[英]Why my rxjs combineLatest output only 2 times?
請考慮以下rxjs@5.5.11代碼:
{ const source1 = Rx.Observable.of(1, 2, 3); const source2 = Rx.Observable.of(4, 5); const combined = Rx.Observable.combineLatest(source1, source2); const subscribe = combined.subscribe(([value1, value2]) => { console.log(`value1 Latest: ${value1}`); console.log(`value2 Latest: ${value2}`); }); }
<script src="https://cdnjs.cloudflare.com/ajax/libs/rxjs/5.5.11/Rx.min.js"></script>
我想象這個結果會是這樣的:
(發出1次並持續)
value1 Latest: 3
value2 Latest: 5
要么
(發出3次,並從每個持續)
value1 Latest: 1
value2 Latest: 4
value1 Latest: 2
value2 Latest: 5
value1 Latest: 3
value2 Latest: 5
但實際上它是:
(發出2次,並從每次持續)
value1 Latest: 3
value2 Latest: 4
value1 Latest: 3
value2 Latest: 5
為什么?
這些可觀察者都沒有任何延遲。 訂閱后, source1
將立即發出所有值1, 2, 3
。 然后它訂閱source2
,它發出的每個值都與source1
的最新值3
組合在一起。
在每個值之間添加微小延遲將強制每個事件按順序發出。 React甚至會尊重零延遲來強制執行此排序。 結果是它將交替地從每個事件中取一個事件:
{
const source1 = Rx.Observable.of(1, 2, 3)
.zip(Rx.Observable.timer(0, 0), (x, _) => x);
const source2 = Rx.Observable.of(4, 5)
.zip(Rx.Observable.timer(0, 0), (x, _) => x);
const combined = Rx.Observable.combineLatest(source1, source2);
const subscribe = combined.subscribe(([value1, value2]) => {
console.log(`value1 Latest: ${value1}`);
console.log(`value2 Latest: ${value2}`);
});
}
value1 Latest: 1
value2 Latest: 4
value1 Latest: 2
value2 Latest: 4
value1 Latest: 2
value2 Latest: 5
value1 Latest: 3
value2 Latest: 5
視覺解釋可能在這里很好。 原因可能是你的第一個和第二個observable發出如下內容:
First observable: -----1------2------3
Second observable: -----------------------4-----5
Result: ---------------------[3,4]--[3,5]
請注意, combineLatest
將等到兩個observable都發出值。
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