Handling long running tasks with RxJava

问题

I'm trying to migrate an AsyncTask that sends messages to the server, to use RxJava. Roughly, the task does the following:

1) Creates a message that will be sent (persists to the database)
2) Shows the message to the user (state 'sending')
3) Sends the message to the server (code snippet below)
4) Marks the message as sent or failed (persists to the database)
5) Updates the UI

I've created the required Rx chain which partially looks like this:

 public Observable<Message> sendMessage(Message message) {
     return mApiClient.sendMessage(message)
         .doOnNext(sentMessage -> mDatabase.synchroniseMessage(sentMessage))
         .doOnError(e -> {
             message.setState(FAILED);
             mDatabase.synchroniseMessage(message));
         })
         .onErrorReturn(e -> Observable.just(message));

When I subscribe to the above, I get a Disposable. Normally I'd add it to the CompositeDisposable object and clear that object then the user has moved to a different view (i.e. fragment). However, in this case, I need to keep running this task to make sure the local database is updated with the task results accordingly.

What would be the most appropriate way to handle this situation? I could simply not add the Disposable into my CompositeDisposable object and therefore it wouldn't be unsubscribed from, but it feels like it could cause issues.

P.S. Showing updates to the user is handled through observing the data in an SQLite table. These events are triggered by the synchroniseMessage method. This is a different subscription which I will simply unsubscribe from, so it's not part of the problem.

回答1:

One disposes of Disposable as soon as he is no longer interested in it.

In your case you are still interested in the stream regardless user navigates to another screen or no, which means you cannot unsubscribe from it. Which means you cannot add it to CompositeDisposable.

This will result in a situation, when your Activity cannot be garbage collected, because of a implicit reference to it from your Subscription, hence you are creating a memory leak situation.

If you have such a use case, I think you have to perform that request on a component, which will be activity lifecycle independent, like Service.

来源：https://stackoverflow.com/questions/43545272/handling-long-running-tasks-with-rxjava