最近實現了下tableViewCell視覺差效果，分享一波。

效果圖.gif

原理

圖1.png

<pre>自定義cell，需要一張大于contentView的圖片，并且設置好相應約束。
coverImageView 和 centerYConstraint 作為 IBOutlet。
在tableView滾動的時候通過協議方法向cell發送通知，cell收到消息改變constraint實現效果。</pre>

具體實現

//需要使用到的成員變量
@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()
        //設置代理，往數據源加入數據
        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 {
        //注冊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 {
        //設置高度
        return 9 / 16 * UIScreen.mainScreen().bounds.size.width
    }


func tableView(tableView: UITableView, willDisplayCell cell: UITableViewCell, forRowAtIndexPath indexPath: NSIndexPath) {
        //當需要顯示cell時調用，填充數據
        let cell:MyTableViewCell = cell as! MyTableViewCell
        cell.coverImageView.image = self.dataArray[indexPath.row] as? UIImage
    }

//通過lastPoint.y和contentOffset.y進行比較可以得出滑動方向，往cell發送通知
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的成員變量
@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的內容
        self.contentView.clipsToBounds = true
        self.clipsToBounds = true
        //計算y軸中心約束可移動的最大范圍絕對值
        constantGap = (2/1) * self.contentView.bounds.size.width / 2 - self.contentView.bounds.size.height/2
        //注冊通知
        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
        //通過傳來的參數判斷滑動方向，實時改變約束值
        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)
    }

代碼Demo