我正在尝试从我的 View Controller 设置一个 subview 弹出窗口并使用视觉格式约束来定位项目。我希望 subview 看起来像这样，tableView 的高度为 150 pts，imageView 的高度为 100 pts，titleLabel 的高度为 50 pts 并且位于 imageView 的左下角:

为了尝试实现这一点，我使用了以下代码:

override func didMoveToSuperview() {
    super.didMoveToSuperview()

    // Add views
    addSubview(titleLabel)
    addSubview(tableView)
    addSubview(imageView)

    // Setup constraints
    heightAnchor.constraint(equalToConstant: 250).isActive = true

    var constraints = [NSLayoutConstraint]()
     let views: [String: UIView] = ["imageView": imageView, "titleLabel": titleLabel, "tableView": tableView]
    constraints += NSLayoutConstraint.constraints(withVisualFormat: "H:|[tableView(150)]|", options: [], metrics: nil, views: views)
    constraints += NSLayoutConstraint.constraints(withVisualFormat: "V:|[titleLabel][tableView]|", options: [], metrics: nil, views: views)
    constraints += NSLayoutConstraint.constraints(withVisualFormat: "H:|[titleLabel(20)]|", options: [], metrics: nil, views: views)
    constraints += NSLayoutConstraint.constraints(withVisualFormat: "V:|[imageView(100)][tableView]|", options: [], metrics: nil, views: views)
    constraints += NSLayoutConstraint.constraints(withVisualFormat: "H:|[imageView(100)]|", options: [], metrics: nil, views: views)
    NSLayoutConstraint.activate(constraints)
}

但这会导致以下输出(未显示 titleLabel):

最佳答案

问题不在于您的约束。这与您的观点顺序有关。在 imageView 之后添加 titleLabel 使其显示在 imageView 的顶部:

// Add views
addSubview(tableView)
addSubview(imageView)
addSubview(titleLabel)

由于您的 titleLabel 的位置是相对于您的 imageView 的，我建议将其设为 subview 。以下是我建议的限制条件:

override func didMoveToSuperview() {
    super.didMoveToSuperview()

    // Add views
    addSubview(tableView)
    addSubview(imageView)
    imageView.addSubview(titleLabel)

    // Setup constraints
    heightAnchor.constraint(equalToConstant: 250).isActive = true

    var constraints = [NSLayoutConstraint]()
    let views: [String: UIView] = ["imageView": imageView, "titleLabel": titleLabel, "tableView": tableView]

    // tableView is 150 wide and stuck to both sides of its superView making the superView 150 wide
    constraints += NSLayoutConstraint.constraints(withVisualFormat: "H:|[tableView(150)]|", options: [], metrics: nil, views: views)

    // imageView is 100 tall and stuck to top of superView; tableView takes up the rest
    constraints += NSLayoutConstraint.constraints(withVisualFormat: "V:|[imageView(100)][tableView]|", options: [], metrics: nil, views: views)

    // imageView is as wide as its superView because it is stuck to both sides
    constraints += NSLayoutConstraint.constraints(withVisualFormat: "H:|[imageView]|", options: [], metrics: nil, views: views)

    // titleLabel is 20 tall and stuck to the bottom of its superView (notice only one "|")
    constraints += NSLayoutConstraint.constraints(withVisualFormat: "V:[titleLabel(20)]|", options: [], metrics: nil, views: views)

    // titleLabel is 50 wide and stuck to the left of its superView (again only one "|")
    constraints += NSLayoutConstraint.constraints(withVisualFormat: "H:|[titleLabel(50)]", options: [], metrics: nil, views: views)

    NSLayoutConstraint.activate(constraints)
}

关于ios - Swift:视觉格式语言约束问题，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/41428354/