我对“dispose”或“unsubscribe”函数的目的感到困惑,它(可选)从可观察的“executor”函数返回,如下所示:
const Rx = require('rxjs');
const obs = Rx.Observable.create(obs => {
// we are in the Observable "executor" function
obs.next(4);
// we return this function, which gets called if we unsubscribe
return function () {
console.log('disposed');
}
});
const s1 = obs.subscribe(
function (v) {
console.log(v);
},
function (e) {
console.log(e);
},
function () {
console.log('complete');
}
);
const s2 = obs.subscribe(
function (v) {
console.log(v);
},
function (e) {
console.log(e);
},
function () {
console.log('complete');
}
);
s1.unsubscribe();
s2.unsubscribe();
让我感到困惑的是,这样的函数实际上更有可能保留代码中的引用,从而防止垃圾回收。
谁能告诉我在那种情况下返回函数的目的是什么,函数被调用的是什么,它的签名是什么?我无法找出有关它的信息。
我还看到了从执行函数返回订阅的更复杂的示例,例如:
let index = 0;
let obsEnqueue = this.obsEnqueue = new Rx.Subject();
this.queueStream = Rx.Observable.create(obs => {
const push = Rx.Subscriber.create(v => {
if ((index % obsEnqueue.observers.length) === obsEnqueue.observers.indexOf(push)) {
obs.next(v);
}
});
return obsEnqueue.subscribe(push);
});
这似乎返回了一个订阅,而不仅仅是一个简单的函数。谁能解释一下这是怎么回事?
为了明确问题,这样做有什么区别:
const sub = new Rx.Subject();
const obs = Rx.Observable.create($obs => {
$obs.next(4);
return sub.subscribe($obs);
});
并且不返回订阅调用的结果:
const sub = new Rx.Subject();
const obs = Rx.Observable.create($obs => {
$obs.next(4);
sub.subscribe($obs);
});
最佳答案
Rx.Observable.create
需要返回的unsubscribe
函数在下游不再监听流时被调用,有效地让你有时间清理资源。
关于您的问题; .subscribe()
返回您可以调用 .unsubscribe()
的订阅。因此,如果您想对其他订阅执行某些操作,您可以将该订阅通过管道传输到您的下游:
const obs = Rx.Observable.create($obs => {
const timer = Rx.Observable.interval(300)
.do(i => console.log('emission: ' + i))
return timer.subscribe($obs);
});
obs.take(4).subscribe(i => console.log('outer-emission:'+i))
<script src="https://cdnjs.cloudflare.com/ajax/libs/rxjs/5.0.2/Rx.js"></script>
如果没有取消订阅功能,您将停止收听可观察对象,但内部创建的间隔将继续运行:
const obs = Rx.Observable.create($obs => {
const timer = Rx.Observable.interval(300)
.do(i => console.log('emission: ' + i))
.take(10)
.subscribe(
val => $obs.next(val),
err => $obs.error(err),
() => $obs.complete()
);
return function(){} // empty unsubscribe function, internal subscription will keep on running
});
obs.take(4).subscribe(i => console.log('outer-emission:'+i))
<script src="https://cdnjs.cloudflare.com/ajax/libs/rxjs/5.0.2/Rx.js"></script>
关于javascript - "Unsubscribe"函数回调/Observable 中的钩子(Hook) "executor"函数,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/41499889/