如何以编程方式设置控制图像视图宽度的滑块答案

【问题标题】：How to programmatically set a slider that controls a image views width如何以编程方式设置控制图像视图宽度的滑块
【发布时间】：2019-11-17 05:34:16
【问题描述】：

我下面的代码是用没有故事板的所有代码编写的。我想要做的是使用滑块移动来更改 imageView pic 的宽度。我在下面尝试过的不起作用。当滑块移动时，我希望图片的宽度随之移动。

import UIKit

class ViewController: UIViewController {

    var pic = UIImageView()
    var move = UISlider()

    var oldCons = [NSLayoutConstraint]()
    var box = 20
    override func viewDidAppear(_ animated: Bool) {
        super.viewDidAppear(animated)
        pic.backgroundColor = UIColor.systemYellow

           [pic,move].forEach({
               $0.translatesAutoresizingMaskIntoConstraints = false
               self.view.addSubview($0)
           })

        oldCons = [
               pic.trailingAnchor.constraint(equalTo: view.centerXAnchor, constant :150),
               pic.topAnchor.constraint(equalTo: view.centerYAnchor, constant : -200),
               pic.widthAnchor.constraint(equalToConstant: CGFloat(box)),
               pic.heightAnchor.constraint(equalToConstant: 450)
            ]
           NSLayoutConstraint.activate(oldCons)

           NSLayoutConstraint.activate ([
               move.trailingAnchor.constraint(equalTo: view.centerXAnchor, constant :37.5),
               move.topAnchor.constraint(equalTo: view.centerYAnchor, constant : 225),
               move.widthAnchor.constraint(equalToConstant: 200),
               move.heightAnchor.constraint(equalToConstant: 50),

           ])
           move.addTarget(self, action: #selector(moveRight), for: .touchUpInside)
    }

    @objc func moveRight() {
        NSLayoutConstraint.deactivate(oldCons)
        NSLayoutConstraint.activate ([
            pic.trailingAnchor.constraint(equalTo: view.centerXAnchor, constant :50),
            pic.topAnchor.constraint(equalTo: view.centerYAnchor, constant : -50),
            pic.widthAnchor.constraint(equalToConstant: CGFloat(box)),
            pic.heightAnchor.constraint(equalToConstant: 450)
        ])

        box = Int(CGFloat(20 + move.value*90))
        print(box)
    }
}

【问题讨论】：

标签： swift slider nslayoutconstraint func viewdidappear

【解决方案1】：

添加picWidthConstraint 作为类级属性，而不是激活/停用约束集：

    // we'll use this to dynamically change the pic width
    var picWidthConstraint: NSLayoutConstraint!

那么，当你想改变pic的宽度时，改变那个约束的.constant：

    box = Int(CGFloat(20 + move.value*90))
    print(box)
    picWidthConstraint.constant = CGFloat(box)

这是您的原始课程，经过修改（参见 cmets）：

import UIKit

class ViewController: UIViewController {

    var pic = UIImageView()
    var move = UISlider()

    // don't need this anymore
    //var oldCons = [NSLayoutConstraint]()

    var box = 20

    // we'll use this to dynamically change the pic width
    var picWidthConstraint: NSLayoutConstraint!

    override func viewDidAppear(_ animated: Bool) {
        super.viewDidAppear(animated)
        pic.backgroundColor = UIColor.systemYellow

        [pic,move].forEach({
            $0.translatesAutoresizingMaskIntoConstraints = false
            self.view.addSubview($0)
        })

        // create pic.widthAnchor property (var)
        picWidthConstraint = pic.widthAnchor.constraint(equalToConstant: CGFloat(box))

        NSLayoutConstraint.activate ([
            pic.trailingAnchor.constraint(equalTo: view.centerXAnchor, constant :150),
            pic.topAnchor.constraint(equalTo: view.centerYAnchor, constant : -200),

            // activate the pic width constraint
            picWidthConstraint,

            // don't create another one
            //pic.widthAnchor.constraint(equalToConstant: CGFloat(box)),

            pic.heightAnchor.constraint(equalToConstant: 450),

            // constraints for the slider
            move.trailingAnchor.constraint(equalTo: view.centerXAnchor, constant :37.5),
            move.topAnchor.constraint(equalTo: view.centerYAnchor, constant : 225),
            move.widthAnchor.constraint(equalToConstant: 200),
            move.heightAnchor.constraint(equalToConstant: 50),

        ])

        // use .valueChanged to change the pic width *while* dragging the slider thumb
//      move.addTarget(self, action: #selector(moveRight), for: .touchUpInside)
        move.addTarget(self, action: #selector(moveRight), for: .valueChanged)

    }

    @objc func moveRight() {

        box = Int(CGFloat(20 + move.value*90))
        print(box)
        picWidthConstraint.constant = CGFloat(box)

    }

}

【讨论】：