RxJava – How to stop (and resume) a Hot Observable (interval)?

RxJava – How to Stop (and Resume) a Hot Observable (interval)?

Understanding Hot Observables

In RxJava, a “hot” observable emits items regardless of whether there are subscribers or not. This contrasts with “cold” observables, which only begin emitting items when a subscriber attaches. The `interval()` operator in RxJava creates a hot observable that emits items at regular intervals.

Stopping the Interval

There are a few ways to stop the interval emitted by a hot observable. Here are the most common methods:

1. Using `take(count)` Operator

The `take(count)` operator allows you to limit the number of items emitted by an observable. Once the specified number of items is emitted, the observable completes.

“`java
Observable observable = Observable.interval(1, TimeUnit.SECONDS)
.take(5); // Emits 5 items then completes

observable.subscribe(item -> System.out.println(“Item: ” + item));
“`

“`
Item: 0
Item: 1
Item: 2
Item: 3
Item: 4
“`

2. Using `takeUntil(trigger)` Operator

The `takeUntil(trigger)` operator allows you to stop the interval based on another observable (the trigger). The interval will emit items until the trigger observable emits an item, then it completes.

“`java
Observable observable = Observable.interval(1, TimeUnit.SECONDS)
.takeUntil(Observable.timer(5, TimeUnit.SECONDS)); // Stops after 5 seconds

observable.subscribe(item -> System.out.println(“Item: ” + item));
“`

“`
Item: 0
Item: 1
Item: 2
Item: 3
Item: 4
“`

3. Using `dispose()` on Subscription

When you subscribe to an observable, you receive a `Subscription` object. You can call the `dispose()` method on this object to immediately stop the observable’s emissions.

“`java
Subscription subscription = Observable.interval(1, TimeUnit.SECONDS)
.subscribe(item -> System.out.println(“Item: ” + item));

// Stop after 5 seconds
Thread.sleep(5000);
subscription.dispose();
“`

“`
Item: 0
Item: 1
Item: 2
Item: 3
Item: 4
“`

Resuming the Interval

Resuming a stopped hot observable is not directly possible. Once a hot observable completes or is disposed, it cannot be restarted in the same way.

Alternative Solution: Recreate the Observable

If you need to resume the interval, the recommended approach is to recreate the observable using the `interval()` operator again. This will create a fresh observable that can be subscribed to and will begin emitting items at the specified interval.

“`java
// Assuming you have a flag to track whether the observable is active
boolean observableActive = false;
Observable observable = null;

// Start the observable
if (!observableActive) {
observable = Observable.interval(1, TimeUnit.SECONDS)
.subscribe(item -> System.out.println(“Item: ” + item));
observableActive = true;
}

// Stop the observable (e.g., by setting a flag)
if (observableActive) {
observable.dispose();
observableActive = false;
}

// Resume the observable
if (!observableActive) {
observable = Observable.interval(1, TimeUnit.SECONDS)
.subscribe(item -> System.out.println(“Item: ” + item));
observableActive = true;
}
“`

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