2024/12/05 18:34:58
添加事件监听
如需收到消息和事件通知,你需要先实现事件监听程序,然后订阅或者加入你想要接收消息或事件通知的频道。
添加事件监听
RTM 采用统一入口的方式处理消息和事件通知,每一种消息和事件通知都有对应的事件处理程序入口,你可以在其中实现自己的业务处理逻辑:
Dart
rtmClient.addListener(
// Handle message event
message: (MessageEvent event) {
const channelType = event.channelType; // The channel type need to be "STREAM" or "MESSAGE".
const channelName = event.channelName; // The name of the channel that this message comes from.
const topicName = event.channelTopic; // (Stream channel only) The name of the topic that this message comes from.
const messageType = event.messageType; // The message type need to be "STRING" or "BINARY".
const customType = event.customType; // User defined type.
const publisher = event.publisher; // Message publisher.
const message = event.message; // Message payload.
const timestamp = event.timestamp; // Message send timestamp.
},
// Handle presence event
presence: (PresenceEvent event) {
const action = event.type; // Which action it is ,should be one of 'SNAPSHOT'、'INTERVAL'、'JOIN'、'LEAVE'、'TIMEOUT、'STATE_CHANGED'、'OUT_OF_SERVICE'.
const channelType = event.channelType; // Which channel type it is, Should be "STREAM" or "MESSAGE".
const channelName = event.channelName; // Which channel does this event come from
const publisher = event.publisher; // Who trigger this event
const states = event.stateItems; // User state payload, only for stateChanged event
const interval = event.interval; // Interval payload, only for interval event
const snapshot = event.snapshot; // Snapshot payload, only for snapshot event
const timestamp = event.timestamp; // event trigger timestamp.
},
// Handle topic event
topic: (TopicEvent event) {
const action = event.type; // Which action it is ,should be one of 'SNAPSHOT'、'JOIN'、'LEAVE'.
const channelName = event.channelName; // Which channel does this event comes from
const publisher = event.publisher; // Who trigger this event
const topicInfos = event.topicInfos; // Topic information payload
const timestamp = event.timestamp; // event trigger timestamp.
},
// Handle storage event
storage: (StorageEvent event) {
const channelType = event.channelType; // Which channel type it is, Should be "STREAM" or "MESSAGE".
const target = event.target; // Which channel or who trigger this event
const storageType = event.storageType; // Which category the event is, should be 'USER'、'CHANNEL'
const action = event.eventType; // Which action it is ,should be one of "SNAPSHOT"、"SET"、"REMOVE"、"UPDATE" or "NONE"
const data = event.data; // 'USER_METADATA' or 'CHANNEL_METADATA' payload
const timestamp = event.timestamp; // event trigger timestamp.
},
// Handle lock event
lock: (LockEvent event) {
const channelType = event.channelType; // Which channel type it is, Should be "STREAM" or "MESSAGE".
const channelName = event.channelName; // Which channel does this event come from
const action = event.evenType; // Which action it is ,should be one of 'SET'、'REMOVED'、'ACQUIRED'、'RELEASED'、'EXPIRED'、'SNAPSHOT'
const lockDetailList = event.lockDetailList; // lock event payload
const timestamp = event.timestamp; // event trigger timestamp.
},
// Handle link state event
linkState: (LinkStateEvent event) {
const currentState = event.currentState; // What is current link state
const previousState = event.previousState; // What is previous link state
const serviceType = event.serviceType; // Which service type it is, Should be "stream" or "message".
const operation = event.operation; // Which operation trigger this state changed
const reason = event.reason; // Which reason trigger this state changed
const affectedChannels = event.affectedChannels; // Which channels are affected
const unrestoredChannels = event.unrestoredChannels; // Which channels are unrestored
const isResumed = event.isResumed;
const timestamp = event.timestamp; // event trigger timestamp.
},
// Handle token event
token : (TokenEvent event) {
const channelName = event.channelName; // Which channel's token token will expire, if it is '', message service token will expire or stream service token will expire
});
消息格式转换
MessageEvent
中的 message
字段为 Uint8List
类型,当你收到字符串类型的消息后,可以使用 dart:convert
库中的 utf8.decode()
方法将其转换成 Srting
类型:
Dart
// convert Uint8List to String. ! means forced conversion
String message = utf8.decode(event.message!);
删除事件监听
为避免内存泄漏、错误和异常(即空指针异常)引起的性能下降,声网建议你在不需要使用某个事件处理程序时对其进行注销。如需注销事件监听程序,则需在添加事件监听时避免采用匿名函数的方式,以下是添加和注销事件监听程序的示例代码。
Dart
// 定义消息时间处理函数
void onMessageReceived(MessageEvent event) {
print('Received message event: $event');
}
// 注册 message event
rtmClient.addListener(
message: onMessageReceived
);
//移除 message event
rtmClient.removeListener(
message: onMessageReceived
);
事件通知类型
RTM 一共有 7 种类型事件,对应的有 7 种事件监听程序。你可以查看 API 参考的事件监听章节,了解每个事件监听程序传入参数的详细信息。
事件监听程序 | 描述 |
---|---|
message | 接收所有订阅的 Message Channel 中的消息通知或你加入的所有 Stream Channel 中订阅的 Topic 消息通知。事件负载数据中包含频道名称、频道类型、Topic 名称、事件发送者、消息负载数据类型等信息。 |
presence | 接收所有订阅的 Message Channel 或者你加入的所有 Stream Channel 中远端用户的在线状态事件通知。事件负载数据中包含频道名称、频道类型、事件类型、事件发送者、用户临时状态数据等信息。 |
topic | 接收加入的所有 Stream Channel 中 Topic 变更事件通知。事件负载数据中包含频道名称、事件类型、Topic 名称、事件发送者(即 Topic 详情)等信息。 |
storage | 接收订阅的 Message Channel 及加入的 Stream Channel 中所有的 Channel Metadata 事件通知,以及所有订阅用户的 User Metadata 事件通知。事件负载数据中包含频道名称、频道类型、事件类型(即具体 Metadata 数据)等信息。 |
lock | 接收订阅的 Message Channel 及加入的 Stream Channel 中所有的 Lock 事件通知。事件负载数据中包含有频道名称、频道类型、事件类型、锁详情等信息。 |
linkState | 接收客户端网络连接状态变更的事件通知,包含变更前后的连接状态、服务类型、导致变更的操作类型、变更原因、频道列表等信息。 |
token | 接收客户端 Token 将要过期的事件通知。 |
完成事件监听处理程序后,你可以通过订阅频道或 Topic 来接收指定的 Message Channel 或 Stream Channel 中的消息和事件通知了。详见订阅 Message Channel 和订阅 Topic。