Pass Activity as WeakReference to avoid memory leaks

It is common for an AsyncTask to require a reference to the Activity that called it.

If the AsyncTask is an inner class of the Activity, then you can reference it and any member variables/methods directly.

If, however, the AsyncTask is not an inner class of the Activity, you will need to pass an Activity reference to the AsyncTask. When you do this, one potential problem that may occur is that the AsyncTask will keep the reference of the Activity until the AsyncTask has completed its work in its background thread. If the Activity is finished or killed before the AsyncTask’s background thread work is done, the AsyncTask will still have its reference to the Activity, and therefore it cannot be garbage collected.

As a result, this will cause a memory leak.

In order to prevent this from happening, make use of a WeakReference in the AsyncTask instead of having a direct reference to the Activity.

Here is an example AsyncTask that utilizes a WeakReference:

private class MyAsyncTask extends AsyncTask<String, Void, Void> {

    private WeakReference<Activity> mActivity;

    public MyAsyncTask(Activity activity) {
        mActivity = new WeakReference<Activity>(activity);
    }

    @Override
    protected void onPreExecute() {
        final Activity activity = mActivity.get();
        if (activity != null) {
            ....
        }
    }

    @Override
    protected Void doInBackground(String... params) {
        //Do something
        String param1 = params[0];
        String param2 = params[1];
        return null;
    }

    @Override
    protected void onPostExecute(Void result) {
        final Activity activity = mActivity.get();
        if (activity != null) {
            activity.updateUI();
        }
    }
}

Calling the AsyncTask from an Activity:

new MyAsyncTask(this).execute("param1", "param2");

Calling the AsyncTask from a Fragment:

new MyAsyncTask(getActivity()).execute("param1", "param2");