以编程方式使用自动布局约束

问题描述：

我正在尝试以编程方式在我的iOS应用中使用autolayout。
我有一个简单的视图控制器，带有这个初始化代码

I'm trying to use autolayout in my iOS app programmatically. I have a simple view controller with this init code

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时，我收到了这个错误：

But when I'm trying to run this, I'm getting this error:

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)]| 
          ^'

它出了什么问题？

当我尝试删除 constraintsWithVisualFormat 中的管道时，我收到此警告：

And when I'm trying to remove pipes in constraintsWithVisualFormat, I'm getting this warning:

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.

由于此原因，我的约束根本没有效果。
我做错了什么？

And as result of this, my constraints have no effect at all. What am I doing wrong?

答

你有三个问题：

首先，您需要在您的按钮子视图上选择基于布局的约束

First, you need to opt-in to layout based contraints on your both your button subviews

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

这将消除NSAutoresizingMaskLayoutConstraint错误。现在，您可以了解布局约束的内容。

This will get rid of the NSAutoresizingMaskLayoutConstraint errors. Now you can get onto what's going on with your layout constraints.

其次，在添加之前，您必须 addSubview 限制。在button1和button2是innerview的子视图之前，你在innerView上调用 addContraints 。

Second, you have to addSubview before adding the constraints. You are calling addContraints on innerView before button1 and button2 are subviews of innerview.

第三，您应指定（尽管文档表明它是可选的）布局字符串是纵向还是水平。 @ H：| [按钮1] [BUTTON2（==按钮1）] |。您还需要一个垂直约束，如 @V：[button1] |，这会将button1与 innerview $ c $的底部对齐c>因为你在按钮上有对齐的基线，按钮2将会跟随。

Third, you should specify (although the docs indicate it is optional) whether the layout string is vertical or horizontal. @"H:|[button1][button2(==button1)]|". You will also want a vertical constraint like @"V:[button1]|" which would align button1 to the bottom of innerview and because you have aligned baselines on the buttons, button2 will follow.

以编程方式使用自动布局约束

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