Question

How can i send a message between an activity and a thread if put the thread in a class?

Okay, here is a little more detailed code:

public class AnActivity extends Activity implements OnClickListener, Callback
{

    Button          b           = null;
    TextView        t           = null;
    MyThread        mThread     = null;
    public Handler  mainHandler = new Handler( this );

    @Override
    public void onCreate( Bundle savedInstanceState )
    {
        super.onCreate( savedInstanceState );
        setContentView( R.layout.main );

        b = ( Button ) findViewById( R.id.buttonSEND );

        b.setOnClickListener( this );
        mThread = new MyThread( this );
        mThread.start();
    }

    @Override
    public void onClick( View v )
    {
        Message m = Message.obtain();
        m.what = 4;
        mThread.myThreadHandler.sendMessage( m );
    }

    @Override
    public boolean handleMessage( Message msg )
    {
        Toast.makeText( this, "What= " + Integer.toString( msg.what ), Toast.LENGTH_SHORT ).show();
        return false;
    }
}

The following class is not a part of AnActivity

public class MyThread extends Thread
{
    public Handler myThreadHandler;
    Activity mainActivity;

    public MyThread ( AnActivity anActivity )
    {
        this.mainActivity = anActivity;     
    }


    @Override
    public void run()
    {
        Looper.prepare();
        myThreadHandler = new Handler()
        {
            // sending back a message immediately after a received one
            public void handleMessage( Message msg )
            {
                Message m = Message.obtain();
                m.what = 10;
                // MY PROBLEM:
                // mainActivity.mainHandler.sendMessage( m ); // mainHandler is not visible
                // mainActivity.sendMessage( m ); // does not working
            }
        };
        Looper.loop();
    }
}

Answer 1

This is my Activity:

public class AnActivity extends Activity implements OnClickListener, Callback
{

    Button          b           = null;
    TextView        t           = null;
    MyThread        mThread     = null;
    public Handler  mainHandler = new Handler( this );


    @Override
    public void onCreate( Bundle savedInstanceState )
    {
        super.onCreate( savedInstanceState );
        setContentView( R.layout.main );

        b = ( Button ) findViewById( R.id.buttonSEND );

        b.setOnClickListener( this );
        mThread = new MyThread( this );
        mThread.start();
    }


    @Override
    public void onClick( View v )
    {
        Message m = Message.obtain();
        m.what = 4;
        mThread.myThreadHandler.sendMessage( m );
    }


    @Override
    public boolean handleMessage( Message msg )
    {
        Toast.makeText( this, "This is AnActivity. What=" + Integer.toString( msg.what ), Toast.LENGTH_SHORT ).show();
        return false;
    }
}

Modified thread:
In the constructor i can store UI thread’s messagehandler.

public class MyThread extends Thread
{
    public Handler  myThreadHandler;
    Activity        mainActivity;
    Handler         mainHandler;
    int             what    = -1;


    public MyThread ( AnActivity anActivity )
    {
        this.mainActivity = anActivity;
        this.mainHandler = anActivity.mainHandler;
    }


    @Override
    public void run()
    {
        Looper.prepare();
        myThreadHandler = new Handler()
        {
            public void handleMessage( Message msg )
            {
                what = msg.what;


                // Writing back to main UI thread
                mainActivity.runOnUiThread( new Runnable()
                {

                    @Override
                    public void run()
                    {
                        Toast.makeText( mainActivity, "This is MyThread. What=" + Integer.toString( what ), Toast.LENGTH_SHORT ).show();

                    }
                } );

                Message m = Message.obtain();
                m.what = 10;
                mainHandler.obtainMessage( 12 ).sendToTarget();
            }
        };
        Looper.loop();
    }
}