如何确保我的后台线程绑定到我的 ViewModel 而不是 Zombie Activity？ (安卓/Java/MVVM)

Question

I recently implemented a ViewModel and some LiveData components to hold a list of results fetched from a webpage on my Android App in Java.

My goal is to ensure that on configuration changes (changing from portrait to landscape for example) that any background threads fetching data are not tied to dead/Zombie activities and tied to the ViewModel itself so that there aren't duplicated threads causing memory leaks.

My question is: is starting a thread from within a ViewModel enough to ensure the thread is tied to the ViewModel and not possibly a zombie Activity? I understand the ViewModel is lifecycle aware, so it does not "die" or get destroyed upon configuration changes.

I have my Application class hold a global ExecutorService and Handler:

public class MyApplication extends Application {

    private ExecutorService executorService = Executors.newSingleThreadExecutor();
    private Handler mainThreadHandler = Handler.createAsync(Looper.getMainLooper());

    public Handler getMainThreadHandler() {
        return mainThreadHandler;
    }

    public ExecutorService getExecutorService() {
        return executorService;
    }

When the user clicks a button to start the fetching of data on the Activity's View, the Activity calls the search function of the ViewModel and passes in the handler and executor service:

public class MyViewModel extends ViewModel {

    ...

    public void SearchForResults(final String state, final String name, final ExecutorService  executorService, final Handler handler)
    {

        executorService.submit(new Runnable() {
            @Override
            public void run() {
                /*NETWORK LOGIC - FILTERING,ETC*/

                ...

                /* to update LiveData class variables of ViewModel */
                handler.post(new Runnable() {  
                    @Override
                    public void run() {
                        liveData1.setValue(true);
                        liveData2.setValue(false);
                    }
                });

            }
        });
    }

Will these threads be held to the ViewModel in case the Activity is destroyed while they are still running in the background? How can we determine what the "owner" of the threads are?

Is it proper to use a UI thread handler to update class variables of the ViewModel from the background thread?

Thanks for your help.

Answer 1

My question is: is starting a thread from within a ViewModel enough to ensure the thread is tied to the ViewModel and not possibly a zombie Activity?

Yes, though you still have to be careful of any references your thread is holding on to. If it is holding on to an Activity or View or something else that itself is holding on to the Activity that you might have passed to the ViewModel, then you have a problem.

Will these threads be held to the ViewModel in case the Activity is destroyed while they are still running in the background?

Yes.

How can we determine what the "owner" of the threads are?

Well, the "owner" is the thing that started the thread so you should know who the owner is. You shouldn't have to gleam that from the thread itself.

Is it proper to use a UI thread handler to update class variables of the ViewModel from the background thread?

I don't know about "proper" - Kotlin and coroutines are the rage these days - but since you're using Java, it's probably fine.