问题描述

我正在开发一个 Windows 窗体应用程序，它包含自定义控件以及可以从 UI 线程以外的线程调用的方法.所以这些方法因此看起来有点像这样来防止异常:

I'm working on a Windows Forms application, and it contains custom controls with methods that can potentially be called from threads other than the UI thread. So these methods therefore look a bit like this to prevent exceptions:

public void DoSomeStuff()
{
    if (InvokeRequired)
    {
        Invoke((Action)DoSomeStuff);
    }
    else
    {
        // Actually do some stuff.
    }
}

方法组 DoSomeStuff 到 Action 的显式转换引起了我的注意，因此我对委托和其他相关主题的研究比我以前更深入之前.

The explicit cast of the method group DoSomeStuff to an Action caught my attention, and so I've been looking into delegates and other related subjects more deeply than I have before.

虽然我在这里看到了一些相关的问题，但我一直无法找到我的确切答案，即:

Although I've seen some related questions here, I haven't been able to find exactly the answer to mine, which is:

在这种情况下，为什么方法组 DoSomeStuff 需要显式转换为 Action?

Why does the method group DoSomeStuff require explicit casting to an Action in this case?

如果我删除演员表，则会收到两个错误:

If I remove the cast, then I get two errors:

错误 102 参数 1:无法从方法组"转换为'System.Delegate'

Error 102 Argument 1: cannot convert from 'method group' to 'System.Delegate'

错误 101 的最佳重载方法匹配'System.Windows.Forms.Control.Invoke(System.Delegate，参数object[])' 有一些无效参数

Error 101 The best overloaded method match for 'System.Windows.Forms.Control.Invoke(System.Delegate, params object[])' has some invalid arguments

编译器显然对使用哪个 Invoke 重载感到困惑这一事实似乎是一个很大的提示，但我仍然不确定为什么它无法弄清楚这一点.我希望编译器能够推断出应该使用单个 Delegate 参数的 Invoke 的第一个重载.

The fact that the compiler is apparently confused about which overload of Invoke to use seems like a pretty big hint, but I'm still not sure about why exactly it can't figure that out. I would expect the compiler to deduce that the first overload of Invoke, which takes a single Delegate argument, is the one that should be used.

我希望因为这样写代码没有问题:

I would expect that because there is no problem if the code is written like this:

Action a = DoSomeStuff;
Invoke(a);

方法组 DoSomeStuff 可以隐式转换为 Action 委托类型，并且 Action 派生自(技术上?)System.Delegate，所以 Invoke 可以毫无问题地处理参数 a.但是，当我尝试直接将 DoSomeStuff 作为参数传递时，为什么编译器不能完成隐式转换呢?老实说，我不相信我自己的逻辑，但我仍然不确定我错过了什么.

The method group DoSomeStuff can be implicitly converted to the Action delegate type, and Action derives (technically?) from System.Delegate, so Invoke can handle the argument a without any trouble. But then why can't the implicit conversion be done by the compiler when I try to pass DoSomeStuff as the argument directly? To be honest I'm not convinced by my own logic here, but I still am not sure what I'm missing.

推荐答案

问题不在于编译器无法选择重载.最佳匹配"重载是您想要的重载，但它具有无效参数.C# 语言没有定义任何从方法组 (DoSomeStuff) 到 System.Delegate 的隐式转换.

The problem is not that the compiler has trouble picking an overload. The "best match" overload is the one you want but it has invalid arguments. The C# language does not define any implicit conversion from method group (DoSomeStuff) to System.Delegate.

您可能会说编译器应该只选择一种 Action/Func 类型，而这已作为语言特性被请求.现在这不是 C# 的一部分.(我不知道为什么；我希望语言请求能够通过.)

You might say that the compiler should just pick one of the Action/Func types and this has been requested as a language feature. Right now this is not part of C#. (I don't know why; I hope the language request goes through.)

System.Windows.Forms.Control.Invoke 是在 .NET 1.0 中创建的.今天，人们会使用以下签名:

System.Windows.Forms.Control.Invoke was created in .NET 1.0. Today, one would use the following signatures:

void Invoke(Action action);
Task InvokeAsync(Action action);

而且它会简单地工作.

尝试迁移到 await，这不再是一个问题.

Try to make the migration to await and this stops being a concern.

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