如何将Func放入C#属性(注释)中? [英] How do you put a Func in a C# attribute (annotation)?

问题描述

我有一个C#注释:

[AttributeUsage(AttributeTargets.Method)]
public class OperationInfo : System.Attribute {
    public enum VisibilityType {
        GLOBAL,
        LOCAL,
        PRIVATE
    }
    public VisibilityType Visibility { get; set; }
    public string Title { get; set; }
    public Func<List<string>, List<string>> Func;

    public OperationInfo(VisibilityType visibility, string title, Func<List<string>, List<string>> function) {
        Visibility = visibility;
        Title = title;
        Func = function;
    }
}

如您所见，有一个属性是Func，我想动态地调用它.基本上，我想解析所有具有此批注的方法，然后调用绑定到该批注的Func.

As you can see, there is a property which is a Func and I want to call it dynamically. Basically, I'd like to parse all the methods which have this annotation and then call the Func binded to the annotation.

我想这样使用它(这是echo函数的简单示例，它获取一个字符串并返回相同的字符串):

I'd like to use it like this (this is a simple example of an echo function, which gets a string and return the same string):

[OperationInfo(OperationInfo.VisibilityType.GLOBAL, "echo", IDoEcho)]
    public static string DoEcho(string a)
    {
        return a;
    }

    [OperationInfo(OperationInfo.VisibilityType.PRIVATE, null, null)]
    public static List<string> IDoEcho(List<string> param) {
        return new List<string>() { DoEcho(param[0]) };
    }

我的Annotation类没有任何错误，但是当涉及到重新生成整个解决方案时，每次我声明带有注释的方法时，都会出现一个错误，告诉我必须在注释中使用文字.

I've got no error in my Annotation class but when it comes to regenerate the entire solution, each time I declare a method with the annotation I've got an error which tells me that I must use literals in an annotation.

我知道有局限性，但是有什么办法可以避免这个问题?我知道我可以使用字符串代替Func，并动态查找名称与字符串相同的函数，但是我不想这样做.

I understand there is limitations, but is there any way I can avoid this problem? I know I can use a string instead of a Func, and look dynamically for the function whose name is the same as the string, but I would like not to do so.

感谢您的帮助:)

推荐答案

我认为这是不可能的，c#仅允许您仅使用具有常量值的属性.

I don't think it is possible, c# only allows you to use Attributes with constant values only.

执行此操作的一种方法是创建一个类而不是一个func，然后将该类的类型传递给属性. 然后，您需要使用反射实例化它并在其中执行一个方法.

One way of doing this would be to create a class instead of a func, and then you pass the type of that class into the attribute. You'd then need to instantiate it with reflection and execute a method in it.

所以一个例子是:

public interface IDoStuff
{
    IList<string> Execute();
}

然后您的属性将采用类型而不是Func

then your attribute would take a type instead of a Func

public OperationInfo(VisibilityType v, string title, Type type)
{
   ///...
}

然后，您将创建一个实现您的接口的类，并将其传递给属性.尽管这意味着(至少在最初，并且不知道您的问题)，但是每次您想要返回不同的结果时，您都需要创建一个新类.

you then would create a class that implements your interface and pass it into the attribute. Although this would mean that (at least initially, and without knowing your problem) you will need to create a new class every time you want to return different results.

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