带有锚点的自动布局边距答案

【问题标题】：Auto-layout margins with anchors带有锚点的自动布局边距
【发布时间】：2017-03-18 07:28:31
【问题描述】：

那么，我认为以下是等价的？

# This is how I usually do
contentView.leftAnchor.constraint(equalTo: leftAnchor, constant: 5).isActive = true
contentView.topAnchor.constraint(equalTo: topAnchor, constant: 5).isActive = true
contentView.rightAnchor.constraint(equalTo: rightAnchor, constant: -5).isActive = true
contentView.bottomAnchor.constraint(equalTo: bottomAnchor, constant: -5).isActive = true

# This is what I tried. I expected the same result..
layoutMargins = UIEdgeInsets(top: 5, left: 5, bottom: 5, right: 5)
contentView.leftAnchor.constraint(equalTo: layoutMarginsGuide.leftAnchor).isActive = true
contentView.topAnchor.constraint(equalTo: layoutMarginsGuide.topAnchor).isActive = true
contentView.rightAnchor.constraint(equalTo: layoutMarginsGuide.rightAnchor).isActive = true
contentView.bottomAnchor.constraint(equalTo: layoutMarginsGuide.bottomAnchor).isActive = true

虽然我似乎错了。如何使用边距、约束和锚点获得 containerView 和父级之间的 5 边距？

【问题讨论】：

标签： ios cocoa-touch autolayout nslayoutconstraint

【解决方案1】：

目标-C：

[contentView.leftAnchor constraintEqualToAnchor:contentView.superview.leftAnchor constant:5].active = YES;
[contentView.rightAnchor constraintEqualToAnchor:contentView.superview.rightAnchor constant:5].active = YES;
[contentView.topAnchor constraintEqualToAnchor:contentView.superview.topAnchor constant:5].active = YES;
[contentView.bottomAnchor constraintEqualToAnchor:contentView.superview.bottomAnchor constant:5].active = YES;

斯威夫特 3：

contentView.leftAnchor.constraint(equalTo: contentView.superview?.leftAnchor, constant: 5).isActive = true
contentView.rightAnchor.constraint(equalTo: contentView.superview?.rightAnchor, constant: 5).isActive = true
contentView.topAnchor.constraint(equalTo: contentView.superview?.topAnchor, constant: 5).isActive = true
contentView.bottomAnchor.constraint(equalTo: contentView.superview?.bottomAnchor, constant: 5).isActive = true

【讨论】：

如果你阅读了这个问题，你会发现这正是你所说的我现在正在做的事情，我想知道如何让它与 layoutMarginGuides 一起工作

【解决方案2】：

我通过阅读这个问题找到了解决方案：Auto Layout: layoutMarginsGuide。

从init 设置layoutMargins 时似乎存在问题。

不过，我没有将layoutMargins 设置为viewDidMoveToSuperView，而是将其设置为updateConstraints，这也可以正常工作。

所以现在的代码是：

override init(frame: CGRect) {
    super.init(frame: frame)
    contentView.leftAnchor.constraint(equalTo: layoutMarginsGuide.leftAnchor).isActive = true
    contentView.topAnchor.constraint(equalTo: layoutMarginsGuide.topAnchor).isActive = true
    contentView.rightAnchor.constraint(equalTo: layoutMarginsGuide.rightAnchor).isActive = true
    contentView.bottomAnchor.constraint(equalTo: layoutMarginsGuide.bottomAnchor).isActive = true
}

override func updateConstraints() {
    super.updateConstraints()
    layoutMargins = UIEdgeInsets(top: 5, left: 5, bottom: 5, right: 5)
}

然后具有与以下相同的效果：

contentView.leftAnchor.constraint(equalTo: leftAnchor, constant: 5).isActive = true
contentView.topAnchor.constraint(equalTo: topAnchor, constant: 5).isActive = true
contentView.rightAnchor.constraint(equalTo: rightAnchor, constant: -5).isActive = true
contentView.bottomAnchor.constraint(equalTo: bottomAnchor, constant: -5).isActive = true

【讨论】：

不确定在这种情况下是否重要，但一般情况下，应该在实现结束时调用super.updateConstraints()：Apple Documentation

【解决方案3】：

似乎在updateConstraints() 中设置layoutMargins 有效，但有以下警告：

override func updateConstraints() {
    super.updateConstraints()
    layoutMargins = UIEdgeInsets(top: 8, left: 8, bottom: 8, right: 8)
}

上述代码将无法更新边距，因为新值与系统默认值相同。所以为了安全起见，首先将边距重置为零：

override func updateConstraints() {
    super.updateConstraints()
    layoutMargins = .zero
    layoutMargins = UIEdgeInsets(top: 8, left: 8, bottom: 8, right: 8)
}

此外，如果您的目标是将初始边距设置为 .zero，最好先将它们设置为非零值，以确保通知视图更改。

【讨论】：