属性，索引器或动态成员访问不能作为out或ref参数传递[重复]

This question already has an answer here:

这个问题在这里已有答案:

C# property and ref parameter, why no sugar? 9 answers

C#属性和ref参数,为什么没糖? 9个答案

A property or indexer may not be passed as an out or ref parameter 6 answers

属性或索引器可能不会作为out或ref参数6回答传递

Hello I'm having trouble figuring this out. I have these structs and classes.

你好,我很难搞清楚这一点。我有这些结构和类。

struct Circle
{ ... }

class Painting
{
     List<Circle> circles;

     public List<Circle> circles
     {
          get { return circles; }
     }
}

I am trying to modify one of the circles inside the painting class from outside it, using this code:

我试图使用以下代码从外部修改绘画类中的一个圆圈:

MutatePosition(ref painting.Circles[mutationIndex], painting.Width, painting.Height);

This line is giving me a compiler error:

这行给了我一个编译器错误:

A property, indexer or dynamic member access may not be passed as an out or ref parameter

属性,索引器或动态成员访问不能作为out或ref参数传递

Why is this, and what can I do to solve it without changing my code too much?

为什么这样,如果不过多地改变我的代码,我该怎么做才能解决它?

2 个解决方案

#1

The error is pretty clear - you can't pass a property to a ref parameter of a method.

错误很明显 - 您无法将属性传递给方法的ref参数。

You need to make a temporary:

你需要做一个临时的:

var circle = painting.Circles[mutationIndex];
MutatePosition(ref circle, painting.Width, painting.Height);
painting.Circles[mutationIndex] = circle;

That being said, mutable structs are often a bad idea. You might want to consider making this a class instead of a struct.

话虽如此,可变结构往往是一个坏主意。您可能想要考虑将其设为类而不是结构。

#2

If there's only one ref param and no return type for MutatePosition you can return the value.

如果MutatePosition只有一个ref参数且没有返回类型,则可以返回该值。

painting.Circles[mutationIndex] = MutatePosition(circle, painting.Width, painting.Height);

If there are multiple ref params and/or already a return type you can create a new type that includes everything that needs to be returned.

如果有多个ref参数和/或已经是返回类型,则可以创建一个包含需要返回的所有内容的新类型。

class MutateResults() { Circle Circle; object OtherReffedStuff; }

#1