            return;
        }
        try {
            if (locationPermissionGranted) {
                map.setMyLocationEnabled(true);
                map.getUiSettings().setMyLocationButtonEnabled(true);
            } else {
                map.setMyLocationEnabled(false);
                map.getUiSettings().setMyLocationButtonEnabled(false);
                lastKnownLocation = null;
                getLocationPermission();
            }
        } catch (SecurityException e)  {
            Log.e("Exception: %s", e.getMessage());
        }
    }
}

    

Visualizza la versione Kotlin dell'attività:

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    // Copyright 2020 Google LLC
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//      http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package com.example.currentplacedetailsonmap

import android.Manifest
import android.annotation.SuppressLint
import android.content.DialogInterface
import android.content.pm.PackageManager
import android.location.Location
import android.os.Bundle
import android.util.Log
import android.view.Menu
import android.view.MenuItem
import android.view.View
import android.widget.FrameLayout
import android.widget.TextView
import androidx.appcompat.app.AlertDialog
import androidx.appcompat.app.AppCompatActivity
import androidx.core.app.ActivityCompat
import androidx.core.content.ContextCompat
import com.google.android.gms.location.FusedLocationProviderClient
import com.google.android.gms.location.LocationServices
import com.google.android.gms.maps.CameraUpdateFactory
import com.google.android.gms.maps.GoogleMap
import com.google.android.gms.maps.GoogleMap.InfoWindowAdapter
import com.google.android.gms.maps.OnMapReadyCallback
import com.google.android.gms.maps.SupportMapFragment
import com.google.android.gms.maps.model.CameraPosition
import com.google.android.gms.maps.model.LatLng
import com.google.android.gms.maps.model.Marker
import com.google.android.gms.maps.model.MarkerOptions
import com.google.android.libraries.places.api.Places
import com.google.android.libraries.places.api.model.Place
import com.google.android.libraries.places.api.net.FindCurrentPlaceRequest
import com.google.android.libraries.places.api.net.PlacesClient

/**
 * An activity that displays a map showing the place at the device's current location.
 */
class MapsActivityCurrentPlace : AppCompatActivity(), OnMapReadyCallback {
    private var map: GoogleMap? = null
    private var cameraPosition: CameraPosition? = null

    // The entry point to the Places API.
    private lateinit var placesClient: PlacesClient

    // The entry point to the Fused Location Provider.
    private lateinit var fusedLocationProviderClient: FusedLocationProviderClient

    // A default location (Sydney, Australia) and default zoom to use when location permission is
    // not granted.
    private val defaultLocation = LatLng(-33.8523341, 151.2106085)
    private var locationPermissionGranted = false

    // The geographical location where the device is currently located. That is, the last-known
    // location retrieved by the Fused Location Provider.
    private var lastKnownLocation: Location? = null
    private var likelyPlaceNames: Array<String?> = arrayOfNulls(0)
    private var likelyPlaceAddresses: Array<String?> = arrayOfNulls(0)
    private var likelyPlaceAttributions: Array<List<*>?> = arrayOfNulls(0)
    private var likelyPlaceLatLngs: Array<LatLng?> = arrayOfNulls(0)

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)

        // Retrieve location and camera position from saved instance state.
        if (savedInstanceState != null) {
            lastKnownLocation = savedInstanceState.getParcelable(KEY_LOCATION)
            cameraPosition = savedInstanceState.getParcelable(KEY_CAMERA_POSITION)
        }

        // Retrieve the content view that renders the map.
        setContentView(R.layout.activity_maps)

        // Construct a PlacesClient
        Places.initialize(applicationContext, BuildConfig.MAPS_API_KEY)
        placesClient = Places.createClient(this)

        // Construct a FusedLocationProviderClient.
        fusedLocationProviderClient = LocationServices.getFusedLocationProviderClient(this)

        // Build the map.
        val mapFragment = supportFragmentManager
            .findFragmentById(R.id.map) as SupportMapFragment?
        mapFragment?.getMapAsync(this)
    }

    /**
     * Saves the state of the map when the activity is paused.
     */
    override fun onSaveInstanceState(outState: Bundle) {
        map?.let { map ->
            outState.putParcelable(KEY_CAMERA_POSITION, map.cameraPosition)
            outState.putParcelable(KEY_LOCATION, lastKnownLocation)
        }
        super.onSaveInstanceState(outState)
    }

    /**
     * Sets up the options menu.
     * @param menu The options menu.
     * @return Boolean.
     */
    override fun onCreateOptionsMenu(menu: Menu): Boolean {
        menuInflater.inflate(R.menu.current_place_menu, menu)
        return true
    }

    /**
     * Handles a click on the menu option to get a place.
     * @param item The menu item to handle.
     * @return Boolean.
     */
    override fun onOptionsItemSelected(item: MenuItem): Boolean {
        if (item.itemId == R.id.option_get_place) {
            showCurrentPlace()
        }
        return true
    }

    /**
     * Manipulates the map when it's available.
     * This callback is triggered when the map is ready to be used.
     */
    override fun onMapReady(map: GoogleMap) {
        this.map = map

        // Use a custom info window adapter to handle multiple lines of text in the
        // info window contents.
        this.map?.setInfoWindowAdapter(object : InfoWindowAdapter {
            // Return null here, so that getInfoContents() is called next.
            override fun getInfoWindow(arg0: Marker): View? {
                return null
            }

            override fun getInfoContents(marker: Marker): View {
                // Inflate the layouts for the info window, title and snippet.
                val infoWindow = layoutInflater.inflate(R.layout.custom_info_contents,
                    findViewById<FrameLayout>(R.id.map), false)
                val title = infoWindow.findViewById<TextView>(R.id.title)
                title.text = marker.title
                val snippet = infoWindow.findViewById<TextView>(R.id.snippet)
                snippet.text = marker.snippet
                return infoWindow
            }
        })

        // Prompt the user for permission.
        getLocationPermission()

        // Turn on the My Location layer and the related control on the map.
        updateLocationUI()

        // Get the current location of the device and set the position of the map.
        getDeviceLocation()
    }

    /**
     * Gets the current location of the device, and positions the map's camera.
     */
    @SuppressLint("MissingPermission")
    private fun getDeviceLocation() {
        /*
         * Get the best and most recent location of the device, which may be null in rare
         * cases when a location is not available.
         */
        try {
            if (locationPermissionGranted) {
                val locationResult = fusedLocationProviderClient.lastLocation
                locationResult.addOnCompleteListener(this) { task ->
                    if (task.isSuccessful) {
                        // Set the map's camera position to the current location of the device.
                        lastKnownLocation = task.result
                        if (lastKnownLocation != null) {
                            map?.moveCamera(CameraUpdateFactory.newLatLngZoom(
                                LatLng(lastKnownLocation!!.latitude,
                                    lastKnownLocation!!.longitude), DEFAULT_ZOOM.toFloat()))
                        }
                    } else {
                        Log.d(TAG, "Current location is null. Using defaults.")
                        Log.e(TAG, "Exception: %s", task.exception)
                        map?.moveCamera(CameraUpdateFactory
                            .newLatLngZoom(defaultLocation, DEFAULT_ZOOM.toFloat()))
                        map?.uiSettings?.isMyLocationButtonEnabled = false
                    }
                }
            }
        } catch (e: SecurityException) {
            Log.e("Exception: %s", e.message, e)
        }
    }

    /**
     * Prompts the user for permission to use the device location.
     */
    private fun getLocationPermission() {
        /*
         * Request location permission, so that we can get the location of the
         * device. The result of the permission request is handled by a callback,
         * onRequestPermissionsResult.
         */
        if (ContextCompat.checkSelfPermission(this.applicationContext,
                Manifest.permission.ACCESS_FINE_LOCATION)
            == PackageManager.PERMISSION_GRANTED) {
            locationPermissionGranted = true
        } else {
            ActivityCompat.requestPermissions(this, arrayOf(Manifest.permission.ACCESS_FINE_LOCATION),
                PERMISSIONS_REQUEST_ACCESS_FINE_LOCATION)
        }
    }

    /**
     * Handles the result of the request for location permissions.
     */
    override fun onRequestPermissionsResult(requestCode: Int,
                                            permissions: Array<String>,
                                            grantResults: IntArray) {
        locationPermissionGranted = false
        when (requestCode) {
            PERMISSIONS_REQUEST_ACCESS_FINE_LOCATION -> {

                // If request is cancelled, the result arrays are empty.
                if (grantResults.isNotEmpty() &&
                    grantResults[0] == PackageManager.PERMISSION_GRANTED) {
                    locationPermissionGranted = true
                }
            }
            else -> super.onRequestPermissionsResult(requestCode, permissions, grantResults)
        }
        updateLocationUI()
    }

    /**
     * Prompts the user to select the current place from a list of likely places, and shows the
     * current place on the map - provided the user has granted location permission.
     */
    @SuppressLint("MissingPermission")
    private fun showCurrentPlace() {
        if (map == null) {
            return
        }
        if (locationPermissionGranted) {
            // Use fields to define the data types to return.
            val placeFields = listOf(Place.Field.NAME, Place.Field.ADDRESS, Place.Field.LAT_LNG)

            // Use the builder to create a FindCurrentPlaceRequest.
            val request = FindCurrentPlaceRequest.newInstance(placeFields)

            // Get the likely places - that is, the businesses and other points of interest that
            // are the best match for the device's current location.
            val placeResult = placesClient.findCurrentPlace(request)
            placeResult.addOnCompleteListener { task ->
                if (task.isSuccessful && task.result != null) {
                    val likelyPlaces = task.result

                    // Set the count, handling cases where less than 5 entries are returned.
                    val count = if (likelyPlaces != null && likelyPlaces.placeLikelihoods.size < M_MAX_ENTRIES) {
                        likelyPlaces.placeLikelihoods.size
                    } else {
                        M_MAX_ENTRIES
                    }
                    var i = 0
                    likelyPlaceNames = arrayOfNulls(count)
                    likelyPlaceAddresses = arrayOfNulls(count)
                    likelyPlaceAttributions = arrayOfNulls<List<*>?>(count)
                    likelyPlaceLatLngs = arrayOfNulls(count)
                    for (placeLikelihood in likelyPlaces?.placeLikelihoods ?: emptyList()) {
                        // Build a list of likely places to show the user.
                        likelyPlaceNames[i] = placeLikelihood.place.name
                        likelyPlaceAddresses[i] = placeLikelihood.place.address
                        likelyPlaceAttributions[i] = placeLikelihood.place.attributions
                        likelyPlaceLatLngs[i] = placeLikelihood.place.latLng
                        i++
                        if (i > count - 1) {
                            break
                        }
                    }

                    // Show a dialog offering the user the list of likely places, and add a
                    // marker at the selected place.
                    openPlacesDialog()
                } else {
                    Log.e(TAG, "Exception: %s", task.exception)
                }
            }
        } else {
            // The user has not granted permission.
            Log.i(TAG, "The user did not grant location permission.")

            // Add a default marker, because the user hasn't selected a place.
            map?.addMarker(MarkerOptions()
                .title(getString(R.string.default_info_title))
                .position(defaultLocation)
                .snippet(getString(R.string.default_info_snippet)))

            // Prompt the user for permission.
            getLocationPermission()
        }
    }

    /**
     * Displays a form allowing the user to select a place from a list of likely places.
     */
    private fun openPlacesDialog() {
        // Ask the user to choose the place where they are now.
        val listener = DialogInterface.OnClickListener { dialog, which -> // The "which" argument contains the position of the selected item.
            val markerLatLng = likelyPlaceLatLngs[which]
            var markerSnippet = likelyPlaceAddresses[which]
            if (likelyPlaceAttributions[which] != null) {
                markerSnippet = """
                    $markerSnippet
                    ${likelyPlaceAttributions[which]}
                    """.trimIndent()
            }

            if (markerLatLng == null) {
                return@OnClickListener
            }

            // Add a marker for the selected place, with an info window
            // showing information about that place.
            map?.addMarker(MarkerOptions()
                .title(likelyPlaceNames[which])
                .position(markerLatLng)
                .snippet(markerSnippet))

            // Position the map's camera at the location of the marker.
            map?.moveCamera(CameraUpdateFactory.newLatLngZoom(markerLatLng,
                DEFAULT_ZOOM.toFloat()))
        }

        // Display the dialog.
        AlertDialog.Builder(this)
            .setTitle(R.string.pick_place)
            .setItems(likelyPlaceNames, listener)
            .show()
    }

    /**
     * Updates the map's UI settings based on whether the user has granted location permission.
     */
    @SuppressLint("MissingPermission")
    private fun updateLocationUI() {
        if (map == null) {
            return
        }
        try {
            if (locationPermissionGranted) {
                map?.isMyLocationEnabled = true
                map?.uiSettings?.isMyLocationButtonEnabled = true
            } else {
                map?.isMyLocationEnabled = false
                map?.uiSettings?.isMyLocationButtonEnabled = false
                lastKnownLocation = null
                getLocationPermission()
            }
        } catch (e: SecurityException) {
            Log.e("Exception: %s", e.message, e)
        }
    }

    companion object {
        private val TAG = MapsActivityCurrentPlace::class.java.simpleName
        private const val DEFAULT_ZOOM = 15
        private const val PERMISSIONS_REQUEST_ACCESS_FINE_LOCATION = 1

        // Keys for storing activity state.
        private const val KEY_CAMERA_POSITION = "camera_position"
        private const val KEY_LOCATION = "location"

        // Used for selecting the current place.
        private const val M_MAX_ENTRIES = 5
    }
}

    

Configura il progetto di sviluppo

Segui questi passaggi per creare il progetto tutorial in Android Studio.

1. Scarica e installa Android Studio.
2. Aggiungi il pacchetto Google Play Services ad Android Studio.
3. Clona o scarica il repository Samples dell'API Android di Google Maps v2 se non l'hai fatto quando hai iniziato a leggere questo tutorial.

4. Importa il progetto del tutorial:

   • In Android Studio, seleziona File > Nuovo > Importa progetto.
   • Vai alla posizione in cui hai salvato il repository Samples dell'API Android di Google Maps v2 dopo averlo scaricato.
   • Trova il progetto CurrentPlaceDetailsOnMap in questa posizione:
     PATH-TO-SAVED-REPO/android-samples/tutorials/java/CurrentPlaceDetailsOnMap (Java) o
     PATH-TO-SAVED-REPO/android-samples/tutorials/kotlin/CurrentPlaceDetailsOnMap (Kotlin)
   • Seleziona la directory del progetto e fai clic su Apri. Android Studio ora crea il tuo progetto utilizzando lo strumento di creazione Gradle.

Abilita le API necessarie e ottieni una chiave API

Per completare questo tutorial, devi avere un progetto Google Cloud con le API necessarie abilitate e una chiave API autorizzata a utilizzare Maps SDK for Android. Per ulteriori dettagli, vedi:

• Configurare il progetto Google Cloud
• Utilizzare una chiave API

Nota: questo tutorial richiede l'attivazione dell'API Places e dell'SDK Maps for Android.

Per visualizzare le API abilitate, vai alla pagina Google Maps Platform nella console Cloud e seleziona il tuo progetto:

Vai alla pagina di Google Maps Platform

Se non vedi che l'API Places sia abilitata nel tuo progetto, devi abilitarla:

Abilita l'API Places

Se aggiungi restrizioni alla chiave API, assicurati di aggiungere l'API Places alla chiave. Per ulteriori informazioni, consulta Utilizzo delle chiavi API.

Aggiungi la chiave API all'app

1. Apri il file local.properties del progetto.

2. Aggiungi la stringa seguente, quindi sostituisci YOUR_API_KEY con il valore della tua chiave API:

   MAPS_API_KEY=YOUR_API_KEY

   Quando crei la tua app, il plug-in Secrets Gradle per Android copia la chiave API e la rende disponibile come variabile di build nel file manifest Android.

Crea ed esegui la tua app

1. Collega un dispositivo Android al computer. Segui le instructions per attivare le opzioni sviluppatore sul tuo dispositivo Android e configurare il sistema in modo da rilevare il dispositivo.

   In alternativa, puoi utilizzare Gestione dispositivi virtuali (AVD) Android per configurare un dispositivo virtuale. Quando scegli un emulatore, assicurati di scegliere un'immagine che includa le API di Google. Per maggiori dettagli, consulta la pagina Configurare un progetto Android Studio.

2. In Android Studio, fai clic sull'opzione di menu Esegui (o sull'icona del pulsante di riproduzione). Scegli un dispositivo come richiesto.

Android Studio richiama Gradle per creare l'app, quindi la esegue sul dispositivo o sull'emulatore. Dovresti visualizzare una mappa con una serie di indicatori centrati sulla tua posizione corrente, simili all'immagine in questa pagina.

1. Seleziona Trova luogo per aprire un elenco di luoghi (un'attività o un altro punto d'interesse) nelle vicinanze della tua posizione corrente.
2. Seleziona un luogo dall'elenco. Viene aggiunto un indicatore alla mappa per il luogo selezionato.

Risoluzione dei problemi:

• Se non visualizzi una mappa, verifica di aver ottenuto una chiave API e averla aggiunta all'app, come descritto sopra. Controlla il log in Android Monitor di Android Studio per eventuali messaggi di errore sulla chiave API.
• Se la mappa mostra un singolo indicatore sul Sydney Harbour Bridge (la posizione predefinita specificata nell'app), verifica di avere concesso l'autorizzazione di accesso alla posizione all'app. In fase di esecuzione, l'app richiede l'autorizzazione di accesso alla posizione, seguendo lo schema descritto nella guida alle autorizzazioni di Android. Tieni presente che puoi anche impostare le autorizzazioni direttamente sul dispositivo, scegliendo Impostazioni > App > nome app > Autorizzazioni > Posizione. Per maggiori dettagli su come gestire le autorizzazioni nel codice, consulta la guida riportata di seguito per richiedere l'autorizzazione di accesso alla posizione nell'app.
• Utilizza gli strumenti di debug di Android Studio per visualizzare i log ed eseguire il debug dell'app.

comprendi il codice

Questa parte del tutorial illustra le parti più significative dell'app CurrentPlaceDetailsOnMap per aiutarti a capire come creare un'app simile.

Crea l'istanza del client API Places

Questi oggetti sono i principali punti di ingresso a Places SDK for Android:

• La classe Places crea e gestisce i client per l'SDK Places for Android.
• L'interfaccia di PlacesClient recupera la posizione attuale del dispositivo e i luoghi vicini alla posizione.

L'interfaccia LocationServices è il punto di accesso principale per i servizi di geolocalizzazione di Android.

Per utilizzare le API, procedi nel seguente modo nel metodo onCreate() del frammento o dell'attività:

1. Inizializza un oggetto Places.
2. Crea un oggetto PlacesClient.
3. Crea un oggetto FusedLocationProviderClient.

Ad esempio:

Java

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    // ...

    // Retrieve the content view that renders the map.
    setContentView(R.layout.activity_maps);

    // Construct a PlacesClient
    Places.initialize(getApplicationContext(), getString(R.string.maps_api_key));
    placesClient = Places.createClient(this);

    // Construct a FusedLocationProviderClient.
    fusedLocationProviderClient = LocationServices.getFusedLocationProviderClient(this);
}

Kotlin

override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)

    // ...

    // Retrieve the content view that renders the map.
    setContentView(R.layout.activity_maps)

    // Construct a PlacesClient
    Places.initialize(applicationContext, getString(R.string.maps_api_key))
    placesClient = Places.createClient(this)

    // Construct a FusedLocationProviderClient.
    fusedLocationProviderClient = LocationServices.getFusedLocationProviderClient(this)

}

Richiedi autorizzazione di accesso alla posizione

L'app deve richiedere l'autorizzazione di accesso alla posizione per determinare la posizione del dispositivo e consentire all'utente di toccare il pulsante La mia posizione sulla mappa.

Questo tutorial fornisce il codice necessario per richiedere l'autorizzazione di accesso alla posizione precisa. Per maggiori dettagli, consulta la guida alle autorizzazioni Android.

1. Aggiungi l'autorizzazione come elemento secondario dell'elemento <manifest> nel file manifest Android:

   <manifest xmlns:android="http://schemas.android.com/apk/res/android"
       package="com.example.currentplacedetailsonmap">
       <uses-permission android:name="android.permission.ACCESS_FINE_LOCATION" />
   </manifest>
   

2. Richiedi le autorizzazioni di runtime nella tua app, offrendo all'utente la possibilità di consentire o negare l'autorizzazione di accesso alla posizione. Il codice seguente verifica se l'utente ha concesso l'autorizzazione di accesso alla posizione precisa. In caso contrario, richiede l'autorizzazione:

   Java

   private void getLocationPermission() {
       /*
        * Request location permission, so that we can get the location of the
        * device. The result of the permission request is handled by a callback,
        * onRequestPermissionsResult.
        */
       if (ContextCompat.checkSelfPermission(this.getApplicationContext(),
               android.Manifest.permission.ACCESS_FINE_LOCATION)
               == PackageManager.PERMISSION_GRANTED) {
           locationPermissionGranted = true;
       } else {
           ActivityCompat.requestPermissions(this,
                   new String[]{android.Manifest.permission.ACCESS_FINE_LOCATION},
                   PERMISSIONS_REQUEST_ACCESS_FINE_LOCATION);
       }
   }
   MapsActivityCurrentPlace.java
   

   Kotlin

   private fun getLocationPermission() {
       /*
        * Request location permission, so that we can get the location of the
        * device. The result of the permission request is handled by a callback,
        * onRequestPermissionsResult.
        */
       if (ContextCompat.checkSelfPermission(this.applicationContext,
               Manifest.permission.ACCESS_FINE_LOCATION)
           == PackageManager.PERMISSION_GRANTED) {
           locationPermissionGranted = true
       } else {
           ActivityCompat.requestPermissions(this, arrayOf(Manifest.permission.ACCESS_FINE_LOCATION),
               PERMISSIONS_REQUEST_ACCESS_FINE_LOCATION)
       }
   }
   MapsActivityCurrentPlace.kt
   

3. Esegui l'override del callback onRequestPermissionsResult() per gestire il risultato della richiesta di autorizzazione:

   Java

   @Override
   public void onRequestPermissionsResult(int requestCode,
                                          @NonNull String[] permissions,
                                          @NonNull int[] grantResults) {
       locationPermissionGranted = false;
       if (requestCode
           == PERMISSIONS_REQUEST_ACCESS_FINE_LOCATION) {// If request is cancelled, the result arrays are empty.
           if (grantResults.length > 0
               && grantResults[0] == PackageManager.PERMISSION_GRANTED) {
               locationPermissionGranted = true;
           }
       } else {
           super.onRequestPermissionsResult(requestCode, permissions, grantResults);
       }
       updateLocationUI();
   }
   MapsActivityCurrentPlace.java
   

   Kotlin

   override fun onRequestPermissionsResult(requestCode: Int,
                                           permissions: Array<String>,
                                           grantResults: IntArray) {
       locationPermissionGranted = false
       when (requestCode) {
           PERMISSIONS_REQUEST_ACCESS_FINE_LOCATION -> {
   
               // If request is cancelled, the result arrays are empty.
               if (grantResults.isNotEmpty() &&
                   grantResults[0] == PackageManager.PERMISSION_GRANTED) {
                   locationPermissionGranted = true
               }
           }
           else -> super.onRequestPermissionsResult(requestCode, permissions, grantResults)
       }
       updateLocationUI()
   }
   MapsActivityCurrentPlace.kt
   

   Una sezione successiva di questo tutorial descrive il metodo updateLocationUI().

Aggiungi una mappa

Visualizza una mappa utilizzando Maps SDK for Android.

1. Aggiungi un elemento <fragment> al file di layout della tua attività, activity_maps.xml. Questo elemento definisce un elemento SupportMapFragment che funge da contenitore per la mappa e fornisce l'accesso all'oggetto GoogleMap. Il tutorial utilizza la versione della libreria di supporto Android del frammento di mappa, per garantire la compatibilità con le versioni precedenti del framework Android.

   <!--
    Copyright 2020 Google LLC
   
    Licensed under the Apache License, Version 2.0 (the "License");
    you may not use this file except in compliance with the License.
    You may obtain a copy of the License at
   
         http://www.apache.org/licenses/LICENSE-2.0
   
    Unless required by applicable law or agreed to in writing, software
    distributed under the License is distributed on an "AS IS" BASIS,
    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    See the License for the specific language governing permissions and
    limitations under the License.
   -->
   
   <fragment xmlns:android="http://schemas.android.com/apk/res/android"
       xmlns:tools="http://schemas.android.com/tools"
       android:id="@+id/map"
       android:name="com.google.android.gms.maps.SupportMapFragment"
       android:layout_width="match_parent"
       android:layout_height="match_parent"
       tools:context="com.example.currentplacedetailsonmap.MapsActivityCurrentPlace" />
   
   

2. Nel metodo onCreate() dell'attività, imposta il file di layout come visualizzazione dei contenuti:

   Java

   @Override
   protected void onCreate(Bundle savedInstanceState) {
       super.onCreate(savedInstanceState);
   
   
       // Retrieve the content view that renders the map.
       setContentView(R.layout.activity_maps);
   
   }
   MapsActivityCurrentPlace.java
   

   Kotlin

   override fun onCreate(savedInstanceState: Bundle?) {
       super.onCreate(savedInstanceState)
   
   
       // Retrieve the content view that renders the map.
       setContentView(R.layout.activity_maps)
   
   }
   MapsActivityCurrentPlace.kt
   

3. Implementa l'interfaccia OnMapReadyCallback e sostituisci il metodo onMapReady(), per configurare la mappa quando l'oggetto GoogleMap è disponibile:

   Java

   @Override
   public void onMapReady(GoogleMap map) {
       this.map = map;
   
       // ...
   
       // Turn on the My Location layer and the related control on the map.
       updateLocationUI();
   
       // Get the current location of the device and set the position of the map.
       getDeviceLocation();
   }
   MapsActivityCurrentPlace.java
   

   Kotlin

   override fun onMapReady(map: GoogleMap) {
       this.map = map
   
       // ...
   
       // Turn on the My Location layer and the related control on the map.
       updateLocationUI()
   
       // Get the current location of the device and set the position of the map.
       getDeviceLocation()
   }
   MapsActivityCurrentPlace.kt
   

4. Nel metodo onCreate() dell'attività, ottieni un handle per il frammento di mappa chiamando FragmentManager.findFragmentById(). Quindi utilizza getMapAsync() per registrarti al callback della mappa:

   Java

   SupportMapFragment mapFragment = (SupportMapFragment) getSupportFragmentManager()
           .findFragmentById(R.id.map);
   mapFragment.getMapAsync(this);
   MapsActivityCurrentPlace.java
   

   Kotlin

   val mapFragment = supportFragmentManager
       .findFragmentById(R.id.map) as SupportMapFragment?
   mapFragment?.getMapAsync(this)
   MapsActivityCurrentPlace.kt
   

5. Scrivi un metodo updateLocationUI() per impostare i controlli della posizione sulla mappa. Se l'utente ha concesso l'autorizzazione di accesso alla posizione, attiva il livello La mia posizione e il relativo controllo sulla mappa. In caso contrario, disabilita il livello e il controllo e imposta la posizione corrente su null:

   Java

   private void updateLocationUI() {
       if (map == null) {
           return;
       }
       try {
           if (locationPermissionGranted) {
               map.setMyLocationEnabled(true);
               map.getUiSettings().setMyLocationButtonEnabled(true);
           } else {
               map.setMyLocationEnabled(false);
               map.getUiSettings().setMyLocationButtonEnabled(false);
               lastKnownLocation = null;
               getLocationPermission();
           }
       } catch (SecurityException e)  {
           Log.e("Exception: %s", e.getMessage());
       }
   }
   MapsActivityCurrentPlace.java
   

   Kotlin

   @SuppressLint("MissingPermission")
   private fun updateLocationUI() {
       if (map == null) {
           return
       }
       try {
           if (locationPermissionGranted) {
               map?.isMyLocationEnabled = true
               map?.uiSettings?.isMyLocationButtonEnabled = true
           } else {
               map?.isMyLocationEnabled = false
               map?.uiSettings?.isMyLocationButtonEnabled = false
               lastKnownLocation = null
               getLocationPermission()
           }
       } catch (e: SecurityException) {
           Log.e("Exception: %s", e.message, e)
       }
   }
   MapsActivityCurrentPlace.kt
   

Ottenere la posizione del dispositivo Android e posizionare la mappa

Utilizza il fornitore della posizione incorporata per trovare l'ultima posizione nota del dispositivo, quindi utilizza questa posizione per posizionare la mappa. Il tutorial fornisce il codice necessario. Per maggiori dettagli su come ottenere la posizione del dispositivo, consulta la guida del fornitore di servizi di geolocalizzazione con fusibile nelle API di geolocalizzazione di Google Play Services.

Java

private void getDeviceLocation() {
    /*
     * Get the best and most recent location of the device, which may be null in rare
     * cases when a location is not available.
     */
    try {
        if (locationPermissionGranted) {
            Task<Location> locationResult = fusedLocationProviderClient.getLastLocation();
            locationResult.addOnCompleteListener(this, new OnCompleteListener<Location>() {
                @Override
                public void onComplete(@NonNull Task<Location> task) {
                    if (task.isSuccessful()) {
                        // Set the map's camera position to the current location of the device.
                        lastKnownLocation = task.getResult();
                        if (lastKnownLocation != null) {
                            map.moveCamera(CameraUpdateFactory.newLatLngZoom(
                                    new LatLng(lastKnownLocation.getLatitude(),
                                            lastKnownLocation.getLongitude()), DEFAULT_ZOOM));
                        }
                    } else {
                        Log.d(TAG, "Current location is null. Using defaults.");
                        Log.e(TAG, "Exception: %s", task.getException());
                        map.moveCamera(CameraUpdateFactory
                                .newLatLngZoom(defaultLocation, DEFAULT_ZOOM));
                        map.getUiSettings().setMyLocationButtonEnabled(false);
                    }
                }
            });
        }
    } catch (SecurityException e)  {
        Log.e("Exception: %s", e.getMessage(), e);
    }
}
MapsActivityCurrentPlace.java

Kotlin

@SuppressLint("MissingPermission")
private fun getDeviceLocation() {
    /*
     * Get the best and most recent location of the device, which may be null in rare
     * cases when a location is not available.
     */
    try {
        if (locationPermissionGranted) {
            val locationResult = fusedLocationProviderClient.lastLocation
            locationResult.addOnCompleteListener(this) { task ->
                if (task.isSuccessful) {
                    // Set the map's camera position to the current location of the device.
                    lastKnownLocation = task.result
                    if (lastKnownLocation != null) {
                        map?.moveCamera(CameraUpdateFactory.newLatLngZoom(
                            LatLng(lastKnownLocation!!.latitude,
                                lastKnownLocation!!.longitude), DEFAULT_ZOOM.toFloat()))
                    }
                } else {
                    Log.d(TAG, "Current location is null. Using defaults.")
                    Log.e(TAG, "Exception: %s", task.exception)
                    map?.moveCamera(CameraUpdateFactory
                        .newLatLngZoom(defaultLocation, DEFAULT_ZOOM.toFloat()))
                    map?.uiSettings?.isMyLocationButtonEnabled = false
                }
            }
        }
    } catch (e: SecurityException) {
        Log.e("Exception: %s", e.message, e)
    }
}
MapsActivityCurrentPlace.kt

Ottieni il luogo attuale

Utilizza l'SDK Places per Android per ottenere un elenco dei luoghi più probabili nella posizione attuale del dispositivo. In questo contesto, un luogo rappresenta un'attività o un altro punto d'interesse.

Questo tutorial ottiene la posizione attuale quando l'utente fa clic su un pulsante Ottieni luogo. Offre all'utente un elenco di luoghi probabili tra cui scegliere, poi aggiunge un indicatore sulla mappa in corrispondenza del luogo selezionato. Il tutorial fornisce il codice necessario per interagire con l'SDK Places per Android. Per maggiori dettagli, consulta la guida su come recuperare il luogo attuale.

1. Crea un file di layout (current_place_menu.xml) per il menu opzioni e sostituisci il metodo onCreateOptionsMenu() per configurare il menu opzioni. Per il codice, vedi l'app di esempio fornita.
2. Sostituisci il metodo onOptionsItemSelected() per ottenere il luogo corrente quando l'utente fa clic sull'opzione Ottieni luogo:

   Java

   @Override
   public boolean onOptionsItemSelected(MenuItem item) {
       if (item.getItemId() == R.id.option_get_place) {
           showCurrentPlace();
       }
       return true;
   }
   MapsActivityCurrentPlace.java
   

   Kotlin

   override fun onOptionsItemSelected(item: MenuItem): Boolean {
       if (item.itemId == R.id.option_get_place) {
           showCurrentPlace()
       }
       return true
   }
   MapsActivityCurrentPlace.kt
   

3. Crea un metodo showCurrentPlace() per ottenere un elenco di luoghi probabili nella posizione attuale del dispositivo:

   Java

   private void showCurrentPlace() {
       if (map == null) {
           return;
       }
   
       if (locationPermissionGranted) {
           // Use fields to define the data types to return.
           List<Place.Field> placeFields = Arrays.asList(Place.Field.NAME, Place.Field.ADDRESS,
                   Place.Field.LAT_LNG);
   
           // Use the builder to create a FindCurrentPlaceRequest.
           FindCurrentPlaceRequest request =
                   FindCurrentPlaceRequest.newInstance(placeFields);
   
           // Get the likely places - that is, the businesses and other points of interest that
           // are the best match for the device's current location.
           @SuppressWarnings("MissingPermission") final
           Task<FindCurrentPlaceResponse> placeResult =
                   placesClient.findCurrentPlace(request);
           placeResult.addOnCompleteListener (new OnCompleteListener<FindCurrentPlaceResponse>() {
               @Override
               public void onComplete(@NonNull Task<FindCurrentPlaceResponse> task) {
                   if (task.isSuccessful() && task.getResult() != null) {
                       FindCurrentPlaceResponse likelyPlaces = task.getResult();
   
                       // Set the count, handling cases where less than 5 entries are returned.
                       int count;
                       if (likelyPlaces.getPlaceLikelihoods().size() < M_MAX_ENTRIES) {
                           count = likelyPlaces.getPlaceLikelihoods().size();
                       } else {
                           count = M_MAX_ENTRIES;
                       }
   
                       int i = 0;
                       likelyPlaceNames = new String[count];
                       likelyPlaceAddresses = new String[count];
                       likelyPlaceAttributions = new List[count];
                       likelyPlaceLatLngs = new LatLng[count];
   
                       for (PlaceLikelihood placeLikelihood : likelyPlaces.getPlaceLikelihoods()) {
                           // Build a list of likely places to show the user.
                           likelyPlaceNames[i] = placeLikelihood.getPlace().getName();
                           likelyPlaceAddresses[i] = placeLikelihood.getPlace().getAddress();
                           likelyPlaceAttributions[i] = placeLikelihood.getPlace()
                                   .getAttributions();
                           likelyPlaceLatLngs[i] = placeLikelihood.getPlace().getLatLng();
   
                           i++;
                           if (i > (count - 1)) {
                               break;
                           }
                       }
   
                       // Show a dialog offering the user the list of likely places, and add a
                       // marker at the selected place.
                       MapsActivityCurrentPlace.this.openPlacesDialog();
                   }
                   else {
                       Log.e(TAG, "Exception: %s", task.getException());
                   }
               }
           });
       } else {
           // The user has not granted permission.
           Log.i(TAG, "The user did not grant location permission.");
   
           // Add a default marker, because the user hasn't selected a place.
           map.addMarker(new MarkerOptions()
                   .title(getString(R.string.default_info_title))
                   .position(defaultLocation)
                   .snippet(getString(R.string.default_info_snippet)));
   
           // Prompt the user for permission.
           getLocationPermission();
       }
   }
   MapsActivityCurrentPlace.java
   

   Kotlin

   @SuppressLint("MissingPermission")
   private fun showCurrentPlace() {
       if (map == null) {
           return
       }
       if (locationPermissionGranted) {
           // Use fields to define the data types to return.
           val placeFields = listOf(Place.Field.NAME, Place.Field.ADDRESS, Place.Field.LAT_LNG)
   
           // Use the builder to create a FindCurrentPlaceRequest.
           val request = FindCurrentPlaceRequest.newInstance(placeFields)
   
           // Get the likely places - that is, the businesses and other points of interest that
           // are the best match for the device's current location.
           val placeResult = placesClient.findCurrentPlace(request)
           placeResult.addOnCompleteListener { task ->
               if (task.isSuccessful && task.result != null) {
                   val likelyPlaces = task.result
   
                   // Set the count, handling cases where less than 5 entries are returned.
                   val count = if (likelyPlaces != null && likelyPlaces.placeLikelihoods.size < M_MAX_ENTRIES) {
                       likelyPlaces.placeLikelihoods.size
                   } else {
                       M_MAX_ENTRIES
                   }
                   var i = 0
                   likelyPlaceNames = arrayOfNulls(count)
                   likelyPlaceAddresses = arrayOfNulls(count)
                   likelyPlaceAttributions = arrayOfNulls<List<*>?>(count)
                   likelyPlaceLatLngs = arrayOfNulls(count)
                   for (placeLikelihood in likelyPlaces?.placeLikelihoods ?: emptyList()) {
                       // Build a list of likely places to show the user.
                       likelyPlaceNames[i] = placeLikelihood.place.name
                       likelyPlaceAddresses[i] = placeLikelihood.place.address
                       likelyPlaceAttributions[i] = placeLikelihood.place.attributions
                       likelyPlaceLatLngs[i] = placeLikelihood.place.latLng
                       i++
                       if (i > count - 1) {
                           break
                       }
                   }
   
                   // Show a dialog offering the user the list of likely places, and add a
                   // marker at the selected place.
                   openPlacesDialog()
               } else {
                   Log.e(TAG, "Exception: %s", task.exception)
               }
           }
       } else {
           // The user has not granted permission.
           Log.i(TAG, "The user did not grant location permission.")
   
           // Add a default marker, because the user hasn't selected a place.
           map?.addMarker(MarkerOptions()
               .title(getString(R.string.default_info_title))
               .position(defaultLocation)
               .snippet(getString(R.string.default_info_snippet)))
   
           // Prompt the user for permission.
           getLocationPermission()
       }
   }
   MapsActivityCurrentPlace.kt
   

4. Crea un metodo openPlacesDialog() per visualizzare un modulo che consenta all'utente di selezionare un luogo da un elenco di luoghi probabili. Aggiungi un indicatore sulla mappa per il luogo selezionato. Il contenuto dell'indicatore include il nome e l'indirizzo del luogo ed eventuali attribuzioni fornite dall'API:

   Java

   private void openPlacesDialog() {
       // Ask the user to choose the place where they are now.
       DialogInterface.OnClickListener listener = new DialogInterface.OnClickListener() {
           @Override
           public void onClick(DialogInterface dialog, int which) {
               // The "which" argument contains the position of the selected item.
               LatLng markerLatLng = likelyPlaceLatLngs[which];
               String markerSnippet = likelyPlaceAddresses[which];
               if (likelyPlaceAttributions[which] != null) {
                   markerSnippet = markerSnippet + "\n" + likelyPlaceAttributions[which];
               }
   
               // Add a marker for the selected place, with an info window
               // showing information about that place.
               map.addMarker(new MarkerOptions()
                       .title(likelyPlaceNames[which])
                       .position(markerLatLng)
                       .snippet(markerSnippet));
   
               // Position the map's camera at the location of the marker.
               map.moveCamera(CameraUpdateFactory.newLatLngZoom(markerLatLng,
                       DEFAULT_ZOOM));
           }
       };
   
       // Display the dialog.
       AlertDialog dialog = new AlertDialog.Builder(this)
               .setTitle(R.string.pick_place)
               .setItems(likelyPlaceNames, listener)
               .show();
   }
   MapsActivityCurrentPlace.java
   

   Kotlin

   private fun openPlacesDialog() {
       // Ask the user to choose the place where they are now.
       val listener = DialogInterface.OnClickListener { dialog, which -> // The "which" argument contains the position of the selected item.
           val markerLatLng = likelyPlaceLatLngs[which]
           var markerSnippet = likelyPlaceAddresses[which]
           if (likelyPlaceAttributions[which] != null) {
               markerSnippet = """
                   $markerSnippet
                   ${likelyPlaceAttributions[which]}
                   """.trimIndent()
           }
   
           if (markerLatLng == null) {
               return@OnClickListener
           }
   
           // Add a marker for the selected place, with an info window
           // showing information about that place.
           map?.addMarker(MarkerOptions()
               .title(likelyPlaceNames[which])
               .position(markerLatLng)
               .snippet(markerSnippet))
   
           // Position the map's camera at the location of the marker.
           map?.moveCamera(CameraUpdateFactory.newLatLngZoom(markerLatLng,
               DEFAULT_ZOOM.toFloat()))
       }
   
       // Display the dialog.
       AlertDialog.Builder(this)
           .setTitle(R.string.pick_place)
           .setItems(likelyPlaceNames, listener)
           .show()
   }
   MapsActivityCurrentPlace.kt
   

5. Crea un layout personalizzato per i contenuti della finestra informativa. In questo modo è possibile visualizzare più righe di contenuti nella finestra informativa. Innanzitutto, aggiungi un file di layout XML, custom_info_contents.xml, contenente una visualizzazione di testo per il titolo della finestra informativa e un'altra visualizzazione di testo per lo snippet (ovvero i contenuti testuali della finestra informativa):

   <?xml version="1.0" encoding="utf-8"?>
   <!--
    Copyright 2020 Google LLC
   
    Licensed under the Apache License, Version 2.0 (the "License");
    you may not use this file except in compliance with the License.
    You may obtain a copy of the License at
   
         http://www.apache.org/licenses/LICENSE-2.0
   
    Unless required by applicable law or agreed to in writing, software
    distributed under the License is distributed on an "AS IS" BASIS,
    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    See the License for the specific language governing permissions and
    limitations under the License.
   -->
   
   <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
       android:layout_width="wrap_content"
       android:layout_height="wrap_content"
       android:layoutDirection="locale"
       android:orientation="vertical">
       <TextView
           android:id="@+id/title"
           android:layout_width="wrap_content"
           android:layout_height="wrap_content"
           android:layout_gravity="center_horizontal"
           android:textColor="#ff000000"
           android:textStyle="bold" />
   
       <TextView
           android:id="@+id/snippet"
           android:layout_width="wrap_content"
           android:layout_height="wrap_content"
           android:textColor="#ff7f7f7f" />
   </LinearLayout>
   
   

6. Implementa l'interfaccia di InfoWindowAdapter per gonfiare il layout e caricare i contenuti della finestra informativa:

   Java

   // Use a custom info window adapter to handle multiple lines of text in the
   // info window contents.
   this.map.setInfoWindowAdapter(new GoogleMap.InfoWindowAdapter() {
   
       @Override
       // Return null here, so that getInfoContents() is called next.
       public View getInfoWindow(Marker arg0) {
           return null;
       }
   
       @Override
       public View getInfoContents(Marker marker) {
           // Inflate the layouts for the info window, title and snippet.
           View infoWindow = getLayoutInflater().inflate(R.layout.custom_info_contents,
                   (FrameLayout) findViewById(R.id.map), false);
   
           TextView title = infoWindow.findViewById(R.id.title);
           title.setText(marker.getTitle());
   
           TextView snippet = infoWindow.findViewById(R.id.snippet);
           snippet.setText(marker.getSnippet());
   
           return infoWindow;
       }
   });
   MapsActivityCurrentPlace.java
   

   Kotlin

   // Use a custom info window adapter to handle multiple lines of text in the
   // info window contents.
   this.map?.setInfoWindowAdapter(object : InfoWindowAdapter {
       // Return null here, so that getInfoContents() is called next.
       override fun getInfoWindow(arg0: Marker): View? {
           return null
       }
   
       override fun getInfoContents(marker: Marker): View {
           // Inflate the layouts for the info window, title and snippet.
           val infoWindow = layoutInflater.inflate(R.layout.custom_info_contents,
               findViewById<FrameLayout>(R.id.map), false)
           val title = infoWindow.findViewById<TextView>(R.id.title)
           title.text = marker.title
           val snippet = infoWindow.findViewById<TextView>(R.id.snippet)
           snippet.text = marker.snippet
           return infoWindow
       }
   })
   MapsActivityCurrentPlace.kt
   

Nota: per impostazione predefinita, Maps SDK for Android mostra i contenuti della finestra informativa quando l'utente tocca un indicatore. Non è necessario aggiungere un listener di clic per l'indicatore se vuoi utilizzare il comportamento predefinito.

Salvare lo stato della mappa

Salva la posizione della fotocamera della mappa e della posizione del dispositivo. Quando un utente ruota un dispositivo Android o apporta modifiche alla configurazione, il framework Android elimina e ricrea l'attività della mappa. Per garantire un'esperienza utente ottimale, è consigliabile archiviare lo stato pertinente dell'applicazione e ripristinarlo quando necessario.

Questo tutorial fornisce tutto il codice necessario per salvare lo stato della mappa. Per maggiori dettagli, consulta la guida al bundle savedInstanceState.

1. Nella tua attività sulla mappa, configura le coppie chiave-valore per memorizzare lo stato dell'attività:

   Java

   private static final String KEY_CAMERA_POSITION = "camera_position";
   private static final String KEY_LOCATION = "location";
   MapsActivityCurrentPlace.java
   

   Kotlin

   private const val KEY_CAMERA_POSITION = "camera_position"
   private const val KEY_LOCATION = "location"
   MapsActivityCurrentPlace.kt
   

2. Implementa il callback onSaveInstanceState() per salvare lo stato quando l'attività viene messa in pausa:

   Java

   @Override
   protected void onSaveInstanceState(Bundle outState) {
       if (map != null) {
           outState.putParcelable(KEY_CAMERA_POSITION, map.getCameraPosition());
           outState.putParcelable(KEY_LOCATION, lastKnownLocation);
       }
       super.onSaveInstanceState(outState);
   }
   MapsActivityCurrentPlace.java
   

   Kotlin

   override fun onSaveInstanceState(outState: Bundle) {
       map?.let { map ->
           outState.putParcelable(KEY_CAMERA_POSITION, map.cameraPosition)
           outState.putParcelable(KEY_LOCATION, lastKnownLocation)
       }
       super.onSaveInstanceState(outState)
   }
   MapsActivityCurrentPlace.kt
   

3. Nel metodo onCreate() della tua attività, recupera la posizione del dispositivo e la posizione della fotocamera della mappa se salvata in precedenza:

   Java

   // Retrieve location and camera position from saved instance state.
   if (savedInstanceState != null) {
       lastKnownLocation = savedInstanceState.getParcelable(KEY_LOCATION);
       cameraPosition = savedInstanceState.getParcelable(KEY_CAMERA_POSITION);
   }
   MapsActivityCurrentPlace.java
   

   Kotlin

   if (savedInstanceState != null) {
       lastKnownLocation = savedInstanceState.getParcelable(KEY_LOCATION)
       cameraPosition = savedInstanceState.getParcelable(KEY_CAMERA_POSITION)
   }
   MapsActivityCurrentPlace.kt
   

Congratulazioni! Hai creato un'app per Android che mostra il luogo attuale su una mappa di Google. Hai anche imparato a utilizzare l'SDK Maps per Android, l'SDK Places per Android e il fornitore di servizi di localizzazione.