Why does my app force close when I setText in an update method?

I have an android app I am just experimenting things on and I cannot seem to figure out why my app force closes when I update a TextView via a while loop. When I comment out the updateText method it runs fine.

    public class GameThread extends Thread {

 Thread t;
 private int i;
 private boolean running;
 private long sleepTime;
 GameView gv;

 public GameThread() {

  t = new Thread(this);
  t.start();
  i = 0;
  sleepTime = 1000;
 }

 public void initView(GameView v) {

  this.gv = v;
 }

 public void setRunning(boolean b) {

  this.running = b;
 }

 public boolean getRunning() {

  return running;
 }

 public void run() {

  while(running) {

   i++;
   update();

   try {

    t.sleep(sleepTime);
   } catch(InterruptedException e) {

   }
  }
 }

 public void update() {

  gv.setText(i); // when this is uncommented, it causes force close
  Log.v("Semajhan", "i = " + i);
 }


    public class GameView extends LinearLayout {

 public TextView tv;

 public GameView(Context c) {

  super(c);
  this.setBackgroundColor(Color.WHITE);
  tv = new TextView(c);
  tv.setTextColor(Color.BLACK);
  tv.setTextSize(20);
  this.addView(tv);
 }

 public void setText(int i) {

  tv.setText("i count: " + i);
 }


    public class Exp extends Activity {

 GameThread t;
 GameView v;
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        requestWindowFeature(Window.FEATURE_NO_TITLE);
        getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN, WindowManager开发者_如何学编程.LayoutParams.FLAG_FULLSCREEN);
        v = new GameView(this);
        setContentView(v);
        t = new GameThread();
        t.setRunning(true);
        t.initView(v);
    }

 public boolean onTouchEvent(MotionEvent event) {

  if (event.getAction() == MotionEvent.ACTION_DOWN) {

   if (t.getRunning() == true) {

    t.setRunning(false);
    Log.v("Semajhan", "STOPPED");
   } else {

    t.setRunning(true);
    Log.v("Semajhan", "RESTART");
   }
  }

  return true;
 }

    protected void onDestroy() {

     Log.v("Semajhan", "DESTROYING");
     super.onDestroy();
    }

    protected void onStop() {

     Log.v("Semajhan", "Stopping");
     super.onStop();
    }

I though i'd post the whole app since it is relatively small and so that I could get some help without confusion.

First, when you get a Force Close dialog, use adb logcat, DDMS, or the DDMS perspective in Eclipse to examine LogCat and look at the stack trace associated with your crash.

In this case, your exception will be something to the effect of "Cannot modify the user interface from a non-UI thread". You are attempting to call setText() from a background thread, which is not supported.

Using a GameThread makes sense if you are using 2D/3D graphics. It is not an appropriate pattern for widget-based applications. There are many, many, many, many examples that demonstrate how to create widget-based applications without the use of a GameThread.

You have to call it from the UI thread.

For more info check: Painless Threading .

If you decide to use a Handler, the easiest solution for you will be to:

1. Extend a View, override it's onDraw , in it draw the game objects, after you have calculated the game data for them first of course

2. The Handler: (in your Activity)

   private Handler playHandler = new Handler() {

   public void handleMessage(Message msg) {

       gameView.postInvalidate(); // gameView is the View that you extended
   

   }

   };

3. The game thread has a simple

Message.obtain(playHandler).sendToTarget();

In 2 words, the View is responsible for the drawing (you can move the calculations in a separate class, and call it before the onDraw), the thread is responsible only for scheduled calls to the Handler, and the Handler is responsible only to tell the View to redraw itself.

You cannot update the UI of your app outside of the UI Thread, which is the 'main' thread you start in. In onCreate(Context) of you app, you are creating the game thread object, which is what is doing the updating of your UI.

You should use a Handler:
http://developer.android.com/reference/android/os/Handler.html