Swift 从代码中设置约束 - 查看下视图答案

【问题标题】：Swift set constraints from code - View under viewSwift 从代码中设置约束 - 查看下视图
【发布时间】：2020-08-02 17:51:13
【问题描述】：

我正在使用这个扩展方法来设置我的视图锚：

@discardableResult
open func anchor(top: NSLayoutYAxisAnchor?, leading: NSLayoutXAxisAnchor?, bottom: NSLayoutYAxisAnchor?, trailing: NSLayoutXAxisAnchor?, padding: UIEdgeInsets = .zero, size: CGSize = .zero) -> AnchoredConstraints {
    
    translatesAutoresizingMaskIntoConstraints = false
    var anchoredConstraints = AnchoredConstraints()
    
    if let top = top {
        anchoredConstraints.top = topAnchor.constraint(equalTo: top, constant: padding.top)
    }
    
    if let leading = leading {
        anchoredConstraints.leading = leadingAnchor.constraint(equalTo: leading, constant: padding.left)
    }
    
    if let bottom = bottom {
        anchoredConstraints.bottom = bottomAnchor.constraint(equalTo: bottom, constant: -padding.bottom)
    }
    
    if let trailing = trailing {
        anchoredConstraints.trailing = trailingAnchor.constraint(equalTo: trailing, constant: -padding.right)
    }
    
    if size.width != 0 {
        anchoredConstraints.width = widthAnchor.constraint(equalToConstant: size.width)
    }
    
    if size.height != 0 {
        anchoredConstraints.height = heightAnchor.constraint(equalToConstant: size.height)
    }
    
    [anchoredConstraints.top, anchoredConstraints.leading, anchoredConstraints.bottom, anchoredConstraints.trailing, anchoredConstraints.width, anchoredConstraints.height].forEach{ $0?.isActive = true }
    
    return anchoredConstraints
}

在我的应用程序中，我有两个标签，我想在这两个标签下设置一个 UITextField，其中包含以下代码：

widTextLabel.anchor(top: view.safeAreaLayoutGuide.topAnchor, leading: nil, bottom: nil, trailing: nil, padding: .init(top: 0.0, left: 0.0, bottom: 0.0, right: 0.0))
widTextLabel.centerXAnchor.constraint(equalTo: view.centerXAnchor, constant: -70).isActive = true

heiTextLabel.anchor(top: view.safeAreaLayoutGuide.topAnchor, leading: nil, bottom: nil, trailing: nil)
heiTextLabel.centerXAnchor.constraint(equalTo: view.centerXAnchor, constant: 70).isActive = true

widTextField.anchor(top: widTextLabel.bottomAnchor, leading: nil, bottom: nil, trailing: nil, size: .init(width: 50, height: 50))
widTextField.centerXAnchor.constraint(equalTo: widTextLabel.centerXAnchor).isActive = true

heiTextField.anchor(top: heiTextLabel.bottomAnchor, leading: nil, bottom: nil, trailing: nil, size: .init(width: 50, height: 50))
heiTextLabel.centerXAnchor.constraint(equalTo: heiTextLabel.centerXAnchor).isActive = true

我在控制台中收到此错误：

*** Terminating app due to uncaught exception 'NSGenericException', reason: 'Unable to activate constraint with anchors <NSLayoutYAxisAnchor:0x6000015d9b40 "UITextField:0x7fdf8501a800.top"> and <NSLayoutYAxisAnchor:0x6000015d9b00 "UILabel:0x7fdf84e13cd0'test'.bottom"> because they have no common ancestor.  Does the constraint or its anchors reference items in different view hierarchies?  That's illegal.'

【问题讨论】：

例外是对的。 UILabel 测试放在哪里？建议再次进入 IB 并清除该标签的约束。
they have no common ancestor 这就是答案

标签： ios objective-c swift xcode constraints

【解决方案1】：

由于我的代表率低，无法发表评论。您是否已将所有这些视图作为子视图添加到您的主视图中？

我使用的是完全相同的扩展程序，昨天遇到了同样的问题。我通过浏览我的代码并在设置任何约束之前添加所有视图来解决它。明显的错误，但很容易在仓促中犯。

【讨论】：