How to use AsyncTask

Android SDK - AsyncTask

import android.app.Activity;
import android.content.Context;
import android.os.AsyncTask;
import java.lang.ref.WeakReference;

private class MyTask extends AsyncTask<String, Integer, Long> {

    private WeakReference<Activity> mActivity;

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

    @Override
    protected void onPreExecute() {
        final Activity a = mActivity.get();
        if (a != null) {
            Context ctxt = a.getApplicationContext();
        }
    }

    @Override
    protected Long doInBackground(String... strings) {
        return 0;
    }

    @Override
    protected void onProgressUpdate(Integer... progress) {
    }

    @Override
    protected void onPostExecute(Long result) {
    }

    @Override
    protected void onCancelled() {
    }

}

final Activity a = mActivity.get();
if (a != null) {

Should be:

final Activity a = mActivity.get();
if (a == null)  return;