使用自动布局约束编程(Using autolayout constraints programmat

我想在我的iOS应用程序使用自动布局。我有这个初始化代码一个简单的视图控制器

UIView *innerView = [[UIView alloc] initWithFrame:self.view.bounds];

UIButton *button1 = [UIButton buttonWithType:UIButtonTypeRoundedRect];
[button1 setFrame:CGRectMake(50, 50, 150, 50)];
[button1 setTitle:@"button1" forState:UIControlStateNormal];

UIButton *button2 = [UIButton buttonWithType:UIButtonTypeRoundedRect];
[button2 setFrame:CGRectMake(250, 50, 150, 50)];
[button2 setTitle:@"button2" forState:UIControlStateNormal];

[innerView addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"|[button1][button2(==button1)]|" options:NSLayoutFormatAlignAllBaseline metrics:0 views:NSDictionaryOfVariableBindings(button1, button2)]];

[innerView addSubview:button1];
[innerView addSubview:button2];
[self.view addSubview:innerView];

但是，当我试图运行它，我得到这个错误：

Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: 'Unable to parse constraint format: 
Unable to interpret '|' character, because the related view doesn't have a superview 
|[button1][button2(==button1)]| 
          ^'

它出什么问题了？

当我试图消除管道constraintsWithVisualFormat ，我得到这样的警告：

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:0x716be10 h=--& v=--& UIRoundedRectButton:0x71631f0.midX == + 325>",
    "<NSAutoresizingMaskLayoutConstraint:0x7169940 h=--& v=--& H:[UIRoundedRectButton:0x715fb80(150)]>",
    "<NSAutoresizingMaskLayoutConstraint:0x7169860 h=--& v=--& UIRoundedRectButton:0x715fb80.midX == + 125>",
    "<NSLayoutConstraint:0x7164cd0 UIRoundedRectButton:0x71631f0.width == UIRoundedRectButton:0x715fb80.width>",
    "<NSLayoutConstraint:0x7164940 H:[UIRoundedRectButton:0x715fb80]-(0)-[UIRoundedRectButton:0x71631f0]>"
)

Will attempt to recover by breaking constraint 
<NSLayoutConstraint:0x7164940 H:[UIRoundedRectButton:0x715fb80]-(0)-[UIRoundedRectButton:0x71631f0]>

Break on objc_exception_throw to catch this in the debugger.
The methods in the UIConstraintBasedLayoutDebugging category on UIView listed in <UIKit/UIView.h> may also be helpful.

而作为这样的结果，我的约束没有任何效果可言。我究竟做错了什么？

Answer 1:

你有三个问题：

首先，你需要选择加入到布局上的两个按钮的子视图基于约束上

[button1 setTranslatesAutoresizingMaskIntoConstraints:NO];
[button2 setTranslatesAutoresizingMaskIntoConstraints:NO];

这将摆脱NSAutoresizingMaskLayoutConstraint错误。现在你可以到发生了什么事情与你的布局约束。

其次，你必须addSubview添加约束之前。要调用addContraints之前按钮1和按钮2是innerview的子视图上innerView。

第三，应指定（尽管文件表明它是可选的）布局字符串是否是垂直或水平。 @"H:|[button1][button2(==button1)]|" 。您还需要一个垂直的约束像@"V:[button1]|" 这将对齐Button1以底部innerview因为你已经对准上的按钮基线，BUTTON2将随之而来。

Answer 2:

只是为了记录：关于失踪的上海华异常被已被触发constraintsWithVisualFormat不addConstraints