public class AsyncTaskTrapActivity extends Activity {
    private SimpleAsyncTask asynctask;
    private Looper myLooper;
    private TextView status;

    @Override
    public void onCreate(Bundle icicle) {
        super.onCreate(icicle);
        asynctask = null;
        new Thread(new Runnable() {
            @Override
            public void run() {
                Looper.prepare();
                myLooper = Looper.myLooper();
                status = new TextView(getApplication());
                asynctask = new SimpleAsyncTask(status);
                Looper.loop();
            }
        }).start();
        try {
            Thread.sleep(1000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        LayoutParams params = new LayoutParams(LayoutParams.FILL_PARENT, LayoutParams.FILL_PARENT);
        setContentView((TextView) status, params);
        asynctask.execute();
    }

    @Override
    public void onDestroy() {
        super.onDestroy();
        myLooper.quit();
    }

    private class SimpleAsyncTask extends AsyncTask<Void, Integer, Void> {
        private TextView mStatusPanel;

        public SimpleAsyncTask(TextView text) {
            mStatusPanel = text;
        }

        @Override
        protected Void doInBackground(Void... params) {
            int prog = 1;
            while (prog < 101) {
                SystemClock.sleep(1000);
                publishProgress(prog);
                prog++;
            }
            return null;
        }

        // Not Okay, will crash, said it cannot touch TextView
        @Override
        protected void onPostExecute(Void result) {
            mStatusPanel.setText("Welcome back.");
        }

        // Okay, because it is called in #execute() which is called in Main thread, so it runs in Main Thread.
        @Override
        protected void onPreExecute() {
            mStatusPanel.setText("Before we go, let me tell you something buried in my heart for years...");
        }

        // Not okay, will crash, said it cannot touch TextView
        @Override
        protected void onProgressUpdate(Integer... values) {
            mStatusPanel.setText("On our way..." + values[0].toString());
        }
    }
}

11-03 09:13:10.501: E/AndroidRuntime(762): FATAL EXCEPTION: Thread-10
11-03 09:13:10.501: E/AndroidRuntime(762): android.view.ViewRoot$CalledFromWrongThreadException: Only the original thread that created a view hierarchy can touch its views.
11-03 09:13:10.501: E/AndroidRuntime(762):  at android.view.ViewRoot.checkThread(ViewRoot.java:2990)
11-03 09:13:10.501: E/AndroidRuntime(762):  at android.view.ViewRoot.requestLayout(ViewRoot.java:670)
11-03 09:13:10.501: E/AndroidRuntime(762):  at android.view.View.requestLayout(View.java:8316)
11-03 09:13:10.501: E/AndroidRuntime(762):  at android.view.View.requestLayout(View.java:8316)
11-03 09:13:10.501: E/AndroidRuntime(762):  at android.view.View.requestLayout(View.java:8316)
11-03 09:13:10.501: E/AndroidRuntime(762):  at android.view.View.requestLayout(View.java:8316)
11-03 09:13:10.501: E/AndroidRuntime(762):  at android.widget.TextView.checkForRelayout(TextView.java:6477)
11-03 09:13:10.501: E/AndroidRuntime(762):  at android.widget.TextView.setText(TextView.java:3220)
11-03 09:13:10.501: E/AndroidRuntime(762):  at android.widget.TextView.setText(TextView.java:3085)
11-03 09:13:10.501: E/AndroidRuntime(762):  at android.widget.TextView.setText(TextView.java:3060)
11-03 09:13:10.501: E/AndroidRuntime(762):  at com.hilton.effectiveandroid.os.AsyncTaskTrapActivity$SimpleAsyncTask.onProgressUpdate(AsyncTaskTrapActivity.java:110)
11-03 09:13:10.501: E/AndroidRuntime(762):  at com.hilton.effectiveandroid.os.AsyncTaskTrapActivity$SimpleAsyncTask.onProgressUpdate(AsyncTaskTrapActivity.java:1)
11-03 09:13:10.501: E/AndroidRuntime(762):  at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:466)
11-03 09:13:10.501: E/AndroidRuntime(762):  at android.os.Handler.dispatchMessage(Handler.java:130)
11-03 09:13:10.501: E/AndroidRuntime(762):  at android.os.Looper.loop(Looper.java:351)
11-03 09:13:10.501: E/AndroidRuntime(762):  at com.hilton.effectiveandroid.os.AsyncTaskTrapActivity$1.run(AsyncTaskTrapActivity.java:56)
11-03 09:13:10.501: E/AndroidRuntime(762):  at java.lang.Thread.run(Thread.java:1050)
11-03 09:13:32.823: E/dalvikvm(762): [DVM] mmap return base = 4585e000

new InternalHandler() {

     if (Looper.myLooper() != Looper.getMainLooper()) {
  throw new RuntimeException("AsyncTask must be initialized in main thread");
     }

11-03 08:56:07.055: E/AndroidRuntime(890): FATAL EXCEPTION: Thread-10
11-03 08:56:07.055: E/AndroidRuntime(890): java.lang.ExceptionInInitializerError
11-03 08:56:07.055: E/AndroidRuntime(890):  at com.hilton.effectiveandroid.os.AsyncTaskTrapActivity$1.run(AsyncTaskTrapActivity.java:55)
11-03 08:56:07.055: E/AndroidRuntime(890):  at java.lang.Thread.run(Thread.java:1050)
11-03 08:56:07.055: E/AndroidRuntime(890): Caused by: java.lang.RuntimeException: AsyncTask must be initialized in main thread
11-03 08:56:07.055: E/AndroidRuntime(890):  at android.os.AsyncTask$InternalHandler.<init>(AsyncTask.java:455)
11-03 08:56:07.055: E/AndroidRuntime(890):  at android.os.AsyncTask.<clinit>(AsyncTask.java:183)
11-03 08:56:07.055: E/AndroidRuntime(890):  ... 2 more

 new IntentHandler() {
     super(Looper.getMainLooper());
 }

 if (Looper.myLooper() != Looper.getMainLooper()) {
    throw new RuntimeException("This method can only be called in main thread");
 }

loop() {
   while (true) {
      Message msg = mQueue.next();
      if msg is a quit message, then
         return;
      msg.processMessage(msg)
   }
}

public void prepareMainLooper() {
    if (getMainLooper() != null) {
         throw new RuntimeException("Looper.prepareMainthread() can ONLY be called by Frameworks");
     }
     //...
}