Swift-约束-动态标签宽度

Question

我在一个“行”中有三个按钮。

A-B --- C

我以编程方式添加了以下约束：

A有限制条件：

leading to superview (value = 16)
width (value = 49)
height (value = 40)
trailing to B (value = 16)
top to top layout guide (value = 16)

B有约束条件：

width (value = 49)
height (value = 40)
top to top layout guide (value = 16)

C有约束：

trailing to superview (value = 16)
height (value = 40)
top to top layout guide (value = 16)
leading to B (value >= 20)

现在leading to B如果我运行应用程序并抱怨“无法同时满足约束条件”，则导致C中的leading to B导致错误。

我认为这是由于“缺少” C标签的内容（稍后在运行时添加）导致的，因此宽度未知。

我尝试手动添加C：

width (value = 20) 

“错误”仍然存在，但这应满足导致B> = 20的条件。

However, If I run app, even though the error is printed, the UI looks correct. What is the problem / solution for this?

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. 
    (Note: If you're seeing NSAutoresizingMaskLayoutConstraints that you don't understand, refer to the documentation for the UIView property translatesAutoresizingMaskIntoConstraints) 
(
    "<NSAutoresizingMaskLayoutConstraint:0x1c4098ab0 h=--& v=--& UIView:topView.width == 0   (active)>",
    "<NSLayoutConstraint:0x1c4092480 H:[UIView:parentParent]-(0)-|   (active, names: '|':UIView:topView )>",
    "<NSLayoutConstraint:0x1c40924d0 UIVIew:topView.leading == UIView:parentParent.leading   (active)>",
    "<NSLayoutConstraint:0x1c0094140 H:|-(0)-[UIView:parent](LTR)   (active, names: '|':UIView:parentParent )>",
    "<NSLayoutConstraint:0x1c00940a0 UIView:parent.right == UIView:parentParent.right   (active)>",
    "<NSLayoutConstraint:0x1c0094000 H:|-(16)-[UIButton:A]   (active, names: '|':UIView:parent )>",
    "<NSLayoutConstraint:0x1c0093f60 UIButton:A.trailing == UIButton:B.leading - 16   (active)>",
    "<NSLayoutConstraint:0x1c0094730 H:[UIButton:B]-(>=20)-[UIButton:C]   (active)>",
    "<NSLayoutConstraint:0x1c0094780 UIButton:C.trailing == UIView:parent.trailing - 16   (active)>"
)

Will attempt to recover by breaking constraint 
<NSLayoutConstraint:0x1c0094730 H:[UIButton:B]-(>=20)-[UIButton:C]   (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.

其中A，B，C是按钮， parent是其父视图。 整个父视图在parentParent内部，所有视图都在top视图中。

Answer 1

您的视图已将自动调整大小的蒙版转换为约束，请尝试将其删除：

button.translatesAutoresizingMaskIntoConstraints = false

Answer 2

我已经测试了您的约束条件，但没有看到错误。

不幸的是，运行时的控制台日志不是很有趣，如果您使用Xcode> = 7，则可以为约束设置标识符，选择标识符并转到“属性检查器”，如下图所示：

在此之后，您的日志更具可读性。

如果遇到问题，可以编辑带有完整错误日志的帖子。

编辑：

父视图会出现问题。

在此图像中，您可以看到我的测试（日志中没有错误），我仅将高度约束添加到parent和parentParent中，您可以检查差异。