我有以下代码适用于高度和宽度约束。尝试添加前导约束和上限约束时会崩溃。我还有其他具有高度,宽度,前导和顶部约束的按钮集,但是它们都设置在情节提要板上,因此我认为这些是我必须添加到每个按钮的唯一4个约束。
我有7个按钮,每个按钮一天。当我添加代码来执行前导约束和顶部约束时,它会与以下错误代码一起破坏。高度/宽度都可以正常工作。我猜想这与我向视图控制器添加子视图或按钮关系的方式有关,或者以编程方式进行时,我需要的不止是我一直在使用的4个约束(前导,顶部,宽度,高度)在情节提要上。
func setupWeekdayButtons() {
self.weeklyButtons = [self.mondayButton, self.tuesdayButton, self.wednesdayButton, self.thursdayButton, self.fridayButton, self.saturdayButton, self.sundayButton]
for i in 0...6 {
print(i)
self.weeklyButtons[i].translatesAutoresizingMaskIntoConstraints = false
self.weeklyButtons[i].setTitle(self.weekdayLabels[i], for: .normal)
self.weeklyButtons[i].layer.borderColor = UIColor.black.cgColor
self.weeklyButtons[i].titleLabel?.textAlignment = .center
self.weeklyButtons[i].layer.borderWidth = 1.0
self.weeklyButtons[i].layer.cornerRadius = 6.0
self.weeklyButtons[i].setTitleColor(.black, for: .normal)
self.weeklyButtons[i].setTitleColor(.red, for: .selected)
self.weeklyButtons[i].addTarget(self, action: #selector(selectedDailyButton), for: .touchUpInside)
self.view.addSubview(self.weeklyButtons[i])
let heightConstraint = NSLayoutConstraint(
item: self.weeklyButtons[i],
attribute: NSLayoutConstraint.Attribute.height,
relatedBy: NSLayoutConstraint.Relation.equal,
toItem: nil,
attribute: NSLayoutConstraint.Attribute.notAnAttribute,
multiplier: 1.0,
constant: 30
)
let widthConstraint = NSLayoutConstraint(
item: self.weeklyButtons[i],
attribute: NSLayoutConstraint.Attribute.width,
relatedBy: NSLayoutConstraint.Relation.equal,
toItem: nil,
attribute: NSLayoutConstraint.Attribute.notAnAttribute,
multiplier: 1.0,
constant: 30
)
let leadingConstraint = NSLayoutConstraint(
item: self.weeklyButtons[i],
attribute: NSLayoutConstraint.Attribute.leading,
relatedBy: NSLayoutConstraint.Relation.equal,
toItem: self.view,
attribute: NSLayoutConstraint.Attribute.leading,
multiplier: 1.0,
constant: 100
)
let topConstraint = NSLayoutConstraint(
item: self.weeklyButtons[i],
attribute: NSLayoutConstraint.Attribute.top,
relatedBy: NSLayoutConstraint.Relation.equal,
toItem: self.view,
attribute: NSLayoutConstraint.Attribute.top,
multiplier: 1.0,
constant: 100
)
self.weeklyButtons[i].addConstraint(heightConstraint)
self.weeklyButtons[i].addConstraint(widthConstraint)
self.weeklyButtons[i].addConstraint(leadingConstraint)
self.weeklyButtons[i].addConstraint(topConstraint)
}
}
2019-03-07 14:38:59.176638-0500
每日[27852:1408014] [LayoutConstraints]没有为约束准备视图层次结构:
当添加到视图时,约束的项必须是该视图的后代(或视图本身)。如果在组装视图层次结构之前需要解决约束,则会崩溃。中断-[UIView(UIConstraintBasedLayout)_viewHierarchyUnpreparedForConstraint:]进行调试。
2019-03-07 14:38:59.177816-0500每日[27852:1408014] [LayoutConstraints]视图层次结构未准备好进行约束。
约束:
容器层次结构:
>
| >
在容器层次结构中找不到视图:>
该视图的超级视图:没有超级视图
2019-03-07 14:38:59.192176-0500 Daily [27852:1408014] ***由于未捕获的异常'NSGenericException'而终止应用程序,原因:'无法在视图上安装约束。约束是否引用了视图子树之外的内容?那是非法的。约束:视图:>
最佳答案
self.weeklyButtons[i].addConstraint(leadingConstraint)
约束涉及
weeklyButtons[i]
和self.view
。如果使用addConstraint
激活约束,则必须将约束添加到两个视图的公共祖先中。这就是此错误消息告诉您的内容:当添加到视图时,约束的项必须是该视图的后代(或视图本身)。
由于
self.view
是weeklyButtons[i]
的超级视图,因此它被视为两个视图的共同祖先。因此,在这种情况下,您可以将约束添加到self.view
:self.view.addConstraint(leadingConstraint)
但是不要那样做。从iOS 8开始,您可以直接激活约束,UIKit会自动将其添加到正确的视图中:
leadingConstraint.isActive = true
但是不要那样做。由于您要连续添加四个约束,因此像这样一次激活四个约束可能会稍微更有效:
NSLayoutConstraint.activate([
leadingConstraint,
topConstraint,
widthConstraint,
heightConstraint])
但是不要那样做。从iOS 9开始,创建约束的方式更具可读性:
NSLayoutConstraint.activate([
self.weeklyButtons[i].heightAnchor.constraint(equalToConstant: 30),
self.weeklyButtons[i].widthAnchor.constraint(equalToConstant: 30),
self.weeklyButtons[i].leadingAnchor.constraint(equalTo: view.leadingAnchor, constant: 100),
self.weeklyButtons[i].topAnchor.constraint(equalTo: view.topAnchor, constant: 100),
])
但是不要那样做。使用
for
/ in
循环而不是索引变量i
:func setupWeekdayButtons() {
weeklyButtons = [mondayButton, tuesdayButton, wednesdayButton, thursdayButton, fridayButton, saturdayButton, sundayButton]
for (button, title) in zip(weeklyButtons, weekdayLabels) {
button.translatesAutoresizingMaskIntoConstraints = false
button.setTitle(title, for: .normal)
button.layer.borderColor = UIColor.black.cgColor
button.titleLabel?.textAlignment = .center
button.layer.borderWidth = 1.0
button.layer.cornerRadius = 6.0
button.setTitleColor(.black, for: .normal)
button.setTitleColor(.red, for: .selected)
button.addTarget(self, action: #selector(selectedDailyButton), for: .touchUpInside)
view.addSubview(button)
NSLayoutConstraint.activate([
button.heightAnchor.constraint(equalToConstant: 30),
button.widthAnchor.constraint(equalToConstant: 30),
button.leadingAnchor.constraint(equalTo: view.leadingAnchor, constant: 100),
button.topAnchor.constraint(equalTo: view.topAnchor, constant: 100),
])
}
}
去做。
关于ios - 以编程方式添加领先/顶级约束,我们在Stack Overflow上找到一个类似的问题:https://stackoverflow.com/questions/55051717/