Android任意拖动控件

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???"+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;			}});	}}