Sometimes it is necessary to do a cleanup on the internal resources that were used to feed Emitter when an Observable completes. Consider this example where we will click events from a View:

Observable.create(emitter -> {
    helloText.setOnClickListener(v -> emitter.onNext(v));
});

This Observable never completes but even if it terminates, there is still a problem present--the reference to the Emitter (and thus Observable) will alway be present because the following call created a ClickListener that never went away:

helloText.setOnClickListener(v -> emitter.onNext(v));

So, the ClickListener always has a reference to the Emitter, and Emitter has a reference to the Observable. The memory will never be freed up, and the setOnClickListener() listener will keep calling:

v -> emitter.onNext(v)

To fix this, we need to add a Cancellable action with this:

emitter.setCancellable(() -> helloText.setOnClickListener(null));

This way, the listener on TextView will be cleaned up. This method can be used to clean up other kinds of resources, such as these:

• Closing files
• Closing remote socket connections
• Terminating threads
• Others

So, now the block with clean up code can look as follows:

Observable.create(emitter -> {
    emitter.setCancellable(() -> helloText.setOnClickListener(null));
    helloText.setOnClickListener(v -> emitter.onNext(v));
})

In this particular case, since we are working with Views, it is advised to use MainThreadDisposable from the RxAndroid library. Consider the following example:

Observable.create(emitter -> {
    emitter.setDisposable(new MainThreadDisposable() {
        @Override
        protected void onDispose() {
            helloText.setOnClickListener(null);
        }
    });
    helloText.setOnClickListener(v -> emitter.onNext(v));
})

This way, the interaction with the TextView will happen on the main Android UI thread. Also, in this case, we've used the .setDisposable() method; it serves the same purpose as .setCancellable() but is used in cases where the Disposable interface is already available from somewhere else.