addSubview 在 UIView 中不起作用 - Swift 编程

Question

我需要在 UIView 上添加一个 UIButton 作为子视图，但它实际上并没有在运行时出现。 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
    
    
}

按钮最终不会添加到视图中。我确信这是一个简单的解决方法，但我无法理解它。

Answer 1

首先，确保 viewController 显示任何内容，因为您在没有情节提要的情况下执行此操作，请查看这个简单的教程：

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

如果问题出在那个 UIButton 上，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leadingAnchor 约束，这也可能是问题所在。