Swift Pangesture：管理约束：在新锅上闪烁的问题

Question

这是用于控制具有PAN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
    }
}

它可以正常工作，除了在开始新的锅时，它从最后一个锅的末端从其位置跳下来，然后瞬间跳回并可以完成锅。这种跳跃的方向与最后一个平底锅相同，因此第二个锅不会跳跃，随后的盘子朝着最后一个锅走的方向跳跃，大致相同。

这使我认为这与发件人状态相关，但我不知道什么。如果最后一个锅的数量很小，或者锅开始缓慢，则没有闪光灯，但是我无法理解它来自哪里。

情节板中没有限制的视图，但确实可以定义并连接到情节提要中的插座。

Answer 1

解决方案是更改函数，以便在更改约束之后启动和更改执行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
        }
    }