需要有关自动布局锚点的帮助

Question

我正在学习自动布局锚点并试图以编程方式实现这个简单的事情

这是我的代码

override func viewWillAppear(_ animated: Bool) {
    super.viewWillAppear(true)

    let view1 = UIView()
    view1.backgroundColor = .brown
    blueView.addSubview(view1)

    view1.translatesAutoresizingMaskIntoConstraints = false
    view1.topAnchor.constraint(equalTo: blueView.topAnchor, constant:10).isActive = true
    view1.bottomAnchor.constraint(equalTo: blueView.bottomAnchor, constant:10).isActive = true
    view1.leadingAnchor.constraint(equalTo: blueView.leadingAnchor, constant:10).isActive = true
    view1.trailingAnchor.constraint(equalTo: blueView.trailingAnchor, constant:10).isActive = true
    view1.heightAnchor.constraint(equalToConstant: 80).isActive = true
    view1.widthAnchor.constraint(equalToConstant: 80).isActive = true
}

这就是我得到的

出了什么问题？

Answer 1

  

出了什么问题？

我看到三类问题：

1. 某些约束不活跃。尚未设置heightAnchor和widthAnchor约束，以便isActive = true
2. 约束是冲突的。您正在基于常量设置约束，而不考虑超视图的尺寸。这导致约束发生冲突，例如，view1不能超过100分和从superview 和底部锚点> 284点，同时全部。
3. 基于常量的约束通常无法将视图置于屏幕中心，因为屏幕大小差异很大。

以下是这三个问题的一种可能解决方案：

override func viewWillAppear(_ animated: Bool) {
    super.viewWillAppear(true)

    let view1 = UIView()
    view1.backgroundColor = .brown
    view.addSubview(view1)

    view1.translatesAutoresizingMaskIntoConstraints = false
    view1.centerXAnchor.constraint(equalTo: view.centerXAnchor).isActive = true
    view1.centerYAnchor.constraint(equalTo: view.centerYAnchor).isActive = true
    view1.heightAnchor.constraint(equalToConstant: 100.0).isActive = true
    view1.widthAnchor.constraint(equalToConstant: 100.0).isActive = true
}

这里，我们将view1的X和Y中心设置为等于超视图的X和Y中心，将view1的高度和宽度定义为常量，并设置所有相关约束活跃。

您可以在Auto Layout Guide中找到其他解决方案。

Answer 2

尝试这样做：

override func viewWillAppear(_ animated: Bool) {
super.viewWillAppear(true)

let view1 = UIView()
view1.backgroundColor = .brown
view.addSubview(view1)

view1.translatesAutoresizingMaskIntoConstraints = false

//Constraints
let centerXConstraint = view1.centerXAnchor.constraint(equalTo: self.view.centerXAnchor, constant: 0)
let centerYConstraint = view1.centerYAnchor.constraint(equalTo: self.view.centerYAnchor, constant: 0)
let widthConstraint = view1.widthAnchor.constraint(equalToConstant: 100)
let heightConstraint = view1.heightAnchor.constraint(equalToConstant: 100)

//Apply constraints
constraintToApply.append(centerXConstraint)
constraintToApply.append(centerYConstraint)
constraintToApply.append(widthConstraint)
constraintToApply.append(heightConstraint) 
}

并添加以下代码：

override func viewDidAppear(_ animated: Bool) {

    // Apply Constraints
    NSLayoutConstraint.activate(constraintToApply)
    self.view.layoutIfNeeded()
}

希望这可以帮到你。

Answer 3

您为每个约束添加+10点。

view1.topAnchor.constraint(equalTo: blueView.topAnchor, constant:10).isActive = true

这意味着＆＃34;将view1的顶部锚点设置为blueView的顶部锚点加上10＆＃34;

只需删除constant:10

即可

view1.topAnchor.constraint(equalTo: blueView.topAnchor).isActive = true

如果您设置了顶部，底部，左侧，前导和尾随锚，您不应设置高度和宽度。宽度和高度将根据这4个锚点计算。所以，你应该删除

view1.heightAnchor.constraint(equalToConstant: 80).isActive = true
view1.widthAnchor.constraint(equalToConstant: 80).isActive = true