android學習之拖動Button顯示效果

編輯：開發入門

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);


      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 l=v.getLeft()+dx;
         int b=v.getBottom()+dy;
         int r=v.getRight()+dx;
         int t=v.getTop()+dy;
         if(l<0){
         l=0;
         r=l+v.getWidth();
         }

         if(t<0){
         t=0;
         b=t+v.getHeight();
         }

         if(r>screenWidth){
         r=screenWidth;
         l=r-v.getWidth();
         }

         if(b>screenHeight){
         b=screenHeight;
         t=b-v.getHeight();
         }
         v.layout(l, t, r, b);

         lastX=(int)event.getRawX();
         lastY=(int)event.getRawY();
         Toast.makeText(DraftTest.this,
         "當前位置："+l+","+t+","+r+","+b,
         Toast.LENGTH_SHORT).show();
         v.postInvalidate();
         break;
      case MotionEvent.ACTION_UP:
         break;
      }
return false;
}});
}
}
運行效果如下：
QQ截圖未命名.jpg

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