Android Asynctask: Is inner class necessary?

Question

I tried network connection in Android using Asynctask and succeeded better or not.

What I'm curious about: Is it necessary to make Asynctask inner class?

I didn't make it as a form of inner class, but Google API guide says AsyncTask must be subclassed to be used.(But I didn't and It works...) - http://developer.android.com/reference/android/os/AsyncTask.html

And why Asynctask takes a form of class even though it performs a only one main function? (I think it should be a method, not a class.)

Answer 1

'AsyncTask must be subclassed to be used' doesn't mean inner class; it means the class extends AsyncTask.

Generally people AVOID using ASyncTask as a (non-static) inner classes because there is a big and subtle problem which goes something like this:

1. You create the Asynctask as an inner class to your activity and it is off doing something time consuming. Inner classes by definition hold a reference to their 'outer' parent (this is how they access their parent's data).
2. Android shuts down the activity and restarts a new activity (for example when you rotate the phone).
3. Now the old activity and all it's resources are still being held because the Asynctask is still running and holding a reference to your old activity; so suddenly you are using memory for the old version of the activity AND the new version of the activity.

This difficulty is most easily solved by using a static inner class (which cannot reference it's outer parent) or a different class and only reference the activity using a weak_reference.

Answer 2

It doesn't have to be a inner class, it depends on what you are using it for.

for example, if you have a AsyncTask as inner class, only the class that holds it can use it, but you have a AsyncTask that a lot of classes are using, you may want to put the AsyncTask as a public class so everyone can use it.

it can work in both ways.

Answer 3

What I'm curious about: Is it necessary to make Asynctask inner class?

No, you can put it to external java file, or you can also make it inner static class.

AsyncTask must be subclassed to be used.

it has nothing to do with class being inner, it says you need to make a subclass of AsyncTask ie:

class MyAsyncTask extends AsyncTask 

inner class looks like that:

class MyActivity extends Activity {
    // now MyAsyncTask  is inner to MyActivity and has full access to its instance
    class MyAsyncTask extends AsyncTask
    {}
} 

And why Asynctask takes a form of class even though it performs a only one main function? (I think it should be a method, not a class.)

it perform a lot more, like onPostExecute, onPreExecute, look at it closer. Also it decouples AsyncTask logic and allows for reuse.

If you want AsyncTask to be inner, then I suggest to make it static - but then why not make it external class. Inner class always keep reference to its external class, this way in this case Activity will not be garbage collected untill AsyncTask finishes its job (thread ends), because network communication takes time this might cause problems - like leaked references, or OOM (Out Of Memory) exceptions if your activity uses lots of memory. Its better to keep reference to your Activity in WeakReference to allow Activity to be garbace collected.