addSubview在UIView中不起作用-以编程方式快速

问题描述

我需要在UIView上添加一个UIButton作为子视图，但实际上它不会在运行时出现。 这是我的代码：

let moreButton : UIButton = {
    let button = UIButton()
    button.setimage(#imageLiteral(resourceName: "more"),for: .normal)
    button.translatesAutoresizingMaskIntoConstraints = false
    return button
}()

 override init(frame: CGRect) {
    super.init(frame: frame)
    
    addSubview(moreButton)
    moreButton.trailingAnchor.constraint(equalTo: self.trailingAnchor).isActive = true
    moreButton.topAnchor.constraint(equalTo: self.topAnchor).isActive = true
    moreButton.heightAnchor.constraint(equalToConstant: 30).isActive = true
    moreButton.widthAnchor.constraint(equalToConstant: 20).isActive = true
    
    
}

该按钮最终不会添加到视图中。我敢肯定，这是一个简单的解决方法，但是我无法解决这个问题。

解决方法

首先，请确保您在没有情节提要的情况下，viewController正在显示任何内容，请查看以下简单教程：

https://medium.com/better-programming/creating-a-project-without-storyboard-in-2020-and-without-swifui-82080eb6d13b

如果问题在于该UIButton，请尝试在viewDidLoad中设置子视图：

final class ViewController: UIViewController {

let cardView = CardView()

override func viewDidLoad() {
    super.viewDidLoad()
    
    view.addSubview(cardView)
    
    /// Constraints
    let margins = view.layoutMarginsGuide
    cardView.trailingAnchor.constraint(equalTo: margins.trailingAnchor).isActive = true
    cardView.leadingAnchor.constraint(equalTo: margins.leadingAnchor).isActive = true
    cardView.topAnchor.constraint(equalTo: margins.topAnchor).isActive = true
    cardView.heightAnchor.constraint(equalToConstant: 30).isActive = true
    cardView.widthAnchor.constraint(equalToConstant: 20).isActive = true
}

}

final class CardView: UIView {

let moreButton : UIButton = {
    let button = UIButton()
    button.setTitle("Button title",for: .normal)
    button.translatesAutoresizingMaskIntoConstraints = false
    return button
}()

required init(coder aDecoder: NSCoder) {
    super.init(coder: aDecoder)!
}

override init(frame: CGRect) {
    super.init(frame:frame)
    
    self.translatesAutoresizingMaskIntoConstraints = false
    
    self.addSubview(moreButton)
    
    /// Constraints
    let margins = self.layoutMarginsGuide
    moreButton.trailingAnchor.constraint(equalTo: margins.trailingAnchor).isActive = true
    moreButton.leadingAnchor.constraint(equalTo: margins.leadingAnchor).isActive = true
    moreButton.topAnchor.constraint(equalTo: margins.topAnchor).isActive = true
    moreButton.heightAnchor.constraint(equalToConstant: 30).isActive = true
    moreButton.widthAnchor.constraint(equalToConstant: 20).isActive = true
}
}

我已经为约束设置了边距，还添加了一个leadAnchor约束，这可能也是问题所在。