iOS-悬浮物（仿微信视频对话框，可拖动，加重力动画）

首先添加拖动手势

UIPanGestureRecognizer *pan=[[UIPanGestureRecognizer alloc]initWithTarget:self action:@selector(handlePan:)];
    [mineView setUserInteractionEnabled:YES];//开启图片控件的用户交互
    [mineView addGestureRecognizer:pan];//给图片添加手势

在拖拽方法里面执行：

    CGFloat KWidth = [UIScreen mainScreen].bounds.size.width;
    CGFloat KHeight = [UIScreen mainScreen].bounds.size.height;
    //返回在横坐标上、纵坐标上拖动了多少像素
    CGPoint point=[rec translationInView:self];
    NSLog(@"%f,%f",point.x,point.y);
    
    CGFloat centerX = rec.view.center.x+point.x;
    
    CGFloat centerY = rec.view.center.y+point.y;

    CGFloat viewHalfH = rec.view.frame.size.height/2;
    CGFloat viewhalfW = rec.view.frame.size.width/2;
    
    //确定特殊的centerY
    if (centerY - viewHalfH < 0 ) {
        centerY = viewHalfH;
    }
    if (centerY + viewHalfH > KHeight ) {
        centerY = KHeight - viewHalfH;
    }

    //确定特殊的centerX
    if (centerX - viewhalfW < 0){
        centerX = viewhalfW;
    }
    if (centerX + viewhalfW > KWidth){
        centerX = KWidth - viewhalfW;
    }
    rec.view.center = CGPointMake(centerX, centerY);
    //拖动完之后，每次都要用setTranslation:方法制0这样才不至于不受控制般滑动出视图
    [rec setTranslation:CGPointMake(0, 0) inView:self];

可实现在屏幕内部拖拽且不脱离屏幕外部。

下面实现类似微信两人视频对话时，对话框拖拽的效果（增加重力动画）：

- (void)handlePan:(UIPanGestureRecognizer *)rec {
    CGFloat KWidth = [UIScreen mainScreen].bounds.size.width;
    CGFloat KHeight = [UIScreen mainScreen].bounds.size.height;
    //返回在横坐标上、纵坐标上拖动了多少像素
    CGPoint point=[rec translationInView:self];
    NSLog(@"%f,%f",point.x,point.y);
    
    CGFloat endX = rec.view.center.x+point.x;
    
    CGFloat endY = rec.view.center.y+point.y;

    CGFloat viewHalfH = rec.view.frame.size.height/2;
    CGFloat viewhalfW = rec.view.frame.size.width/2;
    

    if (rec.state == UIGestureRecognizerStateEnded) {
        //计算距离最近的边缘 吸附到边缘停靠

        CGFloat topRange = endY;//上距离
        
        CGFloat bottomRange = KHeight - endY;//下距离
        
        CGFloat leftRange = endX;//左距离
        
        CGFloat rightRange = KWidth - endX;//右距离
        
        
        //比较上下左右距离 取出最小值
        
        CGFloat minRangeTB = topRange > bottomRange ? bottomRange : topRange;//获取上下最小距离
        
        CGFloat minRangeLR = leftRange > rightRange ? rightRange : leftRange;//获取左右最小距离
        
        CGFloat minRange = minRangeTB > minRangeLR ? minRangeLR : minRangeTB;//获取最小距离
        
        
        //判断最小距离属于上下左右哪个方向 并设置该方向边缘的point属性
        
        CGPoint minPoint;
        
        if (minRange == topRange) {
            
            //上
            
            endX = endX - viewhalfW < 0 ? viewhalfW : endX;
            
            endX = endX + viewhalfW > KWidth ? KWidth - viewhalfW : endX;
            
            minPoint = CGPointMake(endX , 0 + viewHalfH);
            
        } else if(minRange == bottomRange){
            
            //下
            
            endX = endX - viewhalfW < 0 ? viewhalfW : endX;
            
            endX = endX + viewhalfW > KWidth ? KWidth - viewhalfW : endX;
            
            minPoint = CGPointMake(endX , KHeight - viewHalfH);
            
        } else if(minRange == leftRange){
            
            
            
            //左
            
            endY = endY - viewHalfH < 0 ? viewHalfH : endY;
            
            endY = endY + viewHalfH > KHeight ? KHeight - viewHalfH : endY;
            
            minPoint = CGPointMake(0 + viewhalfW , endY);
            
        } else {
            
            //右
            
            endY = endY - viewHalfH < 0 ? viewHalfH : endY;
            
            endY = endY + viewHalfH > KHeight ? KHeight - viewHalfH : endY;
            
            minPoint = CGPointMake(KWidth - viewhalfW , endY);
            
        }
        
        // 不加动画的话，显示下面这个
        //            rec.view.center = minPoint;
        
        //添加吸附物理行为
        UIAttachmentBehavior *attachmentBehavior = [[UIAttachmentBehavior alloc] initWithItem:self.mineView attachedToAnchor:minPoint];
        [attachmentBehavior setLength:0];
        [attachmentBehavior setDamping:0.1];
        [attachmentBehavior setFrequency:5];
        [self.animator addBehavior:attachmentBehavior];
    }else  {
        
        // 移除之前的所有行为
        [self.animator removeAllBehaviors];
        
        rec.view.center = CGPointMake(endX, endY);
    }

    //拖动完之后，每次都要用setTranslation:方法制0这样才不至于不受控制般滑动出视图
    [rec setTranslation:CGPointMake(0, 0) inView:self];
}