white screen when using runOnUiThread

Question

I am having an experiment of onTouchListener. The aim is to move the FrameLayout to wherever I touch. The 1st version of code gives me a “viewroot$calledfromwrongthreadexception” error. So in the 2nd version, I try to use runOnUiThread to solve the error. But doing so, only gives a white screen.

public class MainActivity extends Activity implements Runnable, OnTouchListener{

private int x,y;
private boolean p_running = false;
private FrameLayout mFrame;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_main);

    mFrame=(FrameLayout) findViewById(R.id.frameLayout1);
    mFrame.setOnTouchListener(this);
    p_running = true;

    runOnUiThread(new Thread(new Runnable(){
            @Override
            public void run(){
                while (p_running){
                mFrame.setPadding(x,y,0,0);
                }
            }
            }));

}

@Override 
public boolean onTouch(View v, MotionEvent event){

    x = (int)event.getX();
    y = (int)event.getY();

    return true;
} 

 @Override
 public void run() {
// TODO Auto-generated method stub

 }

 }

Answer 1

The onCreate method runs on the main (UI) thread and your posting a Runnable to run on the main (UI) thread.

In that thread you have a loop with

while (p_running)

so this while loop is running on the UI thread in an infinite loop.

You could simply move that code to another Thread like so

Thread t = new Thread (){

    @Override
    public void run(){
        while (p_running){
            runOnUiThread(new Runnable(){

                @Override
                public void run(){
                    mFrame.setPadding(x,y,0,0);
                }

             });
        }
    }
});
t.start();

but there are still issues with that as you are constantly posting new Runnables to the UI thread which will probably result in very poor UI response