ios - 在代码中更改大小类 (Swift)

Question

我一直在尝试使用纯代码(未使用 Storyboard)构建自适应布局。我使用布局 anchor 来设置约束并利用 traitCollectionDidChange 方法在不同的约束集和其他界面更改之间变化。我使用 switch 语句来调用具有相应约束集的相应方法。

override func traitCollectionDidChange(_ previousTraitCollection: UITraitCollection?) {
    super.traitCollectionDidChange(previousTraitCollection)

    switch (traitCollection.horizontalSizeClass, traitCollection.verticalSizeClass) {
    case (.regular, .regular):
        setupRegularRegular()

    case (.compact, .compact):
        setupCompactCompact()

    case (.regular, .compact):
        setupRegularCompact()

    case (.compact, .regular):
        setupCompactRegular()

    default: break
    }

}

为了测试，我只更改了一个约束，即centerYAnchor.constraint。在纵向中，常数是 -150，在横向中，我希望将其更改为 50。对于 iPad，我将常数设置为 0。

bigLabel.centerYAnchor.constraint(equalTo: view.centerYAnchor, constant: -150).isActive = true

在 iPhone 和 iPad 之间切换时工作正常。但是，如果您开始将 iPhone 从纵向旋转到横向，则布局系统会失败，并显示:

[LayoutConstraints] Unable to simultaneously satisfy constraints.
Probably at least one of the constraints in the following list is one you don't want. 
Try this: 
    (1) look at each constraint and try to figure out which you don't expect; 
    (2) find the code that added the unwanted constraint or constraints and fix it. 
(
"<NSLayoutConstraint:0x600000097890 UILabel:0x7fac02c08aa0'Main Label'.centerY == UIView:0x7fac02e0a950.centerY - 150   (active)>",
"<NSLayoutConstraint:0x604000097840 UILabel:0x7fac02c08aa0'Main Label'.centerY == UIView:0x7fac02e0a950.centerY + 50   (active)>"
)

Will attempt to recover by breaking constraint 
<NSLayoutConstraint:0x604000097840 UILabel:0x7fac02c08aa0'Main Label'.centerY == UIView:0x7fac02e0a950.centerY + 50   (active)>

我尝试覆盖各种方法并将约束的 isActive 属性设置为 false，然后再设置回 true，但这没有帮助。我在网上搜索了几天。目前没有解决方案。所以我的问题是，在旋转设备时，你如何以正确的方式在尺寸等级之间切换？是否有必要重写任何其他方法或其他方法？纯代码自适应布局有更好的解决方案吗？关于自适应布局/大小类/布局 anchor 和代码约束(不使用 Storyboard )，是否有任何最佳实践？感谢您的帮助!

附言设置约束的方法是:

func setupCompactRegular() {

    bigLabel.centerYAnchor.constraint(equalTo: view.centerYAnchor, constant: -150).isActive = true

}

func setupRegularCompact() {

    bigLabel.centerYAnchor.constraint(equalTo: view.centerYAnchor, constant: 50).isActive = true

}

Answer 1

问题是你正在创建新的约束..尝试持有对你的约束的引用并改变你的方法来更新它们

func setupCompactRegular() {

    self.bigLabelCenterYAnchor.constant = -150

}

func setupRegularCompact() {

    self.bigLabelCenterYAnchor.constant = 50

}

如果没有自动更新，立即调用 layoutIfNeeded()