使用滑块控制 nslayoutConstraint 的宽度和高度

Posted 2023-02-23

【中文标题】使用滑块控制 nslayoutConstraint 的宽度和高度

【英文标题】：Use slider to control width and height of a nslayoutConstraint

【发布时间】：2019-12-07 03:38:15

【问题描述】：

我的代码在 swift 中，我想使用滑块 (sd) 来控制 imageview pic 的宽度和高度。我在下面尝试的方法不起作用。只要我移动滑块 sd 和 pic disaper。当滑块移动图片时，应该逐渐改变它的宽度和高度。我在调试区域看到了百分比变化，但它在图片上不起作用。我的代码不使用情节提要。

import UIKit

class ViewController: UIViewController 
var sd = UISlider()
var pic = UIImageView()
var start = [NSLayoutConstraint]()
var change = [NSLayoutConstraint]()

override func viewDidLoad() 
    super.viewDidLoad()
    // Do any additional setup after loading the view.

    [sd,pic].forEach
        $0.translatesAutoresizingMaskIntoConstraints = false
        view.addSubview($0)

        $0.backgroundColor = .systemOrange
    

    start = [
        pic.trailingAnchor.constraint(equalTo: view.centerXAnchor, constant :150),
        pic.topAnchor.constraint(equalTo: view.centerYAnchor, constant : -225),
        pic.widthAnchor.constraint(equalToConstant: 300),
        pic.heightAnchor.constraint(equalToConstant: 450),

        sd.trailingAnchor.constraint(equalTo: view.centerXAnchor, constant :150),
        sd.topAnchor.constraint(equalTo: view.centerYAnchor, constant : +250),
        sd.widthAnchor.constraint(equalToConstant: 100),
        sd.heightAnchor.constraint(equalToConstant: 40)
    ]
    NSLayoutConstraint.activate(start)

    sd.addTarget(self, action: #selector(moveRight), for: .allEvents)








@objc func moveRight() 

        NSLayoutConstraint.deactivate(start)

    let jessicaAlba = CGFloat(sd.value)
    print(jessicaAlba)


    NSLayoutConstraint.activate ([

        pic.trailingAnchor.constraint(equalTo: view.centerXAnchor, constant :150),
        pic.topAnchor.constraint(equalTo: view.centerYAnchor, constant : -225),
        pic.widthAnchor.constraint(equalToConstant: jessicaAlba),
        pic.heightAnchor.constraint(equalToConstant: jessicaAlba),

        sd.trailingAnchor.constraint(equalTo: view.centerXAnchor, constant :150),
        sd.topAnchor.constraint(equalTo: view.centerYAnchor, constant : +250),
        sd.widthAnchor.constraint(equalToConstant: 100),
        sd.heightAnchor.constraint(equalToConstant: 40)

    ])
      NSLayoutConstraint.activate(change)

【参考方案1】：

您的代码有两个问题。

1 ) 您已将 widthAnchor 和 heightAnchor 约束设置为 CGFloat(sd.value) 的常量，范围在 0 到 1 之间。这就是为什么您的图片似乎消失了。但实际上，它的宽度和高度被设置为小于 1 的值。

2 ) 您尚未从 moveRight 函数停用先前设置的约束。

试试下面的示例 sn-p，

    @objc func moveRight() 
        NSLayoutConstraint.deactivate(start)

        let jessicaAlba = 300 + ( 300 * CGFloat(sd.value) )
        print(CGFloat(sd.value))

        start = [

            pic.trailingAnchor.constraint(equalTo: view.centerXAnchor, constant :150),
            pic.topAnchor.constraint(equalTo: view.centerYAnchor, constant : -225),
            pic.widthAnchor.constraint(equalToConstant: jessicaAlba),
            pic.heightAnchor.constraint(equalToConstant: jessicaAlba),

            sd.trailingAnchor.constraint(equalTo: view.centerXAnchor, constant :150),
            sd.topAnchor.constraint(equalTo: view.centerYAnchor, constant : +250),
            sd.widthAnchor.constraint(equalToConstant: 100),
            sd.heightAnchor.constraint(equalToConstant: 40)

        ]
        NSLayoutConstraint.activate (start)