iOS Permissions and Discovery

Page Summary

Updating your iOS Cast sender app to Google Cast SDK v4.6.0 or later is necessary to maintain Cast functionality with iOS 14 due to new restrictions and permissions.
Beginning with iOS 14, applications scanning for local network devices will prompt users for one-time permission, and denying this will prevent casting.
To update your app for iOS 14, you need to add Cast iOS SDK 4.8.4, specify NSBonjourServices and NSLocalNetworkUsageDescription in your Info.plist, and re-release your app.
If using a custom device picker with Cast SDK 4.6.0 or later, you must explicitly call the startDiscovery method to initiate device discovery.

Applications that scan for devices on the local network will now prompt users with a one-time permissions dialog to find and connect to local network devices. The Cast platform uses the local network to discover and control Cast devices, so if the user denies permission, they will not be able to cast.

To improve the user experience, we are making some UX modifications to the SDK for those apps that are using the standard device picker. These UX modifications make it more obvious to users why local network access permissions are needed, as well as how to enable casting if local network device access has been disabled.

The Cast iOS SDK v4.6.0 or later can be added with Swift Package Manager by following the Swift Package Manager setup or downloaded manually by following the manual setup. This release includes changes to the underlying discovery mechanism to allow apps that are built with Xcode 12 to find Cast devices on the network. The Cast button should now always display. If no devices are available when the user taps on the Cast button, a dialog will be displayed providing guidance on why devices may not be available, including information on how to re-enable local-network access permission.

Cast SDK changes

First-time casting

The first time a user attempts to Cast, a local network access (LNA) interstitial dialog will appear explaining why local networking access is needed, followed by the Apple-provided iOS local network access permissions prompt. The mocks below illustrate the flow:

Local network access permissions flow

Cast unavailable

Starting with iOS sender SDK 4.6.0, the Cast button always appears when the user is connected to Wi-Fi. When Cast devices are unavailable, tapping on the Cast button brings up a dialog that gives the user hints as to possible reasons Cast is unavailable, as shown in the mocks below:

Flow with Cast unavailable

Updating your app

Add the Cast iOS SDK 4.8.6 to your project
If using Swift Package Manager, update the google-cast-ios-sdk package to version 4.8.6.

Otherwise, pull in the SDK manually.

Note: If you built a custom device picker in your app, then you will need to explicitly call the startDiscovery method on the GCKDiscoveryManager class to initiate device discovery. Automatic scanning was disabled by default beginning with the v4.5.0 release of the Cast SDK.
Add NSBonjourServices to your Info.plist
Specify NSBonjourServices in your Info.plist to allow local network discovery to succeed.

You will need to add both _googlecast._tcp and _<your-app-id>._googlecast._tcp as services for device discovery to work properly.

The appID is your receiverID, which is the same ID that is defined in your GCKDiscoveryCriteria.

Update the following example NSBonjourServices definition and replace "ABCD1234" with your appID.
```
<key>NSBonjourServices</key>
<array>
  <string>_googlecast._tcp</string>
  <string>_ABCD1234._googlecast._tcp</string>
</array>
```
Add NSLocalNetworkUsageDescription to your Info.plist
We strongly recommend that you customize the message shown in the Local Network prompt by adding an app-specific permission string in your app's Info.plist file for the NSLocalNetworkUsageDescription such as to describe Cast discovery and other discovery services, like DIAL.
```
<key>NSLocalNetworkUsageDescription</key>
<string>${PRODUCT_NAME} uses the local network to discover Cast-enabled devices on your WiFi
network.</string>
```
This message will appear as part of the iOS Local Network Access dialog as shown in the mock.
Re-release your app to the Apple App Store
We recommend you also re-release your app using 4.8.6 as soon as possible.

Customizations

Cast device discovery initiation

By default, Cast device discovery is initiated the first time the user taps the Cast button (GCKUICastButton). If this is the first time the user has attempted to use the Cast app on the local network, the new LNA interstitial will appear, followed by the iOS Local Network Access permissions dialog.

A new flag is available to allow you to control when device discovery starts and the behavior of certain elements of the UX:

startDiscoveryAfterFirstTapOnCastButton: BOOL(true/false)

The default value is true. This flag is only applicable when the flag GCKCastOptions::disableDiscoveryAutostart is set to false.

If set to true, Cast device discovery starts when a user taps on the GCKUICastButton for the first time. An informational message will be displayed to the user letting them know why local network permission is needed. Following that message, the iOS LNA message will be displayed. Cast device discovery starts after the message is acknowledged.

In subsequent App launches, GCKUICastButton always displays.

If set to false, device discovery will start based on the value of the flag GCKCastOptions::disableDiscoveryAutostart.

Frequently asked questions

What happens if I re-release my Cast sender app with the Cast SDK v4.4.8 and Xcode 12?

Your app may not be able to discover Cast devices on the local network unless you have obtained a networking multicast entitlement from Apple. Note that Apple will not be granting multicast entitlements solely for the purpose of supporting Cast. If you plan to build with Xcode 12, you should release your app with Cast 4.6.0.

What will I need to do to update my app once the new version of the Cast SDK is released?

Update your app's Info.plist to include a local network usage description.
Add NSBonjourServices to your app's Info.plist and provide the Bonjour service names for Cast and your app ID.
Upgrade your sender app to use Cast SDK 4.6.0.
Re-release your app to the Apple app store.

Why did devices stop showing up in my custom device picker after I upgraded to 4.6.0?

This is a known issue that can happen if you are using a custom device picker instead of the standard device picker. In version 4.4.8 of the Cast SDK and earlier, device scanning was automatic. Beginning in version 4.6.0, you will need to explicitly call the startDiscovery method on the GCKDiscoveryManager class to initiate device discovery.

The reason for this change is because the Local Network Access (LNA) permissions prompt will appear after the app has scanned for the first time. This could result in permissions dialogs appearing at random places in your app.

Developers who build a custom device picker for their app will be expected to provide an one-time interstitial prior to intiating device scanning for the first time.

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