iOS Review | UIGestureRecognizer

UIGestureRecognizer共有8种：

• UITapGestureRecognizer
• UIPanGestureRecognizerpan
• UIScreenEdgePanRecognizer
• UIPinchGestureRecognizer
• UIRotationGestureRecognizer
• UILongPressGestureRecognizer
• UISwipeGestureRecognizer
• UIGestureRecognizer即自定义手势

其用法大同小异，比较常用的主要有tap和pan，主要使用recognizer.location和recognizer.view属性。

Storyboard上添加手势

UIPanGestureRecognizer

利用UIPanGesgtureRecognizer让view跟随touch移动，通常有两种处理逻辑。

• 第一种利用recognizer.location：

var offset: CGSize! // 记住一开始的touch point距离center的偏移值

// 事件回调
@IBAction func handlePan(recognizer : UIPanGestureRecognizer) {
    let location = recognizer.location(in: view)
    guard let view = recognizer.view else {
        return
    }
    switch recognizer.state {
        case .began:
// 计算并存储偏移值
            offset = CGSize(width: view.center.x - location.x, height: view.center.y - location.y)
// 偏移值 + location值即可做到跟随移动
        case .changed:
            view.center = CGPoint(x: offset.width + location.x, y: offset.height + location.y)
        default: break
    }
}

recognizer.location

这种方式虽然理解起来简单，但处理逻辑稍微繁琐点，不推荐使用。

• 第一种利用recognizer.translation：

@IBAction func handlePan(recognizer : UIPanGestureRecognizer) { 
// pan的移动偏移量--相对began时的点
    let translation = recognizer.translation(in: view)
    if let view = recognizer.view {
        view.center = CGPoint(x: view.center.x + translation.x, y: view.center.y + translation.y)
    }
// 在移动changed时，重置pan的上一次移动点为zero
    recognizer.setTranslation(.zero, in: view)
}

这种方式虽然使用简单，但要注意每次recognizer.setTranslation(.zero)归零，不然，一下子就让view移出了屏幕，因为translation每次就compound叠加的。

• pan手势滑动的加速度velocity：

if recognizer.state == .ended {
// 加速度
    let velocity = recognizer.velocity(in: self.view)
    let magnitude = sqrt(velocity.x * velocity.x + velocity.y * velocity.y)
    let slideMultiplier = magnitude / 200
    let slideFactor = 0.1 * slideMultiplier
    
// 最终点
    var finalPoint = CGPoint(x: view.center.x + (velocity.x * slideFactor), y: view.center.y + (velocity.y * slideFactor))
    let halfWidth = panView.bounds.width / 2
    let halfHeight = panView.bounds.height / 2
    finalPoint.x = min(self.view.bounds.width - halfWidth, max(halfWidth, finalPoint.x))
    finalPoint.y = min(self.view.bounds.height - halfHeight, max(halfHeight, finalPoint.y))
    
// 动画
    UIView.animate(withDuration: Double(slideFactor * 2), delay: 0, options: .curveEaseInOut, animations: {
        panView.center = finalPoint
    }, completion: nil)
}

加速度动画

UIPinchGestureRecognizer

• 使用比较简单，利用recognizer.scale值即可transform要scale的view，但注意scale值也是连续变化的，注意随时将recognizer.scale归零。

  @IBAction func handlePinch(recognizer : UIPinchGestureRecognizer) {
    guard let pinchView = recognizer.view else {
        return
    }
    let scale = recognizer.scale
    pinchView.transform = pinchView.transform.scaledBy(x: scale, y: scale)
    recognizer.scale = 1 // 归零
  }

UIRotationGestureRecognizer

• 使用和UIPinchGestureRecognizer一样，利用recognizer.rotation值即可transform要rotate的view，但注意rotation值也是连续变化的，注意随时将recognizer.rotation归零。

  @IBAction func handleRotate(recognizer : UIRotationGestureRecognizer) {
    guard let rotateView = recognizer.view else {
        return
    }
    let rotation = recognizer.rotation
    rotateView.transform = rotateView.transform.rotated(by: rotation)
    recognizer.rotation = 0
  }

Simultaneous Gesture Recognizers

• 一般情况下，每个手势只能被单独使用，并不能在执行一个手势如rotation的同时执行scale手势，但可以设置UIGestureRecognizer的delegate，来配置是否允许手势同时执行。

extension ViewController: UIGestureRecognizerDelegate{
    func gestureRecognizer(_ gestureRecognizer: UIGestureRecognizer, shouldRecognizeSimultaneouslyWith otherGestureRecognizer: UIGestureRecognizer) -> Bool {
        return true
    }
}

UITapGestureRecognizer

• 这个手势相对来说是最常用的一个，实现方式也简单，常用recognizer.location属性和recognizer.view判断点击的view是否是目标view，然后处理不同的逻辑。

var chompPlayer: AVAudioPlayer? = nil
    
  override func viewDidLoad() {
    super.viewDidLoad()
    
    let filteredSubviews = view.subviews.filter{
        $0 is UIImageView
    }
// 给所有UIImageView添加tap手势
    for subview in filteredSubviews {
        let tapGestureRecognizer = UITapGestureRecognizer(target: self, action: #selector(handleTap(recognizer:)))
        tapGestureRecognizer.delegate = self
        subview.addGestureRecognizer(tapGestureRecognizer)

// TODO:
    }
    
    chompPlayer = loadSound(filename: "chomp")
  }

// tap手势处理
@objc func handleTap(recognizer: UITapGestureRecognizer) {
    chompPlayer?.play()
  }

• 但注意以上tap手势和pan手势会同时执行，在pan很小值得时候，tap手势也会被触发，这种情况下可以用recognizer.require(toFail:)让2个冲突的手势只能执行一个。

// TODO:
tapGestureRecognizer.require(toFail: panGestureRecognizer)

Custom UIGestureRecognizer

• 基于UIGestureRecognizer的自定义手势，注意在Swift中，需要借助OC桥接.h文件，才能重写touches等事件方法。

1. 新建OC-Header桥接文件，并导入头文件。

#import <UIKit/UIGestureRecognizerSubclass.h>

2. 新建类，实现touchesBegan、moved、ended、canceled等方法。

"挠痒痒"自定义手势

class TickleGestureRecognizer: UIGestureRecognizer {
    enum Direction: String {
        case unknown = "DirectionUnknown", 
        left = "DirectionLeft", 
        right = "DirectionRight"
    }
    var requiredTickles = 2
    var distanceForTickleGesture: CGFloat = 25
    
    var tickleCount = 0
    var lastDirection: Direction = .unknown
    var curTickleStart: CGPoint = .zero
    
    override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent) {
        guard let touch = touches.first else {
            return
        }
        curTickleStart = touch.location(in: view)
    }
    
    override func touchesMoved(_ touches: Set<UITouch>, with event: UIEvent) {
        guard let touch = touches.first else {
            return
        }
        let ticklePoint = touch.location(in: view)
        let moveAmt = ticklePoint.x - curTickleStart.x 
        var curDirection: Direction = .unknown
        if moveAmt < 0 {
            curDirection = .left
        }
        else{
            curDirection = .right
        }
        if fabs(moveAmt) < distanceForTickleGesture {
            return
        }
        
        if (lastDirection == .left && curDirection == .right) ||
            (lastDirection == .right && curDirection == .left) || 
            lastDirection == .unknown{
            tickleCount += 1
            curTickleStart = ticklePoint
            lastDirection = curDirection
            
            if state == .possible && tickleCount > requiredTickles{
                print("He He He...")
                state = .ended
            }
        }
        
        print("\(curDirection.rawValue)")
    }
    
    override func touchesEnded(_ touches: Set<UITouch>, with event: UIEvent) {
        reset()
    }
    
    override func touchesCancelled(_ touches: Set<UITouch>, with event: UIEvent) {
        reset()
    }
    
    override func reset() {
        curTickleStart = .zero
        lastDirection = .unknown
        tickleCount = 0
        if state == .possible {
            state = .failed
        }
    }
}

3. 使用自定义手势

let tickleGestureRecognizer = TickleGestureRecognizer(target: self, action: #selector(handleTickle(recognizer:)))
subview.addGestureRecognizer(tickleGestureRecognizer)

@objc func handleTickle(recognizer: TickleGestureRecognizer) {
    hehePlayer?.play()
}

也可以在storyboard上使用自定义手势

UILongPressGestureRecognizer

长按手势

UIScreenEdgePanGestureRecognizer

屏幕边缘滑动手势

UISwipeGestureRecognizer

扫除手势

• 支持单点和多点手势，设置numberOfTouchesRequired属性。
• 判断方向通过direction属性，主要有up、down、left、right。
• 可以通过recognizer.location进行子view的translation变换。