总是遇到FoodTracker教程;执行此步骤：“实现自定义控件”
当执行第一个检查点时，模拟器会显示一个红色矩形，而不是教程中指示的方形;在我得到的调试窗格上：
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.
我认为在编程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提示都是值得欢迎的。
请注意，我正在构建一个自定义控件...我发现谷歌搜索的所有笔记似乎都不适用。
忽略我的前两个评论......
在该教程中，您将自定义ratingControl添加为垂直堆栈视图的排列子视图。这就是为什么不需要约束的原因。
关键是使类@IBDesignable - 允许Interface Builder和Auto-Layout引擎使用类的内在大小来正确地调整大小/位置/显示它。
（有点令人惊讶的是，它没有在教程中注明。）
这个问题自己消失了。
继续练习，Xcode IDE强调了视图设计中的一些关键点，我被邀请“点击图标”进行修复;其中一个问题与冲突的约束有关。
正如#DonMag所建议的那样，必须将RatingControl类标记为@IBDesignable（稍后将在练习中添加此装饰器）以使Xcode立即查看自定义控件的最终结果。几乎：星星没有出现，控制不会自动缩放添加星星到控制属性。直到我关闭，再次打开并重建整个项目几次。
教程（为Swift 3.2编写）和实际Xcode（在Swift 4中打开的默认项目）的差异适用。
我的想法是，Apple必须更新它自己的在线文档，以避免人们放松心情，试图弄清楚为什么事情不会像预期的那样发挥作用。