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向主题发送消息（Apple 平台）

基于其发布/订阅的模式，FCM 主题消息传递功能可让您将消息发送至已经选择加入特定主题的多台设备。您只需根据需要撰写主题消息，FCM 会负责确定发送路径并将消息可靠地传送至正确的设备。

例如，某个本地潮汐预报应用的用户可选择订阅“潮汐提醒”主题，并接收关于特定区域最佳海洋捕鱼条件的通知。体育应用的用户可以订阅他们心仪球队的实时比分自动更新。

关于主题，请注意以下事项：

主题消息传递最适合的内容是天气等可通过公开途径获得的信息。
主题消息的优化重心是吞吐量而非延迟。如需将消息快速安全地传送到单台设备或小规模设备组，应将消息定位至注册令牌而非主题。
如果您需要向一个用户的多台设备发送消息，请考虑在这些使用场景中使用设备组消息传递。
主题消息传递不限制每个主题的订阅数。但是，FCM 在以下方面有强制性限制：
- 一个应用实例最多只能订阅 2,000 个主题。
- 如果您通过批量导入来订阅应用实例，则每次请求仅限订阅 1,000 个应用实例。
- 每个项目新增订阅的频率存在限制。如果您在短时间内发送过多订阅请求，FCM 服务器将给出 429 RESOURCE_EXHAUSTED（“已超出配额”）响应。请使用指数退避算法重试。

为客户端应用订阅主题

客户端应用可以订阅任何现有主题，也可以创建新主题。当客户端应用订阅新的主题名称（您的 Firebase 项目中尚不存在的主题）时，系统会在 FCM 中创建一个以该名称命名的新主题，此后任何客户端都可订阅该主题。

如需订阅一个主题，请从应用的主线程中调用订阅方法（FCM 并不保证线程安全性）。如果初始订阅请求失败，FCM 会自动重试。对于无法完成订阅的情况，订阅会抛出一个错误，您可以在完成处理程序中捕获该错误，如下所示：

Swift

Messaging.messaging().subscribe(toTopic: "weather") { error in
  print("Subscribed to weather topic")
}ViewController.swift

Objective-C

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

此调用会向 FCM 后端发出一个异步请求，并为该客户端订阅指定主题。在调用 subscribeToTopic:topic 之前，请确保客户端应用实例已通过回调函数 didReceiveRegistrationToken 收到注册令牌。

每次应用启动时，FCM 会确保请求的所有主题都已订阅。如需退订主题，请调用 unsubscribeFromTopic:topic，FCM 即会在后台中退订相关主题。

在服务器上管理主题订阅

借助 Firebase Admin SDK，您可以从服务器端执行基本的主题管理任务。如果有客户端应用实例的注册令牌，您还可以使用服务器逻辑批量订阅和退订这些实例。

您可以为客户端应用实例订阅任何现有主题，也可创建新主题。当您使用 API 为客户端应用订阅新主题（您的 Firebase 项目中尚不存在的主题）时，系统会在 FCM 中创建一个使用该名称的新主题，此后任何客户端都可订阅该主题。

您可以将一个注册令牌列表传递给 Firebase Admin SDK 订阅方法，以便为相应的设备订阅主题：

Node.js

// These registration tokens come from the client FCM SDKs.
const registrationTokens = [
  'YOUR_REGISTRATION_TOKEN_1',
  // ...
  'YOUR_REGISTRATION_TOKEN_n'
];

// Subscribe the devices corresponding to the registration tokens to the
// topic.
getMessaging().subscribeToTopic(registrationTokens, topic)
  .then((response) => {
    // See the MessagingTopicManagementResponse reference documentation
    // for the contents of response.
    console.log('Successfully subscribed to topic:', response);
  })
  .catch((error) => {
    console.log('Error subscribing to topic:', error);
  });

Java

// These registration tokens come from the client FCM SDKs.
List<String> registrationTokens = Arrays.asList(
    "YOUR_REGISTRATION_TOKEN_1",
    // ...
    "YOUR_REGISTRATION_TOKEN_n"
);

// Subscribe the devices corresponding to the registration tokens to the
// topic.
TopicManagementResponse response = FirebaseMessaging.getInstance().subscribeToTopic(
    registrationTokens, topic);
// See the TopicManagementResponse reference documentation
// for the contents of response.
System.out.println(response.getSuccessCount() + " tokens were subscribed successfully");

Python

# These registration tokens come from the client FCM SDKs.
registration_tokens = [
    'YOUR_REGISTRATION_TOKEN_1',
    # ...
    'YOUR_REGISTRATION_TOKEN_n',
]

# Subscribe the devices corresponding to the registration tokens to the
# topic.
response = messaging.subscribe_to_topic(registration_tokens, topic)
# See the TopicManagementResponse reference documentation
# for the contents of response.
print(response.success_count, 'tokens were subscribed successfully')

Go

// These registration tokens come from the client FCM SDKs.
registrationTokens := []string{
	"YOUR_REGISTRATION_TOKEN_1",
	// ...
	"YOUR_REGISTRATION_TOKEN_n",
}

// Subscribe the devices corresponding to the registration tokens to the
// topic.
response, err := client.SubscribeToTopic(ctx, registrationTokens, topic)
if err != nil {
	log.Fatalln(err)
}
// See the TopicManagementResponse reference documentation
// for the contents of response.
fmt.Println(response.SuccessCount, "tokens were subscribed successfully")

C#

// These registration tokens come from the client FCM SDKs.
var registrationTokens = new List<string>()
{
    "YOUR_REGISTRATION_TOKEN_1",
    // ...
    "YOUR_REGISTRATION_TOKEN_n",
};

// Subscribe the devices corresponding to the registration tokens to the
// topic
var response = await FirebaseMessaging.DefaultInstance.SubscribeToTopicAsync(
    registrationTokens, topic);
// See the TopicManagementResponse reference documentation
// for the contents of response.
Console.WriteLine($"{response.SuccessCount} tokens were subscribed successfully");FirebaseMessagingSnippets.cs

利用 Admin FCM API，您还可以将注册令牌传递给相应的方法，来为设备退订主题：

Node.js

// These registration tokens come from the client FCM SDKs.
const registrationTokens = [
  'YOUR_REGISTRATION_TOKEN_1',
  // ...
  'YOUR_REGISTRATION_TOKEN_n'
];

// Unsubscribe the devices corresponding to the registration tokens from
// the topic.
getMessaging().unsubscribeFromTopic(registrationTokens, topic)
  .then((response) => {
    // See the MessagingTopicManagementResponse reference documentation
    // for the contents of response.
    console.log('Successfully unsubscribed from topic:', response);
  })
  .catch((error) => {
    console.log('Error unsubscribing from topic:', error);
  });

Java

// These registration tokens come from the client FCM SDKs.
List<String> registrationTokens = Arrays.asList(
    "YOUR_REGISTRATION_TOKEN_1",
    // ...
    "YOUR_REGISTRATION_TOKEN_n"
);

// Unsubscribe the devices corresponding to the registration tokens from
// the topic.
TopicManagementResponse response = FirebaseMessaging.getInstance().unsubscribeFromTopic(
    registrationTokens, topic);
// See the TopicManagementResponse reference documentation
// for the contents of response.
System.out.println(response.getSuccessCount() + " tokens were unsubscribed successfully");

Python

# These registration tokens come from the client FCM SDKs.
registration_tokens = [
    'YOUR_REGISTRATION_TOKEN_1',
    # ...
    'YOUR_REGISTRATION_TOKEN_n',
]

# Unubscribe the devices corresponding to the registration tokens from the
# topic.
response = messaging.unsubscribe_from_topic(registration_tokens, topic)
# See the TopicManagementResponse reference documentation
# for the contents of response.
print(response.success_count, 'tokens were unsubscribed successfully')

Go

// These registration tokens come from the client FCM SDKs.
registrationTokens := []string{
	"YOUR_REGISTRATION_TOKEN_1",
	// ...
	"YOUR_REGISTRATION_TOKEN_n",
}

// Unsubscribe the devices corresponding to the registration tokens from
// the topic.
response, err := client.UnsubscribeFromTopic(ctx, registrationTokens, topic)
if err != nil {
	log.Fatalln(err)
}
// See the TopicManagementResponse reference documentation
// for the contents of response.
fmt.Println(response.SuccessCount, "tokens were unsubscribed successfully")

C#

// These registration tokens come from the client FCM SDKs.
var registrationTokens = new List<string>()
{
    "YOUR_REGISTRATION_TOKEN_1",
    // ...
    "YOUR_REGISTRATION_TOKEN_n",
};

// Unsubscribe the devices corresponding to the registration tokens from the
// topic
var response = await FirebaseMessaging.DefaultInstance.UnsubscribeFromTopicAsync(
    registrationTokens, topic);
// See the TopicManagementResponse reference documentation
// for the contents of response.
Console.WriteLine($"{response.SuccessCount} tokens were unsubscribed successfully");FirebaseMessagingSnippets.cs

subscribeToTopic() 和 unsubscribeFromTopic() 方法会返回一个包含 FCM 响应的对象。无论请求中指定的注册令牌的数量是多少，返回类型的格式都是相同的。

如果出现错误（身份验证失败、令牌或主题无效等），这些方法也会返回错误。如需查看错误代码的完整列表（包括说明和解决步骤），请参阅 Admin FCM API 错误。

接收和处理主题消息

FCM 传送主题消息的方式与传送其他下行消息的方式相同。

如下所示，实现 application(_:didReceiveRemoteNotification:fetchCompletionHandler:)：

Swift

func application(_ application: UIApplication,
                 didReceiveRemoteNotification userInfo: [AnyHashable: Any]) async
  -> UIBackgroundFetchResult {
  // 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)

  return UIBackgroundFetchResult.newData
}
AppDelegate.swift

Objective-C

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

  completionHandler(UIBackgroundFetchResultNewData);
}AppDelegate.m

构建发送请求

创建主题后，您可以通过两种方法向主题发送消息：一种是在客户端为客户端应用实例订阅该主题，另一种是使用服务器 API。如果您是首次构建 FCM 发送请求，请参阅关于您的服务器环境和 FCM 的指南，了解重要的背景信息和设置信息。

在后端的发送逻辑中，按如下所述的方式指定所需的主题名称：

Node.js

// The topic name can be optionally prefixed with "/topics/".
const topic = 'highScores';

const message = {
  data: {
    score: '850',
    time: '2:45'
  },
  topic: topic
};

// Send a message to devices subscribed to the provided topic.
getMessaging().send(message)
  .then((response) => {
    // Response is a message ID string.
    console.log('Successfully sent message:', response);
  })
  .catch((error) => {
    console.log('Error sending message:', error);
  });

Java

// The topic name can be optionally prefixed with "/topics/".
String topic = "highScores";

// See documentation on defining a message payload.
Message message = Message.builder()
    .putData("score", "850")
    .putData("time", "2:45")
    .setTopic(topic)
    .build();

// Send a message to the devices subscribed to the provided topic.
String response = FirebaseMessaging.getInstance().send(message);
// Response is a message ID string.
System.out.println("Successfully sent message: " + response);FirebaseMessagingSnippets.java

Python

# The topic name can be optionally prefixed with "/topics/".
topic = 'highScores'

# See documentation on defining a message payload.
message = messaging.Message(
    data={
        'score': '850',
        'time': '2:45',
    },
    topic=topic,
)

# Send a message to the devices subscribed to the provided topic.
response = messaging.send(message)
# Response is a message ID string.
print('Successfully sent message:', response)cloud_messaging.py

Go

// The topic name can be optionally prefixed with "/topics/".
topic := "highScores"

// See documentation on defining a message payload.
message := &messaging.Message{
	Data: map[string]string{
		"score": "850",
		"time":  "2:45",
	},
	Topic: topic,
}

// Send a message to the devices subscribed to the provided topic.
response, err := client.Send(ctx, message)
if err != nil {
	log.Fatalln(err)
}
// Response is a message ID string.
fmt.Println("Successfully sent message:", response)messaging.go

C#

// The topic name can be optionally prefixed with "/topics/".
var topic = "highScores";

// See documentation on defining a message payload.
var message = new Message()
{
    Data = new Dictionary<string, string>()
    {
        { "score", "850" },
        { "time", "2:45" },
    },
    Topic = topic,
};

// Send a message to the devices subscribed to the provided topic.
string response = await FirebaseMessaging.DefaultInstance.SendAsync(message);
// Response is a message ID string.
Console.WriteLine("Successfully sent message: " + response);

REST

POST https://fcm.googleapis.com/v1/projects/myproject-b5ae1/messages:send HTTP/1.1

Content-Type: application/json
Authorization: Bearer ya29.ElqKBGN2Ri_Uz...HnS_uNreA
{
  "message":{
    "topic" : "foo-bar",
    "notification" : {
      "body" : "This is a Firebase Cloud Messaging Topic Message!",
      "title" : "FCM Message"
      }
   }
}

cURL 命令：

curl -X POST -H "Authorization: Bearer ya29.ElqKBGN2Ri_Uz...HnS_uNreA" -H "Content-Type: application/json" -d '{
  "message": {
    "topic" : "foo-bar",
    "notification": {
      "body": "This is a Firebase Cloud Messaging Topic Message!",
      "title": "FCM Message"
    }
  }
}' https://fcm.googleapis.com/v1/projects/myproject-b5ae1/messages:send HTTP/1.1

如需向主题组合发送消息，请指定一个条件，该条件是一个指定目标主题的布尔表达式。例如，如需向既订阅了 TopicA，又订阅了 TopicB 或 TopicC 的设备发送消息，请设置如下条件：

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

FCM 首先对括号中的所有条件求值，然后从左至右对表达式求值。在上述表达式中，只订阅了其中某个主题的用户将不会接收到消息。同样地，未订阅 TopicA 的用户也不会接收到消息。订阅下列组合的用户才会接收到消息：

TopicA 和 TopicB
TopicA 和 TopicC

您最多可以在条件表达式中包含五个主题。

根据条件发送消息：

Node.js

// Define a condition which will send to devices which are subscribed
// to either the Google stock or the tech industry topics.
const condition = '\'stock-GOOG\' in topics || \'industry-tech\' in topics';

// See documentation on defining a message payload.
const message = {
  notification: {
    title: '$FooCorp up 1.43% on the day',
    body: '$FooCorp gained 11.80 points to close at 835.67, up 1.43% on the day.'
  },
  condition: condition
};

// Send a message to devices subscribed to the combination of topics
// specified by the provided condition.
getMessaging().send(message)
  .then((response) => {
    // Response is a message ID string.
    console.log('Successfully sent message:', response);
  })
  .catch((error) => {
    console.log('Error sending message:', error);
  });

Java

// Define a condition which will send to devices which are subscribed
// to either the Google stock or the tech industry topics.
String condition = "'stock-GOOG' in topics || 'industry-tech' in topics";

// See documentation on defining a message payload.
Message message = Message.builder()
    .setNotification(Notification.builder()
        .setTitle("$GOOG up 1.43% on the day")
        .setBody("$GOOG gained 11.80 points to close at 835.67, up 1.43% on the day.")
        .build())
    .setCondition(condition)
    .build();

// Send a message to devices subscribed to the combination of topics
// specified by the provided condition.
String response = FirebaseMessaging.getInstance().send(message);
// Response is a message ID string.
System.out.println("Successfully sent message: " + response);FirebaseMessagingSnippets.java

Python

# Define a condition which will send to devices which are subscribed
# to either the Google stock or the tech industry topics.
condition = "'stock-GOOG' in topics || 'industry-tech' in topics"

# See documentation on defining a message payload.
message = messaging.Message(
    notification=messaging.Notification(
        title='$GOOG up 1.43% on the day',
        body='$GOOG gained 11.80 points to close at 835.67, up 1.43% on the day.',
    ),
    condition=condition,
)

# Send a message to devices subscribed to the combination of topics
# specified by the provided condition.
response = messaging.send(message)
# Response is a message ID string.
print('Successfully sent message:', response)cloud_messaging.py

Go

// Define a condition which will send to devices which are subscribed
// to either the Google stock or the tech industry topics.
condition := "'stock-GOOG' in topics || 'industry-tech' in topics"

// See documentation on defining a message payload.
message := &messaging.Message{
	Data: map[string]string{
		"score": "850",
		"time":  "2:45",
	},
	Condition: condition,
}

// Send a message to devices subscribed to the combination of topics
// specified by the provided condition.
response, err := client.Send(ctx, message)
if err != nil {
	log.Fatalln(err)
}
// Response is a message ID string.
fmt.Println("Successfully sent message:", response)messaging.go

C#

// Define a condition which will send to devices which are subscribed
// to either the Google stock or the tech industry topics.
var condition = "'stock-GOOG' in topics || 'industry-tech' in topics";

// See documentation on defining a message payload.
var message = new Message()
{
    Notification = new Notification()
    {
        Title = "$GOOG up 1.43% on the day",
        Body = "$GOOG gained 11.80 points to close at 835.67, up 1.43% on the day.",
    },
    Condition = condition,
};

// Send a message to devices subscribed to the combination of topics
// specified by the provided condition.
string response = await FirebaseMessaging.DefaultInstance.SendAsync(message);
// Response is a message ID string.
Console.WriteLine("Successfully sent message: " + response);

REST

POST https://fcm.googleapis.com/v1/projects/myproject-b5ae1/messages:send HTTP/1.1

Content-Type: application/json
Authorization: Bearer ya29.ElqKBGN2Ri_Uz...HnS_uNreA
{
   "message":{
    "condition": "'dogs' in topics || 'cats' in topics",
    "notification" : {
      "body" : "This is a Firebase Cloud Messaging Topic Message!",
      "title" : "FCM Message",
    }
  }
}

cURL 命令：

curl -X POST -H "Authorization: Bearer ya29.ElqKBGN2Ri_Uz...HnS_uNreA" -H "Content-Type: application/json" -d '{
  "notification": {
    "title": "FCM Message",
    "body": "This is a Firebase Cloud Messaging Topic Message!",
  },
  "condition": "'dogs' in topics || 'cats' in topics"
}' https://fcm.googleapis.com/v1/projects/myproject-b5ae1/messages:send HTTP/1.1

后续步骤

详细了解向多台设备发送消息的另一种方式 - 设备组消息传递