拖动Button显示效果

public class DraftTest extends Activity {
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);

DisplayMetrics dm = getResources().getDisplayMetrics();
final int screenWidth = dm.widthPixels;
final int screenHeight = dm.heightPixels - 50;

final Button b=(Button)findViewById(R.id.btn);

b.setOnTouchListener(new OnTouchListener(){

int lastX, lastY;

@Override
public boolean onTouch(View v, MotionEvent event) {
// TODO Auto-generated method stub
int ea=event.getAction();
Log.i("TAG", "Touch:"+ea);

//Toast.makeText(DraftTest.this, "λ�ã�"+x+","+y, Toast.LENGTH_SHORT).show();

switch(ea){
case MotionEvent.ACTION_DOWN:
lastX = (int) event.getRawX();
lastY = (int) event.getRawY();
break;
/**
* layout(l,t,r,b)
* l  Left position, relative to parent
t  Top position, relative to parent
r  Right position, relative to parent
b  Bottom position, relative to parent
* */
case MotionEvent.ACTION_MOVE:
int dx =(int)event.getRawX() - lastX;
int dy =(int)event.getRawY() - lastY;

int left = v.getLeft() + dx;
int top = v.getTop() + dy;
int right = v.getRight() + dx;
int bottom = v.getBottom() + dy;

if(left < 0){
left = 0;
right = left + v.getWidth();
}

if(right > screenWidth){
right = screenWidth;
left = right - v.getWidth();
}

if(top < 0){
top = 0;
bottom = top + v.getHeight();
}

if(bottom > screenHeight){
bottom = screenHeight;
top = bottom - v.getHeight();
}

v.layout(left, top, right, bottom);

Log.i("", "position��" + left +", " + top + ", " + right + ", " + bottom);

lastX = (int) event.getRawX();
lastY = (int) event.getRawY();

break;
case MotionEvent.ACTION_UP:
break;
}
return false;
}});
}
}