iOS 11：“无法同时满足约束”
始终运行FoodTracker教程；遵循以下步骤：“实现自定义控件”
编号/doc/uid/SW1 40015214-CH19-SW1
在执行第一个检查点时，模拟器显示一个红色的矩形，而不是教程中指示的正方形；在调试窗格中，我得到：
2018-02-09 11:19:42.130595+0100 FoodTracker[7439:80369] [MC] Lazy loading NSBundle MobileCoreServices.framework
2018-02-09 11:19:42.131628+0100 FoodTracker[7439:80369] [MC] Loaded MobileCoreServices.framework
2018-02-09 11:19:42.165143+0100 FoodTracker[7439:80369] [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:0x60400028a3c0 UIButton:0x7f8a0bd0e330.width == 44 (active)>",
"<NSLayoutConstraint:0x60400028cda0 'UISV-canvas-connection' FoodTracker.RatingControl:0x7f8a0bd08890.leading == UIButton:0x7f8a0bd0e330.leading (active)>",
"<NSLayoutConstraint:0x60400028ce40 'UISV-canvas-connection' H:[UIButton:0x7f8a0bd0e330]-(0)-| (active, names: '|':FoodTracker.RatingControl:0x7f8a0bd08890 )>",
"<NSLayoutConstraint:0x60400028c940 'UIView-Encapsulated-Layout-Width' FoodTracker.RatingControl:0x7f8a0bd08890.width == 200 (active)>"
)
Will attempt to recover by breaking constraint
<NSLayoutConstraint:0x60400028a3c0 UIButton:0x7f8a0bd0e330.width == 44 (active)>
Make a symbolic breakpoint at UIViewAlertForUnsatisfiableConstraints to catch this in the debugger.
The methods in the UIConstraintBasedLayoutDebugging category on UIView listed in <UIKit/UIView.h> may also be helpful.
2018-02-09 11:19:42.165949+0100 FoodTracker[7439:80369] [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:0x60400028a370 UIButton:0x7f8a0bd0e330.height == 44 (active)>",
"<NSLayoutConstraint:0x60400028a320 'UISV-canvas-connection' FoodTracker.RatingControl:0x7f8a0bd08890.top == UIButton:0x7f8a0bd0e330.top (active)>",
"<NSLayoutConstraint:0x60400028cf30 'UISV-canvas-connection' V:[UIButton:0x7f8a0bd0e330]-(0)-| (active, names: '|':FoodTracker.RatingControl:0x7f8a0bd08890 )>",
"<NSLayoutConstraint:0x60400028c990 'UIView-Encapsulated-Layout-Height' FoodTracker.RatingControl:0x7f8a0bd08890.height == 110 (active)>"
)
Will attempt to recover by breaking constraint
<NSLayoutConstraint:0x60400028a370 UIButton:0x7f8a0bd0e330.height == 44 (active)>
Make a symbolic breakpoint at UIViewAlertForUnsatisfiableConstraints to catch this in the debugger.
The methods in the UIConstraintBasedLayoutDebugging category on UIView listed in <UIKit/UIView.h> may also be helpful. 我认为在以编程方式创建按钮并在此处应用自定义约束时，会发生一些变化：(我正在使用Swift和Xcode 9)
// Add constraints
button.translatesAutoresizingMaskIntoConstraints = false
button.heightAnchor.constraint(equalToConstant: 44.0).isActive = true
button.widthAnchor.constraint(equalToConstant: 44.0).isActive = true 任何解决这个问题的暗示都是受欢迎的。
请注意我正在建立一个自定义控件..。我在谷歌上发现的所有注释似乎都不适用。
回答 4
Stack Overflow用户
发布于 2018-02-11 14:08:35
结束语
这个问题自己消失了。
从摘录开始，Xcode IDE强调了视图设计中的一些关键点，其中我被邀请“点击图标”来修复；其中一个问题与冲突的对比有关。
正如#DonMag所建议的那样，必须将RatingControl类标记为@IBDesignable (稍后将在摘录时添加这个装饰符)，以便Xcode立即查看自定义控件的最终结果。几乎:星星没有出现，控件也不会自动缩放，将星星添加到控件属性中。直到我关闭，重新打开，并重建了几次整个项目。
不同的教程(为Swift 3.2编写)和实际Xcode (在Swift 4中打开的默认项目适用。
这是我的想法，苹果必须更新它自己的在线文档，以避免人们失去理智，试图找出为什么事情不能像预期的那样工作。
Stack Overflow用户
发布于 2018-02-09 13:50:57
忽略我的前两条评论..。
在该教程中，您将添加自定义ratingControl作为垂直堆栈视图的排列子视图。这就是不需要约束的原因。
关键是使类@IBDesignable -它允许接口生成器和自动布局引擎使用类的内在大小，以适当的大小/位置/显示它。
(只是有点奇怪，这一点在本教程中没有提到。)
Stack Overflow用户
发布于 2020-03-17 06:15:04
我也有过同样的问题。此外，红色方块看起来比教程中显示的要大。为了使红色方块接受44大小的约束，我必须确保RatingControl位于堆栈视图的中，而不是在下面。
我附加图片来澄清我所说的“内部”堆栈视图的含义。
https://stackoverflow.com/questions/48706274
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