滑块仅增加 imageview 大小而不减小大小

Question

我的 swift 下面的代码使用滑块来增加图像视图的大小。我想做的是当滑块从小于 0.5 移动时，图像视图变小。如果滑块的值等于或大于 0.5，则 imageveiw 的大小会增加。现在滑块值设置为 0.5

import UIKit

class ViewController: UIViewController {



    var image1Width2: NSLayoutConstraint!
    var image1Height2: NSLayoutConstraint!

    var slider = UISlider()
    var blueMove = UIImageView()


    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view.
        slider.value = 0.5
        blueMove.backgroundColor = .blue

        blueMove.isUserInteractionEnabled = true




     blueMove.backgroundColor = .blue


        [blueMove,slider].forEach {

            view.addSubview([=10=])
            [=10=].translatesAutoresizingMaskIntoConstraints = false

        }

        //image12
        image1Width2 =  blueMove.widthAnchor.constraint(equalTo:  view.widthAnchor ,multiplier:  0.25)
        image1Height2 =  blueMove.heightAnchor.constraint(equalTo:  view.heightAnchor ,multiplier:  0.20)



        let percent1 = self.view.frame.height * 0.1

        let percent2 = self.view.frame.width * 0.2


        NSLayoutConstraint.activate([


            blueMove.topAnchor.constraint(equalTo: view.topAnchor, constant : percent1),

            image1Width2,
            image1Height2,

            blueMove.leadingAnchor.constraint(equalTo: view.leadingAnchor, constant :percent2)
        ])







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

    }

        override func viewDidLayoutSubviews() {
            NSLayoutConstraint.activate ([


      slider.bottomAnchor.constraint(equalTo: view.bottomAnchor),

                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),


            ])
        }

    @objc func hhh() {



            image1Width2.constant = CGFloat(slider.value) * view.frame.size.width * 0.25
            image1Height2.constant = CGFloat(slider.value) * view.frame.size.height * 0.25





    }

}

Answer 1

在 viewDidLoad() 中，您正在根据值为 0.0 的滑块定义 "blue view" 的约束...但是您为滑块提供的初始值为 0.5。

因此，当您第一次触摸滑块时，您的蓝色视图的大小 "jumps" 调整为 0.5 大小。

在viewDidLoad()末尾添加对hhh()的调用：

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

    // change blue view based on initial slider value of 0.5
    hhh()

现在您会看到蓝色视图在向左拖动滑块时变小，在向右拖动时变大。

滑块仅增加 imageview 大小而不减小大小

slider only increasing imageview size not decreasing size

swift

slider

constants

nslayoutconstraint

cgfloat