如何在代码中编辑约束 [英] How to edit constraint in code

问题描述

我有一个以宽度约束为100开头的网页。

当用户点击按钮时，我想将约束更改为：200。 p>

我尝试过：

  NSLayoutConstraint * constrain = [NSLayoutConstraint 
 constraintWithItem：self.webPage 
 attribute：NSLayoutAttributeWidth 
 relatedBy：NSLayoutRelationEqual 
 toItem：self.webPage 
 attribute：NSLayoutAttributeWidth 
 multiplier：1 
常数：100 ]; 
 
 
 
 
 [self.webPage addConstraint：constrain]; 
  

但是这会抛出这个异常：
无法同时满足约束。 p>

任何想法？

解决方案

1. 获取对原始约束的引用，将常量部分更改为200


2. 获取对原始约束的引用并将其从视图中删除，然后添加新约束

我会去第一个选项。要获取引用，请为您的viewController添加一个 @property 约束，并在创建它时分配它。

如果您在xib或故事板中创建约束，将带有IBOutlet连接的约束连接到您的代码，类似于您在连接UILabel时所做的操作。

然后，您可以轻松地调整约束的常量部分。

---

此外，您的约束应该更符合以下条件：

  NSLayoutConstraint * constrain = [NSLayoutConstraint 
 constraintWithItem：self.webPage 
 attribute：NSLayoutAttributeWidth 
 relatedBy：NSLayoutRelationEqual 
 toItem：nil 
 attribute：NSLayoutAttributeNotAnAttribute 
 multiplier：1 
 constant：100]; 
  

I have a web page that start with a width constrain of 100.

When the user click a button i want to change the constrain to : 200.

I tried this:

NSLayoutConstraint *constrain = [NSLayoutConstraint
                                 constraintWithItem:self.webPage
                                 attribute:NSLayoutAttributeWidth
                                 relatedBy:NSLayoutRelationEqual
                                 toItem:self.webPage
                                 attribute:NSLayoutAttributeWidth
                                 multiplier:1
                                 constant:100];




[self.webPage addConstraint:constrain];

But this throws out this exception : "Unable to simultaneously satisfy constraints."

Any ideas?

解决方案

You have two options.

1. Get a reference to the original constraint and change the constant part to 200
2. Get a reference to the original constraint and remove it from the view, and add the new constraint

I would go for the first option. To get a reference add a @property for the constraint to your viewController and assign it when you create it.

If you are creating the constraint in a xib or storyboard connect the constraint with a IBOutlet connection to your code, similar to what you do when you connect a UILabel.

You can then easily adjust the constant part of the constraint.

---

Also you constraint should probably be more along these lines:

NSLayoutConstraint *constrain = [NSLayoutConstraint
                                 constraintWithItem:self.webPage
                                 attribute:NSLayoutAttributeWidth
                                 relatedBy:NSLayoutRelationEqual
                                 toItem:nil
                                 attribute:NSLayoutAttributeNotAnAttribute
                                 multiplier:1
                                 constant:100];

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