What is the lifecycle of Loaders?

Question

Background

I'm working on making an app better by supporting its landscape mode. One thing that I use a lot is Loaders, or more specifically AsyncTaskLoaders .

Using Loaders allow you to keep doing a background task even if the activity is being re-created due to orientation changes, as opposed to AsyncTask.

The question

I'd like to ask about the lifecycle of Loaders:

1. When do they get GC-ed ? Do I have to keep track of them, and if one has a bitmap inside, should I abandon it as soon as possible? Do they perhaps get GC-ed only after the activity is really destroyed (and not because of configuration changes) ?
2. I've noticed they have states of being stopped. Does this somehow allow me to pause them?
3. If #2 is true, How would I implement a loader that can be paused on some points of itself?
4. Can fragments also have Loaders? As I've noticed, it's only for activities.
5. if #4 is false, what is the recommended way to use loaders in the design pattern of navigation-drawer that replaces fragments in the container?
6. Can AsyncTaskLoader be interrupted like AsyncTask (or threads)? I've looked at its code and at the API, but I can't find it. I've also tried to find a workaround, but I didn't succeed.
7. If #6 is false, is there an alternative? For example, if I know that the loader doesn't need to load something, I could just stop it right away. One way I can think of is to set a flag (maybe AtomicBoolean, just in case) that will tell it to stop, and check this value sometimes within. Problem is that I will need to add it even inside functions that it uses, while an easier way would be to call "Thread.sleep(0)" or something like that.
8. Is there somewhere an explanation of the lifecycle of Loaders?
9. Do AsyncTaskLoaders work together, at the same time, or are they like the default, current behavior of AsyncTask, which runs only on a single thread ?

Answer 1

1.When do they get GC-ed ? Do I have to keep track of them, and if one has a bitmap inside, should I abandon it as soon as possible? Do they perhaps get GC-ed only after the activity is really destroyed (and not because of configuration changes) ?

Since the loader lifecycle is tied to the activity/fragment lifecycle, it is safe to assume that the garbage collection pretty much takes place at the same time. Take a look at #8 for the lifecycle of loaders. Might give you some ideas.

2.I've noticed they have states of being stopped. Does this somehow allow me to pause them?

No, as far as i know loaders do not have a onPause() per say.

3.If #2 is true, How would I implement a loader that can be paused on some points of itself?

I really have no answer to this one. Would like to know a solution to this myself.

4.Can fragments also have Loaders? As I've noticed, it's only for activities.

Of course fragments can have loaders. Just initialize the loaderManager in the onActivityCreated() method

5.if #4 is false, what is the recommended way to use loaders in the design pattern of navigation-drawer that replaces fragments in the container?

4 is true. So this question is irrelevant i guess.

6.Can AsyncTaskLoader be interrupted like AsyncTask (or threads)? I've looked at its code and at the API, but I can't find it. I've also tried to find a workaround, but I didn't succeed.

I am not sure what do you mean interrupting the loaders. But if you mean having something similar to a isCancelled() method, then there is a method called cancelLoad() on the AsyncTaskLoader. The complete flow is like cancelLoad()->cancel()->onCancelled() i think.

7.If #6 is false, is there an alternative? For example, if I know that the loader doesn't need to load something, I could just stop it right away. One way I can think of is to set a flag (maybe AtomicBoolean, just in case) that will tell it to stop, and check this value sometimes within. Problem is that I will need to add it even inside functions that it uses, while an easier way would be to call "Thread.sleep(0)" or something like that.

Irrelevant again?

9.Do AsyncTaskLoaders work together, at the same time, or are they like the default, current behavior of AsyncTask, which runs only on a single thread ?

Runs on a single thread.

8.Is there somewhere an explanation of the lifecycle of Loaders?

To my best of knowledge:

• When activity/fragment is created the loader starts -> onStartLoading()

• When activity becomes invisible or the fragment is detached the loader stops -> onStopLoading()

• No callback when either the activity or the fragment is recreated. The LoaderManager stores the results in a local cache.

• When activity/fragment is destroyed -> restartLoader() or destroyLoader() is called and the loader resets.

I hope this helps. I might be a bit off on some of the answers. I am constantly learning new things myself. Cheers.