ios自动布局如何正确编写nslayoutconstraint？

Question

例如，我知道如何使用界面生成器来自动布局按钮。

但是当我尝试使用 nslayoutconstraint 时，

    [self.view addConstraint:[NSLayoutConstraint constraintWithItem:self.thing1 attribute:NSLayoutAttributeLeading relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeLeadingMargin multiplier:1 constant:0]];
    [self.view addConstraint:[NSLayoutConstraint constraintWithItem:self.thing1 attribute:NSLayoutAttributeTop relatedBy:NSLayoutRelationEqual toItem:[self topLayoutGuide] attribute:NSLayoutAttributeBottom multiplier:1 constant:0]];
}

我认为它应该与界面生成器中的约束相同。

但我收到了以下错误消息:

2015-12-10 22:59:01.320 Storyboard[7647:5116727] 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:0x12fd39a60 UIButton:0x12fd3c4f0'thing1'.leading == UIView:0x12fd3d590.leadingMargin>",
    "<NSIBPrototypingLayoutConstraint:0x12fe48040 'IB auto generated at build time for view with fixed frame' H:|-(20)-[UIButton:0x12fd3c4f0'thing1'](LTR)   (Names: '|':UIView:0x12fd3d590 )>"
)

Will attempt to recover by breaking constraint 
<NSLayoutConstraint:0x12fd39a60 UIButton:0x12fd3c4f0'thing1'.leading == UIView:0x12fd3d590.leadingMargin>

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.
2015-12-10 22:59:01.327 Storyboard[7647:5116727] 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. 
(
    "<_UILayoutSupportConstraint:0x12fea5ac0 V:[_UILayoutGuide:0x12fd3d960(0)]>",
    "<_UILayoutSupportConstraint:0x12fe9e960 V:|-(0)-[_UILayoutGuide:0x12fd3d960]   (Names: '|':UIView:0x12fd3d590 )>",
    "<NSLayoutConstraint:0x12fd3d800 V:[_UILayoutGuide:0x12fd3d960]-(0)-[UIButton:0x12fd3c4f0'thing1']>",
    "<NSIBPrototypingLayoutConstraint:0x12fea5e40 'IB auto generated at build time for view with fixed frame' V:|-(20)-[UIButton:0x12fd3c4f0'thing1']   (Names: '|':UIView:0x12fd3d590 )>"
)

Will attempt to recover by breaking constraint 
<NSLayoutConstraint:0x12fd3d800 V:[_UILayoutGuide:0x12fd3d960]-(0)-[UIButton:0x12fd3c4f0'thing1']>

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.

为什么？

Answer 1

在添加任何一组 NSLayoutConstraint 之前，您应该记住将 View 的 translatesAutoresizingMaskIntoConstraints 设置为 NO 或 false。
我已经有一段时间没有使用 Objective-C 了，但如果我没记错的话，你可以这样写:

[self.thing1 setTranslatesAutoresizingMaskIntoConstraints: NO]

或者在 Swift 2 中:

self.thing1.translatesAutoresizingMaskIntoConstraints = false

此外，您必须始终记住在添加任何约束之前将 self.thing1 添加到 self.view。