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serverpod-server-events

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Serverpod Server Events

Serverpod Server Events

Event messaging via 
session.messages
on named channels. Messages must be serializable models. By default (
MessageScope.auto
) messages are delivered across the cluster when Redis is enabled, otherwise locally within the server instance.
通过
session.messages
在命名通道上进行事件消息传递。消息必须是可序列化的模型。默认情况下（
MessageScope.auto
），当Redis启用时，消息会在集群间传递，否则仅在服务器实例本地传递。

Sending

发送消息

dart
await session.messages.postMessage('user_updates', UserUpdate(...));

// Restrict delivery with a scope:
await session.messages.postMessage('user_updates', message, scope: MessageScope.local);
await session.messages.postMessage('user_updates', message, scope: MessageScope.global);
MessageScope.local
delivers synchronously within this server only. 
MessageScope.global
requires Redis and throws a 
StateError
if it is not enabled. With Redis enabled, delivery is asynchronous and best effort, and listeners receive a deserialized copy of the message rather than the posted instance.
dart
await session.messages.postMessage('user_updates', UserUpdate(...));

// 通过作用域限制消息传递范围：
await session.messages.postMessage('user_updates', message, scope: MessageScope.local);
await session.messages.postMessage('user_updates', message, scope: MessageScope.global);
MessageScope.local
仅在当前服务器内同步传递消息。
MessageScope.global
需要Redis支持，如果未启用Redis会抛出
StateError
。当Redis启用时，消息传递是异步且尽力而为的，监听器会接收消息的反序列化副本而非发布的实例。

Receiving

接收消息

Stream:
dart
var stream = session.messages.createStream<UserUpdate>('user_updates');
stream.listen((message) => print('Received: $message'));
If a message on the channel is not of type 
T
, the stream emits an error. Use exact serializable types or a deliberate shared base type.
Listener:
dart
session.messages.addListener<UserUpdate>('user_updates', (message) {
  print('Received: $message');
});
Both receive local and global messages. Streams/listeners are removed when the session closes. Remove manually with 
session.messages.removeListener(channel, callback)
. Models support inheritance, which is useful when wanting a fully typed interface for server events.
流方式：
dart
var stream = session.messages.createStream<UserUpdate>('user_updates');
stream.listen((message) => print('Received: $message'));
如果通道中的消息类型不是
T
，流会抛出错误。请使用精确的可序列化类型或明确的共享基类。
监听器方式：
dart
session.messages.addListener<UserUpdate>('user_updates', (message) {
  print('Received: $message');
});
两种方式都会接收本地和全局消息。当会话关闭时，流/监听器会被自动移除。也可以通过
session.messages.removeListener(channel, callback)
手动移除。模型支持继承，这在为服务器事件提供全类型化接口时非常有用。