android 实现可拖动的Button
实现效果，Buttton在屏幕范围内到处拖动，但不会拖出屏幕，代码如下：
public class DraftTest extends Activity { @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();//获取触摸事件触摸位置的原始X坐标 lastY=(int)event.getRawY(); break; 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; //下面判断移动是否超出屏幕 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, "当前位置："+l+","+t+","+r+","+b, Toast.LENGTH_SHORT).show(); v.postInvalidate(); break; case MotionEvent.ACTION_UP: break; } return false; }}); }}
