Question

我知道RxJS 5（以及其他地方）的可观察者是懒惰的。换句话说，在有订户之前，它们不会被执行。但是，我试图预取一些数据。有没有办法在订阅它之前触发observable？

let obs = Rx.Observable.create(observer => {
  console.log('Observer executed');
  // This would actually be fetching data from a server:
  observer.next(42);
});

// Something like obs.warmup() happens here
console.log('Observer is ideally called before this point.');

// Some time later this is called, and hopefully the data is already retrieved.
obs.subscribe(value => {
  console.log('Got ' + value);
});

Answer 1

你想做一个冷的可观察热。（what are hot and cold observables）

因此，如果您已经有冷观察，则可以使用publish运算符和connect。

＆＃13;

let obs = Rx.Observable.create(observer => {
  console.log('Observer executed');
  // This would actually be fetching data from a server:
  observer.next(42);
}).publish(); // create a ConnectableObservable

obs.connect(); // Run the observer

// Something like obs.warmup() happens here
console.log('Observer is ideally called before this point.');

// Some time later this is called, and hopefully the data is already retrieved.
obs.subscribe(value => {
  console.log('Got ' + value);
});

＆＃13;

<script src="https://cdnjs.cloudflare.com/ajax/libs/rxjs/5.0.0-rc.1/Rx.js"></script>

＆＃13;

但通常有一种更简单的方法。我假设您有一个外部事件源，您希望将其转换为可观察事件。正确的方法是使用Subject。

＆＃13;

let obs = new Rx.Subject();

console.log('Observer executed');
obs.next(42); // subscribers would receive this... 
// it could be something like `service.on("event", e => obs.next(e));`

// Something like obs.warmup() happens here
console.log('Observer is ideally called before this point.');

// Some time later this is called, and hopefully the data is already retrieved.
obs.subscribe(value => {
  console.log('Got ' + value);
});

＆＃13;

<script src="https://cdnjs.cloudflare.com/ajax/libs/rxjs/5.0.0-rc.1/Rx.js"></script>

＆＃13;

在RxJS 5中，有没有办法在订阅Observable之前触发它？

1 个答案: