Android :: How To Update View Object On Main Thread By Background?

My purpose is very simple : each 1second, I want to redraw an object on different place on background. I do not know where my error on this code below. Here is my code:
public class My_View extends View{ private Bitmap mBackground_img;
private Drawable mMoveObject; private int mObjectw,mObjecth; private int Dx,Dy;
private Handler myHandler = new Handler(); private long lasttime;
public My_View(Context context,AttributeSet ats,int ds) {
super(context,ats,ds); init(context);
} public My_View(Context context,AttributeSet ats) { super(context,ats);
init(context); } public My_View(Context context) { super(context);
init(context); } public void change() { invalidate();
} private void init(Context context) {
Resources res = context.getResources();
mMoveObject = res.getDrawable (R.drawable.lander_firing);
mBackground_img = BitmapFactory.decodeResource(res, R.drawable.my_pic);
mObjectw = mMoveObject.getIntrinsicWidth();
mObjecth = mMoveObject.getIntrinsicHeight();
Dx = Dy = 0; lasttime = System.currentTimeMillis() + 1000;
Thread mthread = new Thread(null,doBackground,"Background");
mthread.start(); } private Runnable doBackground = new Runnable() {
public void run() { long now = System.currentTimeMillis();
if(lasttime < now ) { Dx = Dx + 10; Dy = Dy + 10;
lasttime = now + 1000; myHandler.post(change_view);
} } }; private Runnable change_view = new Runnable() {
public void run() { change();
} };
@Override public void onDraw(Canvas canvas) {
canvas.drawBitmap(mBackground_img,0 ,0 , null);
mMoveObject.setBounds(Dx, Dy, Dx+mObjectw, Dy+mObjecth);
mMoveObject.draw(canvas);
} }