[英]Angular Observables return anonymous function
I have this method that I copied from a websocket tutorial but I don't understand the meaning of the "return () => { ... }" inside the observable ?我有这个方法是从 websocket 教程中复制的,但我不明白 observable 中“return () => { ... }”的含义? Can someone explain me what is the purpose of that ?
有人可以解释我这样做的目的是什么吗?
public onMessage(topic: string, handler = SocketClientService.jsonHandler) : Observable<any> {
return this.connect().pipe(first(), switchMap(client => {
return new Observable<any>(observer => {
const subscription : StompSubscription = client.subscribe(topic, message => {
observer.next(handler(message));
});
return () => {
console.log("Unsubscribe from socket-client service");
client.unsubscribe(subscription .id);
}
});
}));
}
In order to create an Observable, you can use new Observable
or a creation operator.为了创建一个 Observable,你可以使用
new Observable
或创建操作符。 See the following example:请参阅以下示例:
const observable = new Observable(function subscribe(subscriber) {
subscriber.next(1);
subscriber.next(2);
subscriber.next(3);
});
You can provide a function unsubscribe()
to allow dispose of resources, and that function goes inside subscribe()
as follows:您可以提供一个函数
unsubscribe()
来允许处理资源,该函数在subscribe()
内部如下:
const observable = new Observable(function subscribe(subscriber) {
subscriber.next(1);
subscriber.next(2);
subscriber.next(3);
return function unsubscribe() {
console.log('Clearing resources on observable');
};
});
Of course, you can use an arrow function expression to have:当然,您可以使用箭头函数表达式来获得:
const observable = new Observable((observer) => {
observer.next(1);
observer.next(2);
observer.next(3);
return () => {
console.log('Clearing resources on observable');
};
});
Try the following code to test the Observable:尝试使用以下代码来测试 Observable:
const subscription = observable.subscribe(res => console.log('observable data:', res));
subscription.unsubscribe();
Finally, subscription.unsubscribe()
is going to remove the socket connection in your example.最后,
subscription.unsubscribe()
将删除示例中的套接字连接。
Find a project running with these examples here: https://stackblitz.com/edit/typescript-observable-unsubscribe在此处查找使用这些示例运行的项目: https : //stackblitz.com/edit/typescript-observable-unsubscribe
Let me know if that helps!如果这有帮助,请告诉我!
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