约束对象以防止对象更改大小时移动它们

Posted 2021-04-19

正如您在下面的gif中所看到的，当幻灯片上深绿色对象的大小增加时，浅绿色对象将向南移动。我想做的是，当增加深绿色的对象大小时，浅绿色的对象不会移动，它保持在原位置。即使图像不动，也会发生相同的情况。

import UIKit

class ViewController: UIViewController {



    var picWidth: NSLayoutConstraint!
    var picHeight: NSLayoutConstraint!
    var pic = UIImageView()
    var slider = UISlider()
    var pic2 = UIImageView()
    var existingTransition : CGAffineTransform?

    var currentView: UIView?

    var g2 = UIPanGestureRecognizer()



    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view.
        pic.isUserInteractionEnabled = true

        g2 = UIPanGestureRecognizer(target: self, action: #selector(ViewController.g1Method))
        pic.addGestureRecognizer(g2)

        pic.backgroundColor = .systemGreen
        pic2.backgroundColor = .green

        picWidth =  pic.widthAnchor.constraint(equalTo:  view.widthAnchor ,multiplier:  0.2)
        picHeight =  pic.heightAnchor.constraint(equalTo:  view.heightAnchor ,multiplier:  0.20)
        [pic,pic2,slider].forEach {

            view.addSubview($0)
            $0.translatesAutoresizingMaskIntoConstraints = false

        }
        NSLayoutConstraint.activate ([
            pic.topAnchor.constraint(equalTo: view.topAnchor, constant : 0),
            picWidth,
            picHeight,
            pic.leadingAnchor.constraint(equalTo: view.leadingAnchor, constant :0),

            pic2.topAnchor.constraint(equalTo: pic.bottomAnchor, constant : 0),
            pic2.heightAnchor.constraint(equalTo: view.heightAnchor, multiplier: 0.5, constant: 0),
            pic2.widthAnchor.constraint(equalTo: view.widthAnchor, multiplier: 0.4, constant: 0),
            pic2.leadingAnchor.constraint(equalTo: view.leadingAnchor, constant : 0),


            slider.topAnchor.constraint(equalTo: pic2.bottomAnchor, constant : 0),
            slider.heightAnchor.constraint(equalTo: view.heightAnchor, multiplier: 0.20, constant: 0),
            slider.widthAnchor.constraint(equalTo: view.widthAnchor, multiplier: 0.20, constant: 0),
            slider.leadingAnchor.constraint(equalTo: view.leadingAnchor, constant : 0),


        ])

        slider.addTarget(self, action: #selector(hhh), for: .allEvents)


    }
    @objc func handleTapGestured(_ gesture: UIPanGestureRecognizer) {
        currentView = gesture.view
    }

    @objc func g1Method(_ sender: UIPanGestureRecognizer){

        let subview = pic2
        guard let child = sender.view else{return}
        let transitionPoint = sender.translation(in: self.view)
        let newTransition = CGAffineTransform(translationX: transitionPoint.x, y: transitionPoint.y)
        switch sender.state {

        case .ended,.cancelled:// on End
            if let existing = existingTransition{
                self.existingTransition = newTransition.concatenating(existing)
            }else{
                self.existingTransition = newTransition
            }
        default://on change and other states
            if let existing = existingTransition{
                child.transform = newTransition
                    .concatenating(existing)
            }else{
                child.transform = newTransition
            }
        }
        self.view.layoutIfNeeded()


        let tapGesture = UITapGestureRecognizer(target: self, action: #selector(handleTapGestured(_:)))
        subview.addGestureRecognizer(tapGesture)


    }
    @objc func hhh() {


        picWidth.constant = CGFloat(slider.value) * view.frame.size.width * 0.25
        picHeight.constant = CGFloat(slider.value) * view.frame.size.height * 0.25

    }

}

答案

您的问题在这里：

pic2.topAnchor.constraint(equalTo: pic.bottomAnchor, constant : 0)

您正在告诉布局将pic2形状的顶部与pic形状的底部保持相等。

[要解决此问题，将pic2限制在顶部安全空间，然后将pic的高度限制为常数，以将pic2的顶部直接置于pic之下。

pic2.topAnchor.constraint(equalTo: view.topAnchor, constant : pic.bounds.height)

编辑：pic.bounds.height无法加载，因为您正在同时加载所有viewDidLoad中的约束，并且ViewController尚未放置子视图，因此，当调用pic时，您的pic.bounds.height为null 。为了解决此问题，您需要执行以下操作：

•在viewDidLoad中隔离图片初始化：

override func viewDidLoad() {
    super.viewDidLoad()
    // Do any additional setup after loading the view.
    pic.isUserInteractionEnabled = true

    g2 = UIPanGestureRecognizer(target: self, action: #selector(ViewController.g1Method))
    pic.addGestureRecognizer(g2)

    pic.backgroundColor = .systemGreen
    pic2.backgroundColor = .green

    picWidth =  pic.widthAnchor.constraint(equalTo:  view.widthAnchor ,multiplier:  0.2)
    picHeight =  pic.heightAnchor.constraint(equalTo:  view.heightAnchor ,multiplier:  0.20)
    [pic,pic2,slider].forEach {

        view.addSubview($0)
        $0.translatesAutoresizingMaskIntoConstraints = false

    }
    NSLayoutConstraint.activate([pic.topAnchor.constraint(equalTo: view.topAnchor, constant : 0),
    picWidth,
    picHeight,
    pic.leadingAnchor.constraint(equalTo: view.leadingAnchor, constant :0)])
    slider.addTarget(self, action: #selector(hhh), for: .allEvents)

}

•将其余的所有init放入viewDidLayoutSubviews：

override func viewDidLayoutSubviews() {
    NSLayoutConstraint.activate ([

        pic2.topAnchor.constraint(equalTo: view.topAnchor, constant : pic.bounds.height),
        pic2.heightAnchor.constraint(equalTo: view.heightAnchor, multiplier: 0.5, constant: 0),
        pic2.widthAnchor.constraint(equalTo: view.widthAnchor, multiplier: 0.4, constant: 0),
        pic2.leadingAnchor.constraint(equalTo: view.leadingAnchor, constant : 0),


        slider.topAnchor.constraint(equalTo: pic2.bottomAnchor, constant : 0),
        slider.heightAnchor.constraint(equalTo: view.heightAnchor, multiplier: 0.20, constant: 0),
        slider.widthAnchor.constraint(equalTo: view.widthAnchor, multiplier: 0.20, constant: 0),
        slider.leadingAnchor.constraint(equalTo: view.leadingAnchor, constant : 0),


    ])
}

作为一个旁注，如果要使浅绿色方块移动，则滑块仍然会被弄乱，因为您将其限制在方块上。尝试根据视图的锚点而不是其他UI元素来限制对位于屏幕外部的对象的约束。