Send Messages to Multiple Devices

Firebase Cloud Messaging provides two ways to target a message to multiple devices:

  • Topic messaging, which allows you to send a message to multiple devices that have opted in to a particular topic.
  • Device group messaging, which allows you to send a single message to multiple instances of an app running on devices belonging to a group.

This tutorial focuses on sending topic messages from your app server using the HTTP or XMPP protocols for FCM, and receiving and handling them in an iOS app. This page lists all the steps to achieve this, from setup to verification — so it may cover steps you already completed if you have set up an iOS client app for FCM or worked through the steps to Send your First Message.

Add Firebase to your iOS project

This section covers tasks you may have completed if you have already enabled other Firebase features for your app. For FCM specifically, you'll need to upload your APNs authentication key and register for remote notifications.

Prerequisites

Before you begin, you need a few things set up in your environment:

  • Xcode 9.0 or later
  • An Xcode project targeting iOS 8 or above
  • Swift projects must use Swift 3.0 or later
  • The bundle identifier of your app
  • CocoaPods 1.4.0 or later
  • For Cloud Messaging:
    • A physical iOS device
    • An Apple Push Notification Authentication Key for your Apple Developer account
    • In Xcode, enable Push Notifications in App > Capabilities

If you don't have an Xcode project already, you can download one of our quickstart samples if you just want to try a Firebase feature. If you're using a quickstart, remember to get the bundle identifier from the project settings, you'll need it for the next step.

Add Firebase to your app

It's time to add Firebase to your app. To do this you'll need a Firebase project and a Firebase configuration file for your app.

To create a Firebase project:

  1. Create a Firebase project in the Firebase console, if you don't already have one. Click Add project. If you already have an existing Google project associated with your mobile app, select it from the Project name drop down menu. Otherwise, enter a project name to create a new project.
  2. Optional: Edit your Project ID. Your project is given a unique ID automatically, and it's used in publicly visible Firebase features such as database URLs and your Firebase Hosting subdomain. You can change it now if you want to use a specific subdomain.
  3. Follow the remaining setup steps and click Create project (or Add Firebase if you're using an existing project) to begin provisioning resources for your project. This typically takes a few minutes. When the process completes, you'll be taken to the project overview.

Now that you have a project, you can add your iOS app to it:

  1. Click Add Firebase to your iOS app and follow the setup steps. If you're importing an existing Google project, this may happen automatically and you can just download the config file.
  2. When prompted, enter your app's bundle ID. It's important to enter the bundle ID your app is using; this can only be set when you add an app to your Firebase project.
  3. During the process, you'll download a GoogleService-Info.plist file. You can download this file again at any time.
  4. After you add the initialization code, run your app to send verification to the Firebase console that you've successfully installed Firebase.

Add the SDK

If you are setting up a new project, you need to install the SDK. You may have already completed this as part of creating a Firebase project.

We recommend using CocoaPods to install the libraries. You can install Cocoapods by following the installation instructions. If you'd rather not use CocoaPods, you can integrate the SDK frameworks directly without using CocoaPods.

If you are planning to download and run one of the quickstart samples, the Xcode project and Podfile are already present, but you'll still need to install the pods and download the GoogleService-Info.plist file. If you would like to integrate the Firebase libraries into one of your own projects, you will need to add the pods for the libraries that you want to use.

  1. If you don't have an Xcode project yet, create one now.

  2. Create a Podfile if you don't have one:

    $ cd your-project directory
    $ pod init
    
  3. Add the pods that you want to install. You can include a Pod in your Podfile like this:

    pod 'Firebase/Core'
    pod 'Firebase/Messaging'
    

    This will add the prerequisite libraries needed to get Firebase up and running in your iOS app, along with Google Analytics for Firebase. A list of currently available pods and subspecs is provided below. These are linked in feature specific setup guides as well.

  4. Install the pods and open the .xcworkspace file to see the project in Xcode.

    $ pod install
    $ open your-project.xcworkspace
    
  5. Download a GoogleService-Info.plist file from Firebase console and include it in your app.

Upload your APNs authentication key

Upload your APNs authentication key to Firebase. If you don't already have an APNs authentication key, see Configuring APNs with FCM.

  1. Inside your project in the Firebase console, select the gear icon, select Project Settings, and then select the Cloud Messaging tab.

  2. In APNs authentication key under iOS app configuration, click the Upload button.

  3. Browse to the location where you saved your key, select it, and click Open. Add the key ID for the key (available in Certificates, Identifiers & Profiles in the Apple Developer Member Center) and click Upload.

Initialize Firebase in your app

You'll need to add Firebase initialization code to your application. Import the Firebase module and configure a shared instance as shown:

  1. Import the Firebase module in your UIApplicationDelegate:

    Swift

    import Firebase
    

    Objective-C

    @import Firebase;
    
  2. Configure a FirebaseApp shared instance, typically in your application's application:didFinishLaunchingWithOptions: method:

    Swift

    // Use Firebase library to configure APIs
    FirebaseApp.configure()
    

    Objective-C

    // Use Firebase library to configure APIs
    [FIRApp configure];
    

Register for remote notifications

Either at startup, or at the desired point in your application flow, register your app for remote notifications. Call registerForRemoteNotifications as shown:

Swift

if #available(iOS 10.0, *) {
  // For iOS 10 display notification (sent via APNS)
  UNUserNotificationCenter.current().delegate = self

  let authOptions: UNAuthorizationOptions = [.alert, .badge, .sound]
  UNUserNotificationCenter.current().requestAuthorization(
    options: authOptions,
    completionHandler: {_, _ in })
} else {
  let settings: UIUserNotificationSettings =
  UIUserNotificationSettings(types: [.alert, .badge, .sound], categories: nil)
  application.registerUserNotificationSettings(settings)
}

application.registerForRemoteNotifications()

Objective-C

if ([UNUserNotificationCenter class] != nil) {
  // iOS 10 or later
  // For iOS 10 display notification (sent via APNS)
  [UNUserNotificationCenter currentNotificationCenter].delegate = self;
  UNAuthorizationOptions authOptions = UNAuthorizationOptionAlert |
      UNAuthorizationOptionSound | UNAuthorizationOptionBadge;
  [[UNUserNotificationCenter currentNotificationCenter]
      requestAuthorizationWithOptions:authOptions
      completionHandler:^(BOOL granted, NSError * _Nullable error) {
        // ...
      }];
} else {
  // iOS 10 notifications aren't available; fall back to iOS 8-9 notifications.
  UIUserNotificationType allNotificationTypes =
  (UIUserNotificationTypeSound | UIUserNotificationTypeAlert | UIUserNotificationTypeBadge);
  UIUserNotificationSettings *settings =
  [UIUserNotificationSettings settingsForTypes:allNotificationTypes categories:nil];
  [application registerUserNotificationSettings:settings];
}

[application registerForRemoteNotifications];

Subscribe the client app to a topic

Client apps can subscribe to any existing topic, or they can create a new topic. When a client app subscribes to a new topic name (one that does not already exist for your Firebase project), a new topic of that name is created in FCM and any client can subsequently subscribe to it.

The FIRMessaging class handles topic messaging functionality. To subscribe to a topic, call subscribeToTopic:topic from your application's main thread (FCM is not thread-safe). If the subscription request fails initially, FCM retries automatically. For cases where the subscription cannot be completed, subscribeToTopic:topic throws an error that you can catch in a completion handler as shown:

[[FIRMessaging messaging] subscribeToTopic:@"news"
                                completion:^(NSError * _Nullable error) {
  NSLog(@"Subscribed to news topic");
}];

This call makes an asynchronous request to the FCM backend and subscribes the client to the given topic. Before calling subscribeToTopic:topic, make sure that the client app instance has already received a registration token via the callback didReceiveRegistrationToken.

Each time the app starts, FCM makes sure that all requested topics have been subscribed. To unsubscribe, call unsubscribeFromTopic:topic, and FCM unsubscribes from the topic in the background.

Receive and handle topic messages

FCM delivers topic messages in the same way as other downstream messages.

Implement AppDelegate application:didReceiveRemoteNotification: as shown:

Swift

func application(_ application: UIApplication, didReceiveRemoteNotification userInfo: [AnyHashable: Any]) {
  // If you are receiving a notification message while your app is in the background,
  // this callback will not be fired till the user taps on the notification launching the application.
  // TODO: Handle data of notification

  // With swizzling disabled you must let Messaging know about the message, for Analytics
  // Messaging.messaging().appDidReceiveMessage(userInfo)

  // Print message ID.
  if let messageID = userInfo[gcmMessageIDKey] {
    print("Message ID: \(messageID)")
  }

  // Print full message.
  print(userInfo)
}

func application(_ application: UIApplication, didReceiveRemoteNotification userInfo: [AnyHashable: Any],
                 fetchCompletionHandler completionHandler: @escaping (UIBackgroundFetchResult) -> Void) {
  // If you are receiving a notification message while your app is in the background,
  // this callback will not be fired till the user taps on the notification launching the application.
  // TODO: Handle data of notification

  // With swizzling disabled you must let Messaging know about the message, for Analytics
  // Messaging.messaging().appDidReceiveMessage(userInfo)

  // Print message ID.
  if let messageID = userInfo[gcmMessageIDKey] {
    print("Message ID: \(messageID)")
  }

  // Print full message.
  print(userInfo)

  completionHandler(UIBackgroundFetchResult.newData)
}

Objective-C

- (void)application:(UIApplication *)application didReceiveRemoteNotification:(NSDictionary *)userInfo {
  // If you are receiving a notification message while your app is in the background,
  // this callback will not be fired till the user taps on the notification launching the application.
  // TODO: Handle data of notification

  // With swizzling disabled you must let Messaging know about the message, for Analytics
  // [[FIRMessaging messaging] appDidReceiveMessage:userInfo];

  // Print message ID.
  if (userInfo[kGCMMessageIDKey]) {
    NSLog(@"Message ID: %@", userInfo[kGCMMessageIDKey]);
  }

  // Print full message.
  NSLog(@"%@", userInfo);
}

- (void)application:(UIApplication *)application didReceiveRemoteNotification:(NSDictionary *)userInfo
    fetchCompletionHandler:(void (^)(UIBackgroundFetchResult))completionHandler {
  // If you are receiving a notification message while your app is in the background,
  // this callback will not be fired till the user taps on the notification launching the application.
  // TODO: Handle data of notification

  // With swizzling disabled you must let Messaging know about the message, for Analytics
  // [[FIRMessaging messaging] appDidReceiveMessage:userInfo];

  // Print message ID.
  if (userInfo[kGCMMessageIDKey]) {
    NSLog(@"Message ID: %@", userInfo[kGCMMessageIDKey]);
  }

  // Print full message.
  NSLog(@"%@", userInfo);

  completionHandler(UIBackgroundFetchResultNewData);
}

Build send requests

Sending messages to a Firebase Cloud Messaging topic is very similar to sending messages to an individual device or to a user group. The app server sets the to key with a value like /topics/yourTopic. Developers can choose any topic name that matches the regular expression: "/topics/[a-zA-Z0-9-_.~%]+".

To send to combinations of multiple topics, the app server must set the condition key (instead of the to key) to a boolean condition that specifies the target topics. For example, to send messages to devices that subscribed to TopicA and either TopicB or TopicC:

'TopicA' in topics && ('TopicB' in topics || 'TopicC' in topics)

FCM first evaluates any conditions in parentheses, and then evaluates the expression from left to right. In the above expression, a user subscribed to any single topic does not receive the message. Likewise, a user who does not subscribe to TopicA does not receive the message. These combinations do receive it:

  • TopicA and TopicB
  • TopicA and TopicC

You can include up to five topics in your conditional expression, and parentheses are supported. Supported operators: &&, ||, !. Note the usage for !:

!('TopicA' in topics)

With this expression, any app instances that are not subscribed to TopicA, including app instances that are not subscribed to any topic, receive the message.

For more detail about app server keys, see the reference information for your chosen connection server protocol, HTTP or XMPP. Examples in this page show how to send messages to topics in both HTTP and XMPP.

Topic HTTP POST request

Send to a single topic:

https://fcm.googleapis.com/fcm/send
Content-Type:application/json
Authorization:key=AIzaSyZ-1u...0GBYzPu7Udno5aA

{
  "to" : /topics/foo-bar",
  "priority" : "high",
  "notification" : {
    "body" : "This is a Firebase Cloud Messaging Topic Message!",
    "title" : "FCM Message",
  }
}

Send to devices subscribed to topics "dogs" or "cats":

https://fcm.googleapis.com/fcm/send
Content-Type:application/json
Authorization:key=AIzaSyZ-1u...0GBYzPu7Udno5aA

{
  "condition": "'dogs' in topics || 'cats' in topics",
  "priority" : "high",
  "notification" : {
    "body" : "This is a Firebase Cloud Messaging Topic Message!",
    "title" : "FCM Message",
  }
}

Topic HTTP response

//Success example:
{
  "message_id": "1023456"
}

//failure example:
{
  "error": "TopicsMessageRateExceeded"
}

Topic XMPP message

Send to a single topic:

<message id="">
  <gcm xmlns="google:mobile:data">

{
  "to" : /topics/foo-bar",
  "priority" : "high",
  "notification" : {
    "body" : "This is a Firebase Cloud Messaging Topic Message!",
    "title" : "FCM Message",
  }
}
  </gcm>
</message>

Send to devices subscribed to topics "dogs" or "cats":

<message id="">
  <gcm xmlns="google:mobile:data">

{
  "condition": "'dogs' in topics || 'cats' in topics",
  "priority" : "high",
  "notification" : {
    "body" : "This is a Firebase Cloud Messaging Topic Message!",
    "title" : "FCM Message",
  }
}
  </gcm>
</message>

Topic XMPP response

//Success example:
{
  "message_id": "1023456"
}

//failure example:
{
  "error": "TopicsMessageRateExceeded"
}

Expect up to 30 seconds of delay before the FCM Server returns a success or failure response to the topic send requests. Make sure to set the app server's timeout value in the request accordingly.

For the full list of message options, see the reference information for your chosen connection server protocol, HTTP or XMPP.

Next steps

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