为什么能代表可以互换使用类方法和静态函数？ [英] Why can delegates can be used interchangeably for Class methods and Static functions?

问题描述

我已经使用了代表多年，并没有真正给他们多想。
，但我最近通过假设代表引用一个类的方法时，包括了在签名本引用了我的脸鸡蛋。
下面的例子说明了我的理解的差距。

I've been using delegates for many years, and haven't really given them much thought. But I recently got egg on my face by assuming that delegates included a this reference in the signature when referencing a class method. The below example illustrates the gap in my understanding.

public class SomeClass
{
    public SomeClass(int someProperty)
    {
        SomeProperty = someProperty;
    }

    public int SomeProperty
    { 
        get; 
        set; 
    }

    // Throw in a Member field into the mix
    public int ClassAdd(int x, int y)
    {
        return x + y + SomeProperty;
    }
}

public static class SomeStaticClass
{
    public static int StaticAdd(int x, int y)
    {
        return x + y;
    }
}

为什么我可以添加静态和实例？用户

Why is it that I can add both static and instance subscribers?

    delegate int addDelegate(int x, int y);

    class TestClass
    {
        delegate int addDelegate(int x, int y);

        private void useDelegates()
        {
            addDelegate algorithm;
            algorithm = SomeStaticClass.StaticAdd;
            algorithm += new SomeClass(3).ClassAdd;

            int answer = algorithm(5, 10);
        }
    }

什么是的实际去上？ ;）

推荐答案

如果你创建一个委托指的是一个实例方法，它会捕捉这个（或相关参考）领域来头的 目标 委托的财产。如果你创建一个委托指的是一个静态方法，在目标将是空的。从逻辑上没有必要有，如果您使用的是静态方法的一个实例。

If you create a delegate referring to an instance method, it will capture this (or the relevant reference) in the field backing the Target property of the delegate. If you create a delegate referring to a static method, the Target will be null. Logically there's no need to have an instance if you're using a static method.

作为一个附加的并发症，可以拍摄的扩展的方法如如果他们在扩展类型实例方法：

As one added complications, you can capture extension methods as if they were instance methods on the extended type:

static class Extensions
{
    public static void Foo(this string x)
    {
        Console.WriteLine("Calling Foo on " + x);
    }
}

class Test
{
    static void Main()
    {
        Action action = "text".Foo;
        Console.WriteLine(action.Target); // Prints "text"
    }
}

至于为什么的你可以做到这一切：因为它是有用的，而且也没有理由的不的让你做到这一点：）

As for why you can do all of this: because it's useful, and there's no reason not to allow you to do it :)

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