最近实现了下tableViewCell视觉差效果，分享一波。

效果图.gif

原理

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图1.png

<pre>自定义cell，需要一张大于contentView的图片，并且设置好相应约束。
coverImageView 和 centerYConstraint 作为 IBOutlet。
在tableView滚动的时候通过协议方法向cell发送通知，cell收到消息改变constraint实现效果。</pre>

具体实现

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//需要使用到的成员变量
@IBOutlet weak var tableView: UITableView!    
var dataArray:NSMutableArray = NSMutableArray()
var once:dispatch_once_t = 0
var lastPoint:CGPoint = CGPoint(x: 0, y: 0)

override func viewDidLoad() {
        super.viewDidLoad()
        //设置代理，往数据源加入数据
        self.tableView.delegate = self
        self.tableView.dataSource = self
        self.tableView.separatorStyle = .None
        for index in 1...9 {
            let image:UIImage = UIImage(named: "\(index).jpg")!
            self.dataArray.addObject(image);
        }
    }

func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {
        //注册Nib
        dispatch_once(&once) { 
            tableView.registerNib(UINib(nibName: "MyTableViewCell", bundle: NSBundle.mainBundle()), forCellReuseIdentifier: "CELL")
        }
        let cell:MyTableViewCell = tableView.dequeueReusableCellWithIdentifier("CELL", forIndexPath: indexPath) as! MyTableViewCell
        return cell
    }

func tableView(tableView: UITableView, heightForRowAtIndexPath indexPath: NSIndexPath) -> CGFloat {
        //设置高度
        return 9 / 16 * UIScreen.mainScreen().bounds.size.width
    }


func tableView(tableView: UITableView, willDisplayCell cell: UITableViewCell, forRowAtIndexPath indexPath: NSIndexPath) {
        //当需要显示cell时调用，填充数据
        let cell:MyTableViewCell = cell as! MyTableViewCell
        cell.coverImageView.image = self.dataArray[indexPath.row] as? UIImage
    }

//通过lastPoint.y和contentOffset.y进行比较可以得出滑动方向，往cell发送通知
func scrollViewDidScroll(scrollView: UIScrollView) {
        var directionStr:String = ""
        if lastPoint.y > scrollView.contentOffset.y {
            directionStr = "Up"
        } else if lastPoint.y < scrollView.contentOffset.y {
            directionStr = "Down"
        }
        lastPoint = scrollView.contentOffset
        NSNotificationCenter.defaultCenter().postNotificationName("ScrollViewAnimation", object: directionStr)
    }

//cell的成员变量
@IBOutlet weak var coverImageView: UIImageView!
@IBOutlet weak var centerYConstraint: NSLayoutConstraint!
var constantGap:CGFloat = 0.0

override func awakeFromNib() {
        super.awakeFromNib()
        //剪裁掉超出cell的内容
        self.contentView.clipsToBounds = true
        self.clipsToBounds = true
        //计算y轴中心约束可移动的最大范围绝对值
        constantGap = (2/1) * self.contentView.bounds.size.width / 2 - self.contentView.bounds.size.height/2
        //注册通知
        NSNotificationCenter.defaultCenter().addObserver(self, selector: #selector(MyTableViewCell.scrollViewAnimation), name: "ScrollViewAnimation", object: nil)
    }

func scrollViewAnimation(notification:NSNotification) {
        let directionStr:String = notification.object as! String
        var constant:CGFloat = self.centerYConstraint.constant
        //通过传来的参数判断滑动方向，实时改变约束值
        if directionStr == "Up" {
            if constant < constantGap {
                constant += 1
            } else  if constant > constantGap {
                constant = constantGap
            }
            self.centerYConstraint.constant = constant
        } else if directionStr == "Down" {
            if constant > -1 * constantGap {
                constant -= 1
            } else  if constant < -1 * constantGap {
                constant = -1 * constantGap
            }
            self.centerYConstraint.constant = constant
        }
    }

//移除通知
deinit {
        NSNotificationCenter.defaultCenter().removeObserver(self)
    }

代码Demo