自定义叠加层

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简介

叠加层是地图上与纬度/经度坐标绑定的对象,会随着您拖动或缩放地图而移动。如需了解预定义的叠加层类型,请参阅在地图上绘图

Maps JavaScript API 提供了一个 OverlayView 类,用于创建您自己的自定义叠加层。OverlayView 是一个基类,提供了您在创建叠加层时必须实现的几种方法。该类还提供了几种方法,可让您在屏幕坐标和地图上的位置之间进行转换。

添加自定义叠层

下面概要列出了创建自定义叠层所需的步骤:

  • 将自定义叠加层对象的 prototype 设置为 google.maps.OverlayView() 的新实例。实际上,这将是叠加层类的子类。
  • 为自定义叠加层创建构造函数,并设置所有初始化参数。
  • 在原型中实现 onAdd() 方法,并将叠加层附加到地图。在地图准备好附加叠加层后,系统会调用 OverlayView.onAdd()
  • 在原型中实现 draw() 方法,并处理对象的视觉显示。首次显示对象时,系统会调用 OverlayView.draw()
  • 您还应实现 onRemove() 方法,以清理您在叠加层中添加的所有元素。

以下是各个步骤的详情。您可以查看完整有效的示例代码:查看示例代码

子类化叠层

以下示例使用 OverlayView 创建简单的图片叠加层。

现在,我们为 USGSOverlay 类创建一个构造函数,并将传递的参数初始化为新对象的属性。

TypeScript

/**
 * The custom USGSOverlay object contains the USGS image,
 * the bounds of the image, and a reference to the map.
 */
class USGSOverlay extends google.maps.OverlayView {
  private bounds: google.maps.LatLngBounds;
  private image: string;
  private div?: HTMLElement;

  constructor(bounds: google.maps.LatLngBounds, image: string) {
    super();

    this.bounds = bounds;
    this.image = image;
  }

JavaScript

/**
 * The custom USGSOverlay object contains the USGS image,
 * the bounds of the image, and a reference to the map.
 */
class USGSOverlay extends google.maps.OverlayView {
  bounds;
  image;
  div;
  constructor(bounds, image) {
    super();
    this.bounds = bounds;
    this.image = image;
  }

目前,我们还无法在叠加层的构造函数中将此叠加层附加到地图。首先,我们需要确保所有地图窗格都可用,因为它们用于指定对象在地图上的显示顺序。该 API 提供了一个辅助方法,用于指明已发生这种情况。我们将在下一部分中介绍如何处理该方法。

初始化叠层

叠加层首次被实例化并准备好显示后,我们需要通过浏览器的 DOM 将叠加层附加到地图。该 API 会通过调用叠加层的 onAdd() 方法来指示该叠加层已添加到地图中。为了处理此方法,我们创建一个 <div> 来保存图片,添加 <img> 元素,将其附加到 <div>,然后将叠加层附加到地图的某个窗格。窗格是 DOM 树中的一个节点。

类型为 MapPanes 的窗格用于指定地图上不同图层的堆叠顺序。您可以使用以下窗格,并按以下枚举顺序(从下到上)堆叠这些窗格:

  • mapPane 是最低的窗格,位于图块上方。可能无法接收 DOM 事件。(窗格 0)
  • overlayLayer 包含多段线、多边形、地面叠加层和图块图层叠加层。该窗格可能无法接收DOM事件(窗格 1)
  • markerLayer 包含标记。该窗格可能无法接收DOM事件(窗格 2)
  • overlayMouseTarget 包含接收 DOM 事件的元素。(窗格 3)
  • floatPane 包含信息窗口。该窗格位于所有地图叠加层之上(窗格 4)

由于我们的图片为“地面叠加层”,因此我们将使用 overlayLayer 窗格。创建该窗格后,我们会将对象作为子对象附加到窗格。

TypeScript

/**
 * onAdd is called when the map's panes are ready and the overlay has been
 * added to the map.
 */
onAdd() {
  this.div = document.createElement("div");
  this.div.style.borderStyle = "none";
  this.div.style.borderWidth = "0px";
  this.div.style.position = "absolute";

  // Create the img element and attach it to the div.
  const img = document.createElement("img");

  img.src = this.image;
  img.style.width = "100%";
  img.style.height = "100%";
  img.style.position = "absolute";
  this.div.appendChild(img);

  // Add the element to the "overlayLayer" pane.
  const panes = this.getPanes()!;

  panes.overlayLayer.appendChild(this.div);
}

JavaScript

/**
 * onAdd is called when the map's panes are ready and the overlay has been
 * added to the map.
 */
onAdd() {
  this.div = document.createElement("div");
  this.div.style.borderStyle = "none";
  this.div.style.borderWidth = "0px";
  this.div.style.position = "absolute";

  // Create the img element and attach it to the div.
  const img = document.createElement("img");

  img.src = this.image;
  img.style.width = "100%";
  img.style.height = "100%";
  img.style.position = "absolute";
  this.div.appendChild(img);

  // Add the element to the "overlayLayer" pane.
  const panes = this.getPanes();

  panes.overlayLayer.appendChild(this.div);
}

绘制叠层

请注意,在上述代码中,我们并未调用任何特殊的视觉显示。每当需要在地图上绘制叠加层(包括首次添加叠加层)时,API 都会对叠加层调用单独的 draw() 方法。

因此,我们将实现此 draw() 方法,使用 getProjection() 检索叠加层的 MapCanvasProjection,并计算对象的右上角和左下角锚定点的精确坐标。然后,我们可以调整 <div> 的大小。进而调整图片的大小,使之与我们在叠加层的构造函数中指定的范围一致。

TypeScript

draw() {
  // We use the south-west and north-east
  // coordinates of the overlay to peg it to the correct position and size.
  // To do this, we need to retrieve the projection from the overlay.
  const overlayProjection = this.getProjection();

  // Retrieve the south-west and north-east coordinates of this overlay
  // in LatLngs and convert them to pixel coordinates.
  // We'll use these coordinates to resize the div.
  const sw = overlayProjection.fromLatLngToDivPixel(
    this.bounds.getSouthWest()
  )!;
  const ne = overlayProjection.fromLatLngToDivPixel(
    this.bounds.getNorthEast()
  )!;

  // Resize the image's div to fit the indicated dimensions.
  if (this.div) {
    this.div.style.left = sw.x + "px";
    this.div.style.top = ne.y + "px";
    this.div.style.width = ne.x - sw.x + "px";
    this.div.style.height = sw.y - ne.y + "px";
  }
}

JavaScript

draw() {
  // We use the south-west and north-east
  // coordinates of the overlay to peg it to the correct position and size.
  // To do this, we need to retrieve the projection from the overlay.
  const overlayProjection = this.getProjection();
  // Retrieve the south-west and north-east coordinates of this overlay
  // in LatLngs and convert them to pixel coordinates.
  // We'll use these coordinates to resize the div.
  const sw = overlayProjection.fromLatLngToDivPixel(
    this.bounds.getSouthWest()
  );
  const ne = overlayProjection.fromLatLngToDivPixel(
    this.bounds.getNorthEast()
  );

  // Resize the image's div to fit the indicated dimensions.
  if (this.div) {
    this.div.style.left = sw.x + "px";
    this.div.style.top = ne.y + "px";
    this.div.style.width = ne.x - sw.x + "px";
    this.div.style.height = sw.y - ne.y + "px";
  }
}

移除自定义叠层

我们还添加了 onRemove() 方法,用于从地图彻底移除叠加层。

TypeScript

/**
 * The onRemove() method will be called automatically from the API if
 * we ever set the overlay's map property to 'null'.
 */
onRemove() {
  if (this.div) {
    (this.div.parentNode as HTMLElement).removeChild(this.div);
    delete this.div;
  }
}

JavaScript

/**
 * The onRemove() method will be called automatically from the API if
 * we ever set the overlay's map property to 'null'.
 */
onRemove() {
  if (this.div) {
    this.div.parentNode.removeChild(this.div);
    delete this.div;
  }
}

隐藏和显示自定义叠层

如果您想隐藏或显示(而不只是创建或移除)叠加层,您可以实现自己的 hide()show() 方法,以调整叠加层的可见性。或者,您也可以将叠加层与地图的 DOM 分离,不过此操作的成本略高。请注意,如果您随后将叠加层重新附加到地图的 DOM,系统将会重新调用叠加层的 onAdd() 方法。

以下示例展示了如何向叠加层的原型添加 hide()show() 方法,用于切换容器 <div> 的可见性。此外,我们还添加了 toggleDOM() 方法,该方法可将叠加层附加到地图,或将两者分离开来。

TypeScript

/**
 *  Set the visibility to 'hidden' or 'visible'.
 */
hide() {
  if (this.div) {
    this.div.style.visibility = "hidden";
  }
}

show() {
  if (this.div) {
    this.div.style.visibility = "visible";
  }
}

toggle() {
  if (this.div) {
    if (this.div.style.visibility === "hidden") {
      this.show();
    } else {
      this.hide();
    }
  }
}

toggleDOM(map: google.maps.Map) {
  if (this.getMap()) {
    this.setMap(null);
  } else {
    this.setMap(map);
  }
}

JavaScript

/**
 *  Set the visibility to 'hidden' or 'visible'.
 */
hide() {
  if (this.div) {
    this.div.style.visibility = "hidden";
  }
}
show() {
  if (this.div) {
    this.div.style.visibility = "visible";
  }
}
toggle() {
  if (this.div) {
    if (this.div.style.visibility === "hidden") {
      this.show();
    } else {
      this.hide();
    }
  }
}
toggleDOM(map) {
  if (this.getMap()) {
    this.setMap(null);
  } else {
    this.setMap(map);
  }
}

添加按钮控件

为了触发 toggletoggleDom 方法,系统会向地图中添加按钮控件。

TypeScript

const toggleButton = document.createElement("button");

toggleButton.textContent = "Toggle";
toggleButton.classList.add("custom-map-control-button");

const toggleDOMButton = document.createElement("button");

toggleDOMButton.textContent = "Toggle DOM Attachment";
toggleDOMButton.classList.add("custom-map-control-button");

toggleButton.addEventListener("click", () => {
  overlay.toggle();
});

toggleDOMButton.addEventListener("click", () => {
  overlay.toggleDOM(map);
});

map.controls[google.maps.ControlPosition.TOP_RIGHT].push(toggleDOMButton);
map.controls[google.maps.ControlPosition.TOP_RIGHT].push(toggleButton);

JavaScript

const toggleButton = document.createElement("button");

toggleButton.textContent = "Toggle";
toggleButton.classList.add("custom-map-control-button");

const toggleDOMButton = document.createElement("button");

toggleDOMButton.textContent = "Toggle DOM Attachment";
toggleDOMButton.classList.add("custom-map-control-button");
toggleButton.addEventListener("click", () => {
  overlay.toggle();
});
toggleDOMButton.addEventListener("click", () => {
  overlay.toggleDOM(map);
});
map.controls[google.maps.ControlPosition.TOP_RIGHT].push(toggleDOMButton);
map.controls[google.maps.ControlPosition.TOP_RIGHT].push(toggleButton);

完整的示例代码

完整的示例代码如下所示:

TypeScript

// This example adds hide() and show() methods to a custom overlay's prototype.
// These methods toggle the visibility of the container <div>.
// overlay to or from the map.

function initMap(): void {
  const map = new google.maps.Map(
    document.getElementById("map") as HTMLElement,
    {
      zoom: 11,
      center: { lat: 62.323907, lng: -150.109291 },
      mapTypeId: "satellite",
    }
  );

  const bounds = new google.maps.LatLngBounds(
    new google.maps.LatLng(62.281819, -150.287132),
    new google.maps.LatLng(62.400471, -150.005608)
  );

  // The photograph is courtesy of the U.S. Geological Survey.
  let image = "https://developers.google.com/maps/documentation/javascript/";

  image += "examples/full/images/talkeetna.png";

  /**
   * The custom USGSOverlay object contains the USGS image,
   * the bounds of the image, and a reference to the map.
   */
  class USGSOverlay extends google.maps.OverlayView {
    private bounds: google.maps.LatLngBounds;
    private image: string;
    private div?: HTMLElement;

    constructor(bounds: google.maps.LatLngBounds, image: string) {
      super();

      this.bounds = bounds;
      this.image = image;
    }

    /**
     * onAdd is called when the map's panes are ready and the overlay has been
     * added to the map.
     */
    onAdd() {
      this.div = document.createElement("div");
      this.div.style.borderStyle = "none";
      this.div.style.borderWidth = "0px";
      this.div.style.position = "absolute";

      // Create the img element and attach it to the div.
      const img = document.createElement("img");

      img.src = this.image;
      img.style.width = "100%";
      img.style.height = "100%";
      img.style.position = "absolute";
      this.div.appendChild(img);

      // Add the element to the "overlayLayer" pane.
      const panes = this.getPanes()!;

      panes.overlayLayer.appendChild(this.div);
    }

    draw() {
      // We use the south-west and north-east
      // coordinates of the overlay to peg it to the correct position and size.
      // To do this, we need to retrieve the projection from the overlay.
      const overlayProjection = this.getProjection();

      // Retrieve the south-west and north-east coordinates of this overlay
      // in LatLngs and convert them to pixel coordinates.
      // We'll use these coordinates to resize the div.
      const sw = overlayProjection.fromLatLngToDivPixel(
        this.bounds.getSouthWest()
      )!;
      const ne = overlayProjection.fromLatLngToDivPixel(
        this.bounds.getNorthEast()
      )!;

      // Resize the image's div to fit the indicated dimensions.
      if (this.div) {
        this.div.style.left = sw.x + "px";
        this.div.style.top = ne.y + "px";
        this.div.style.width = ne.x - sw.x + "px";
        this.div.style.height = sw.y - ne.y + "px";
      }
    }

    /**
     * The onRemove() method will be called automatically from the API if
     * we ever set the overlay's map property to 'null'.
     */
    onRemove() {
      if (this.div) {
        (this.div.parentNode as HTMLElement).removeChild(this.div);
        delete this.div;
      }
    }

    /**
     *  Set the visibility to 'hidden' or 'visible'.
     */
    hide() {
      if (this.div) {
        this.div.style.visibility = "hidden";
      }
    }

    show() {
      if (this.div) {
        this.div.style.visibility = "visible";
      }
    }

    toggle() {
      if (this.div) {
        if (this.div.style.visibility === "hidden") {
          this.show();
        } else {
          this.hide();
        }
      }
    }

    toggleDOM(map: google.maps.Map) {
      if (this.getMap()) {
        this.setMap(null);
      } else {
        this.setMap(map);
      }
    }
  }

  const overlay: USGSOverlay = new USGSOverlay(bounds, image);

  overlay.setMap(map);

  const toggleButton = document.createElement("button");

  toggleButton.textContent = "Toggle";
  toggleButton.classList.add("custom-map-control-button");

  const toggleDOMButton = document.createElement("button");

  toggleDOMButton.textContent = "Toggle DOM Attachment";
  toggleDOMButton.classList.add("custom-map-control-button");

  toggleButton.addEventListener("click", () => {
    overlay.toggle();
  });

  toggleDOMButton.addEventListener("click", () => {
    overlay.toggleDOM(map);
  });

  map.controls[google.maps.ControlPosition.TOP_RIGHT].push(toggleDOMButton);
  map.controls[google.maps.ControlPosition.TOP_RIGHT].push(toggleButton);
}

declare global {
  interface Window {
    initMap: () => void;
  }
}
window.initMap = initMap;

JavaScript

// This example adds hide() and show() methods to a custom overlay's prototype.
// These methods toggle the visibility of the container <div>.
// overlay to or from the map.
function initMap() {
  const map = new google.maps.Map(document.getElementById("map"), {
    zoom: 11,
    center: { lat: 62.323907, lng: -150.109291 },
    mapTypeId: "satellite",
  });
  const bounds = new google.maps.LatLngBounds(
    new google.maps.LatLng(62.281819, -150.287132),
    new google.maps.LatLng(62.400471, -150.005608)
  );
  // The photograph is courtesy of the U.S. Geological Survey.
  let image = "https://developers.google.com/maps/documentation/javascript/";

  image += "examples/full/images/talkeetna.png";
  /**
   * The custom USGSOverlay object contains the USGS image,
   * the bounds of the image, and a reference to the map.
   */
  class USGSOverlay extends google.maps.OverlayView {
    bounds;
    image;
    div;
    constructor(bounds, image) {
      super();
      this.bounds = bounds;
      this.image = image;
    }
    /**
     * onAdd is called when the map's panes are ready and the overlay has been
     * added to the map.
     */
    onAdd() {
      this.div = document.createElement("div");
      this.div.style.borderStyle = "none";
      this.div.style.borderWidth = "0px";
      this.div.style.position = "absolute";

      // Create the img element and attach it to the div.
      const img = document.createElement("img");

      img.src = this.image;
      img.style.width = "100%";
      img.style.height = "100%";
      img.style.position = "absolute";
      this.div.appendChild(img);

      // Add the element to the "overlayLayer" pane.
      const panes = this.getPanes();

      panes.overlayLayer.appendChild(this.div);
    }
    draw() {
      // We use the south-west and north-east
      // coordinates of the overlay to peg it to the correct position and size.
      // To do this, we need to retrieve the projection from the overlay.
      const overlayProjection = this.getProjection();
      // Retrieve the south-west and north-east coordinates of this overlay
      // in LatLngs and convert them to pixel coordinates.
      // We'll use these coordinates to resize the div.
      const sw = overlayProjection.fromLatLngToDivPixel(
        this.bounds.getSouthWest()
      );
      const ne = overlayProjection.fromLatLngToDivPixel(
        this.bounds.getNorthEast()
      );

      // Resize the image's div to fit the indicated dimensions.
      if (this.div) {
        this.div.style.left = sw.x + "px";
        this.div.style.top = ne.y + "px";
        this.div.style.width = ne.x - sw.x + "px";
        this.div.style.height = sw.y - ne.y + "px";
      }
    }
    /**
     * The onRemove() method will be called automatically from the API if
     * we ever set the overlay's map property to 'null'.
     */
    onRemove() {
      if (this.div) {
        this.div.parentNode.removeChild(this.div);
        delete this.div;
      }
    }
    /**
     *  Set the visibility to 'hidden' or 'visible'.
     */
    hide() {
      if (this.div) {
        this.div.style.visibility = "hidden";
      }
    }
    show() {
      if (this.div) {
        this.div.style.visibility = "visible";
      }
    }
    toggle() {
      if (this.div) {
        if (this.div.style.visibility === "hidden") {
          this.show();
        } else {
          this.hide();
        }
      }
    }
    toggleDOM(map) {
      if (this.getMap()) {
        this.setMap(null);
      } else {
        this.setMap(map);
      }
    }
  }

  const overlay = new USGSOverlay(bounds, image);

  overlay.setMap(map);

  const toggleButton = document.createElement("button");

  toggleButton.textContent = "Toggle";
  toggleButton.classList.add("custom-map-control-button");

  const toggleDOMButton = document.createElement("button");

  toggleDOMButton.textContent = "Toggle DOM Attachment";
  toggleDOMButton.classList.add("custom-map-control-button");
  toggleButton.addEventListener("click", () => {
    overlay.toggle();
  });
  toggleDOMButton.addEventListener("click", () => {
    overlay.toggleDOM(map);
  });
  map.controls[google.maps.ControlPosition.TOP_RIGHT].push(toggleDOMButton);
  map.controls[google.maps.ControlPosition.TOP_RIGHT].push(toggleButton);
}

window.initMap = initMap;

CSS

/* 
 * Always set the map height explicitly to define the size of the div element
 * that contains the map. 
 */
#map {
  height: 100%;
}

/* 
 * Optional: Makes the sample page fill the window. 
 */
html,
body {
  height: 100%;
  margin: 0;
  padding: 0;
}

.custom-map-control-button {
  background-color: #fff;
  border: 0;
  border-radius: 2px;
  box-shadow: 0 1px 4px -1px rgba(0, 0, 0, 0.3);
  margin: 10px;
  padding: 0 0.5em;
  font: 400 18px Roboto, Arial, sans-serif;
  overflow: hidden;
  height: 40px;
  cursor: pointer;
}
.custom-map-control-button:hover {
  background: rgb(235, 235, 235);
}

HTML

<html>
  <head>
    <title>Showing/Hiding Overlays</title>
    <script src="https://polyfill.io/v3/polyfill.min.js?features=default"></script>

    <link rel="stylesheet" type="text/css" href="./style.css" />
    <script type="module" src="./index.js"></script>
  </head>
  <body>
    <div id="map"></div>

    <!-- 
     The `defer` attribute causes the callback to execute after the full HTML
     document has been parsed. For non-blocking uses, avoiding race conditions,
     and consistent behavior across browsers, consider loading using Promises
     with https://www.npmjs.com/package/@googlemaps/js-api-loader.
    -->
    <script
      src="https://maps.googleapis.com/maps/api/js?key=AIzaSyB41DRUbKWJHPxaFjMAwdrzWzbVKartNGg&callback=initMap&v=weekly"
      defer
    ></script>
  </body>
</html>

试用示例