private int parentHeight;
private int parentWidth;

public DragFloatActionButton(Context context) {
    super(context);
}

public DragFloatActionButton(Context context, AttributeSet attrs) {
    super(context, attrs);

}

private int lastX;
private int lastY;

private boolean isDrag;
//& MotionEvent.ACTION_MASK
//最小滑动距离
private  int mTouchSlop;

@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
    super.onMeasure(widthMeasureSpec, heightMeasureSpec);
}
//主要代码：
@Override
public boolean onTouchEvent(MotionEvent event) {
    //初始化
    //记录 控件当前位置
    //获取系统的最小滑动距离
    int rawX = (int) event.getRawX();
    int rawY = (int) event.getRawY();
    if (mTouchSlop == 0) {
        final ViewConfiguration configuration = ViewConfiguration.get(getContext());
        mTouchSlop = configuration.getScaledTouchSlop();
    }
    switch (event.getAction() & MotionEvent.ACTION_MASK) {
        case MotionEvent.ACTION_DOWN:
            //按下操作时 设置按下 即非拖拽状态
            setPressed(true);
            isDrag=false;
            //告知父控件不做拦截处理，之后的一些操作即不拦截
            getParent().requestDisallowInterceptTouchEvent(true);
            //记录按下时坐标位置
            lastX=rawX;
            lastY=rawY;
            ViewGroup parent;
            if(getParent()!=null){
                parent= (ViewGroup) getParent();
                parentHeight=parent.getHeight();
                parentWidth=parent.getWidth();
            }
            break;
        case MotionEvent.ACTION_MOVE:
            //滑动状态下计算x,y相对位移
            int dx=rawX-lastX;
            int dy=rawY-lastY;
            //根据 移动距离 是否大于最小滑动距离   来判断是否在进行拖拽
            if (Math.sqrt(dx*dx+dy*dy)>mTouchSlop){
                isDrag=true;
            }else {
                isDrag=false;
                break;
            }
            //如果拖拽
            if (isDrag){
                float x=getX()+dx;
                float y=getY()+dy;
                //检测是否到达边缘 左上右下
                x=x<0?0:x>parentWidth-getWidth()?parentWidth-getWidth():x;
                y=getY()<0?0:getY()+getHeight()>parentHeight?parentHeight-getHeight():y;
                setX(x);
                setY(y);
                lastX=rawX;
                lastY=rawY;
            }

            break;
        case MotionEvent.ACTION_UP:
            //抬起时判断是否 拖拽过 来进行 动画 吸附到边上的效果
            if(!isNotDrag()){
                //恢复按压效果
                setPressed(false);
                //根据坐标 判断 靠左还是靠右吸附
                if(rawX>=parentWidth/2){
                    //靠右吸附
                    animate().setInterpolator(new DecelerateInterpolator())
                            .setDuration(500)
                            .xBy(parentWidth-getWidth()-getX())
                            .start();
                }else {
                    //靠左吸附
                    ObjectAnimator oa=ObjectAnimator.ofFloat(this,"x",getX(),0);
                    oa.setInterpolator(new DecelerateInterpolator());
                    oa.setDuration(500);
                    oa.start();
                }
            }
            break;
        case MotionEvent.ACTION_CANCEL:
            getParent().requestDisallowInterceptTouchEvent(false);
            setPressed(false);
            break;
    }
    //如果是拖拽则消s耗事件，否则正常传递即可。
    return !isNotDrag() || super.onTouchEvent(event);
}

private boolean isNotDrag(){
    return !isDrag&&(getX()==0
            ||(getX()==parentWidth-getWidth()));
}