Swift PanGesture :问题管理约束:新盘闪现

Question

这是用于控制具有泛功能视图的视图的代码.

import UIKit

class ViewController: UIViewController {

    @IBOutlet weak var redRect: PaletteView!
    @IBOutlet var paletteTop : NSLayoutConstraint?
    @IBOutlet var paletteLeading : NSLayoutConstraint?
    
    override func viewDidLoad() {
        super.viewDidLoad()
        addRedViewUI(tgt: redRect!)
        redRect.addGestureRecognizer(UIPanGestureRecognizer(target: self, action: #selector(palettePan(_:))))
        redRect?.translatesAutoresizingMaskIntoConstraints = false
        NSLayoutConstraint.activate(paletteConstraints())
    }
    
    func addRedViewUI(tgt : PaletteView) {
        var pos = CGPoint(x: 10, y: 10)
        var size = CGSize(width: 200, height: 240)
        var v = UIView(frame: CGRect(origin: pos, size: size))
        v.backgroundColor = .black
        tgt.addSubview(v)
    }
    
    func paletteConstraints() -> Array<NSLayoutConstraint> {
        var constraints : Array<NSLayoutConstraint> = []
        constraints.append((redRect?.leadingAnchor.constraint( equalTo: view.leadingAnchor, constant: 100))!)
        paletteLeading = constraints.last
        constraints.append((redRect?.topAnchor.constraint( equalTo: view.topAnchor, constant: 100))!)
        paletteTop = constraints.last
        constraints.append((redRect?.widthAnchor.constraint(equalToConstant: 250))! )
        constraints.append((redRect?.heightAnchor.constraint(equalToConstant: 350))! )
        return constraints
    }
    
    func paletteConstraints(_ tgtView : PaletteView ) -> Array<NSLayoutConstraint> {
        var constraints : Array<NSLayoutConstraint> = []
        constraints.append((tgtView.leadingAnchor.constraint( equalTo: redRect!.leadingAnchor)))
        constraints.append((tgtView.topAnchor.constraint( equalTo: redRect!.topAnchor)))
        return constraints
    }
    
    @objc func palettePan(_ sender: UIPanGestureRecognizer) {
        let translation = sender.translation(in: view)
        switch sender.state {
        case .began:
            print("start \(redRect!.frame)")
            paletteLeading?.constant = redRect!.frame.origin.x
            paletteTop?.constant = redRect!.frame.origin.y
        case .changed:
            redRect!.transform = CGAffineTransform(translationX: translation.x, y: translation.y)
        case .ended:
            print("done \(redRect!.frame)")
        default:
            _ = true
        }
    }
}

class PaletteView : UIView {
    var lastPos: CGPoint = CGPoint(x: 20, y: 20)
    
    convenience init() {
        self.init(frame: CGRect(x: 10, y: 10, width: 200, height: 200))
        translatesAutoresizingMaskIntoConstraints = false
    }
}

它的工作很好，除了当开始一个新的锅，它从它的位置从最后一个锅结束，然后立即跳回来和锅可以完成。这个跳转的方向和最后一个平底锅是一样的，所以第二个平底锅--视图不会跳，然后平底锅--它跳到最后一个平底锅的方向上，数量大致相同。

这让我觉得这是与发送者状态相关的东西，但我不知道是什么。如果最后一个平底锅的数量很小，或者是开始缓慢，没有闪光灯，但我还不知道它是从哪里来的。

被平移的视图在storyBoard中没有约束，但它确实被定义并连接到故事板中的输出端。

Answer 1

解决方案是更改函数，以便在发生更改的情况下更新约束之后，启动和更改CGAffineTransform：

@objc func palettePan(_ sender: UIPanGestureRecognizer) {
        let translation = sender.translation(in: view)
        switch sender.state {
        case .began:
            print("start \(redRect!.frame)")
            paletteLeading?.constant = redRect!.frame.origin.x
            paletteTop?.constant = redRect!.frame.origin.y
            redRect!.transform = CGAffineTransform(translationX: translation.x, y: translation.y)
        case .changed:
            redRect!.transform = CGAffineTransform(translationX: translation.x, y: translation.y)
        case .ended:
            print("done \(redRect!.frame)")
        default:
            _ = true
        }
    }