有没有一种方法，以使传递给Control.BeginInvoke委托的类型推断？ [英] Is there a way to cause type inference of the delegate passed to Control.BeginInvoke?

问题描述

Control.BeginInvoke ：

在这两种情况下，它似乎很清楚，编译器都需要推断委托类型的信息。然而，在两种情况下没有的类型推断似乎工作：

In both cases, it seems clear that the compiler has all the information it needs to infer the delegate type. Yet in neither case does the type inference seem to work:

 BeginInvoke(myMethodThatTakesNoParams);

产生编译器错误

produces the compiler error

错误105的最佳重载方法匹配   System.Windows.Forms.Control.BeginInvoke（System.Delegate）有一定的   无效的参数

Error 105 The best overloaded method match for 'System.Windows.Forms.Control.BeginInvoke(System.Delegate)' has some invalid arguments

一样

BeginInvoke(ShowProcessErrors, new object[] { process });

这两种方法调用只编译如果我改变他们explitly创建一个委托并传递。下面的两个编译罚款：

Both method calls only compile if I change them to explitly create a delegate and pass that. Both of the following compile fine:

BeginInvoke(new MethodInvoker(myMethodThatTakesNoParams));

和

BeginInvoke(new ProcessErrorDelegate(ShowProcessErrors), new object[] { process });

似乎有不被任何明显的理由类型推断不会在这里工作。有没有一种方法来调用的BeginInvoke 没有显式地创建一个代表？

There doesn't seem to be any obvious reason why type inference won't work here. Is there a way to call BeginInvoke without explicitly creating a delegate?

推荐答案

问题是， myMethodThatTakesNoParams 是不是一个真正的委托，但所谓的法团由编译器。方法组是不是一个真正的类型在CLR。必须将其转换委托型被使用。当您使用方法组这样的：

The issue is that myMethodThatTakesNoParams isn't really a delegate but a so-called "method group" by the compiler. A method group isn't a real type in the CLR. It must be converted to delegate type to be used. When you use a method group like this:

Action a = myMethodThatTakesNoParams;

编译器可以识别您要的方法组转换为委托并插入转换为您服务。它产生白细胞介素，有效地说道：

The compiler recognizes that you want to convert the method group to a delegate and inserts the conversion for you. It produces IL that effectively says:

Action a = new Action(myMethodThatTakesNoParams);

当你说：

Delegate d = myMethodThatTakesNoParams

编译器并不真正知道该怎么办。它理论上可以挑选任何兼容的委托类型你，但C＃，一般情况下不会插入你没有使用到EX pressions类型。因为它不知道你想要的方法组转换为何种委托，编译器会产生错误。

The compiler doesn't really know what to do. It could theoretically pick any compatible delegate type for you, but C#, in general, does not insert types you did not use into expressions. Since it does not know what delegate you want the method group converted to, the compiler produces an error.

我用变量赋值在我的例子，但同样的逻辑也适用于方法的参数。

I used variable assignment in my examples, but the same logic applies for parameters to methods.

一个变通办法是写有一个特定的委托类型在它自己的扩展方法：

A work around would be to write your own extension method that has a specific delegate type in it:

static class ControlExtensions
{
    public static IAsyncResult BeginInvoke(this Control c, Action a)
    {
        return c.BeginInvoke(a);
    }
}

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