在代码中设置边距属性 [英] Setting Margin Properties in code

问题描述

  MyControl.Margin.Left = 10; 
  

错误：

无法修改的'System.Windows.FrameworkElement.Margin'的返回值，因为它不是一个变量

解决方案

的问题是， 保证金 是一个属性，它的类型（ 厚度 ）是值类型。当你访问你得到的复制的值回的财产的手段。

即使你的可以改变 Thickness.Left 属性特定值（GRR ...可变的值类型应该不存在），也不会改变保证金。

相反，你需要在保证金属性设置为一个新值。例如（巧合的是马克写了相同的代码）：

 厚度保证金= MyControl.Margin; 
 margin.Left = 10; 
 MyControl.Margin =保证金; 
  

对于库设计一张纸条，我会大大如果厚度更喜欢它是一成不变的，而是与返回一个新的值是原件及复印件，但有一个部分替代方法。然后，你可以写：

  MyControl.Margin = MyControl.Margin.WithLeft（10）; 
  

没有担心可变的值类型，好看可读的古怪行为，都是一个表情...

MyControl.Margin.Left = 10;

Error:

Cannot modify the return value of 'System.Windows.FrameworkElement.Margin' because it is not a variable

解决方案

The problem is that Margin is a property, and its type (Thickness) is a value type. That means when you access the property you're getting a copy of the value back.

Even though you can change the value of the Thickness.Left property for a particular value (grr... mutable value types shouldn't exist), it wouldn't change the margin.

Instead, you'll need to set the Margin property to a new value. For instance (coincidentally the same code as Marc wrote):

Thickness margin = MyControl.Margin;
margin.Left = 10;
MyControl.Margin = margin;

As a note for library design, I would have vastly preferred it if Thickness were immutable, but with methods that returned a new value which was a copy of the original, but with one part replaced. Then you could write:

MyControl.Margin = MyControl.Margin.WithLeft(10);

No worrying about odd behaviour of mutable value types, nice and readable, all one expression...

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