Android实现悬浮可拖拽的Button

public class DraggingButton extends android.support.v7.widget.AppCompatButton {
 
  private int lastX = 0;
  private int lastY = 0;
  private int beginX = 0;
  private int beginY = 0;
 
  private int screenWidth = 720;
  private int screenHeight = 1280;
 
 
  public DraggingButton(Context context) {
    this(context, null);
  }
 
  public DraggingButton(Context context, @Nullable AttributeSet attrs) {
    this(context, attrs, 0);
  }
 
  public DraggingButton(Context context, @Nullable AttributeSet attrs, int defStyleAttr) {
    super(context, attrs, defStyleAttr);
 
    initData(context);
  }
 
  private void initData(Context context){
    WindowManager wm = (WindowManager) context.getSystemService(Context.WINDOW_SERVICE);
    DisplayMetrics dm = new DisplayMetrics();
    wm.getDefaultDisplay().getMetrics(dm);
    screenWidth = dm.widthPixels;
    screenHeight = dm.heightPixels;
  }
 
  @Override
  public boolean onTouchEvent(MotionEvent event)
  {
 
    switch (event.getAction())
    {
      case MotionEvent.ACTION_DOWN:
        lastX = (int) event.getRawX();   // 触摸点与屏幕左边的距离
        lastY = (int) event.getRawY();   // 触摸点与屏幕上边的距离
        beginX = lastX;
        beginY = lastY;
        break;
      case MotionEvent.ACTION_MOVE:
 
        int dx =(int)event.getRawX() - lastX;    // x轴拖动的绝对距离
        int dy =(int)event.getRawY() - lastY;    // y轴拖动的绝对距离
 
        // getLeft(): 子View的左边界到父View的左边界的距离, getRight():子View的右边界到父View的左边界的距离
        // 如下几个数据表示view应该在布局中的位置
        int left = getLeft() + dx;
        int top = getTop() + dy;
        int right = getRight() + dx;
        int bottom = getBottom() + dy;
        if(left <0){
          left = 0;
          right = left + getWidth();
        }
        if(right > screenWidth){
          right = screenWidth;
          left = right - getWidth();
        }
        if(top <0){
          top = 0;
          bottom = top + getHeight();
        }
        if(bottom>screenHeight){
          bottom = screenHeight;
          top = bottom - getHeight();
        }
        layout(left, top, right, bottom);
        lastX = (int) event.getRawX();
        lastY = (int) event.getRawY();
        break;
      case MotionEvent.ACTION_UP:
        // 解决拖拽的时候松手点击事件触发
        if (Math.abs(lastX - beginX) <10 && Math.abs(lastY - beginY) <10){
          return super.onTouchEvent(event);
        }else{
          setPressed(false);
          return true;
        }
      default:
        break;
    }
    return super.onTouchEvent(event);
  }
}

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private DraggingButton mDraggintView;
mDraggintView = (DraggingButton) findViewById(R.id.tv_dragging);
  mDraggintView.setOnClickListener(new View.OnClickListener() {
   @Override
   public void onClick(View v) {
    Toast.makeText(FloatingActionBtnTestActivity.this, "click", Toast.LENGTH_SHORT).show();
   }
  });