blocks|key|2113787|text|我认为SyncWithInfo签名必须使用EventArg的explict类型。因此，方法签名看起来如下：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|2113788|public+void+SyncWithInfo(Action<object,+DataGridViewCellEventArgs>+cellValueChanged,
++++int+indexValeurFr,+int+indexValeurEn,+int+indexUnite)|code-block|syntax|javascript|2113789|entityMap^0|3|C|L|8|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@$9|N|A|O|B|C]|$9|P|A|Q|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|R|8|@]|D|@]|E|$I|J]]|$1|K|3|-4|5|6|7|S|8|@]|D|@]|E|$]]]|L|$]]

I think that the <code>SyncWithInfo</code> signature has to use the explict type for <code>EventArg</code>. so that the method signature would look like: 

<pre><code>public void SyncWithInfo(Action&lt;object, DataGridViewCellEventArgs&gt; cellValueChanged,
 int indexValeurFr, int indexValeurEn, int indexUnite)
</code></pre>

blocks|key|2113835|text|接受的答案有解决办法，但试图提供一点解释：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2113836|通常，可以将派生类型分配给它们的基类型：|2113837|EventArgs+e+=+new+DataGridViewCellEventArgs();|code-block|syntax|javascript|2113838|然而，当您开始处理泛型(这就是您的操作，泛型委托)时，事情会变得有点奇怪。你必须开始处理一个叫做方差的概念。默认情况下，泛型不是协变量。协方差意味着您可以使用派生类型作为类型参数。逆反心理意味着你可以走另一条路。|2113839|一些泛型(如IEnumerable+)被标记为协变量(使用out作为它们的类型参数)。所以你才能做到：|2113840|IEnumerable<object>+=+new+List<String>();|2113841|操作委托不是协变量的，因此示例代码不会编译。|2113842|MSDN上的协方差和反方差|offset|length|2113843|entityMap|0|LINK|mutability|MUTABLE|url|http://msdn.microsoft.com/en-us/library/dd799517%2528v=vs.110%2529.aspx^0|0|0|0|0|0|0|0|0|4|0|0^^$0|@$1|2|3|4|5|6|7|12|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|13|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|14|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|15|8|@]|9|@]|A|$]]|$1|K|3|L|5|6|7|16|8|@]|9|@]|A|$]]|$1|M|3|N|5|F|7|17|8|@]|9|@]|A|$G|H]]|$1|O|3|P|5|6|7|18|8|@]|9|@]|A|$]]|$1|Q|3|R|5|6|7|19|8|@]|9|@$S|1A|T|1B|1|1C]]|A|$]]|$1|U|3|-4|5|6|7|1D|8|@]|9|@]|A|$]]]|V|$W|$5|X|Y|Z|A|$10|11]]]]

The accepted answer has the solution, but to try and provide a bit of explanation:

Normally, you can assign derived types to their base types:

<pre><code>EventArgs e = new DataGridViewCellEventArgs();
</code></pre>

However, when you start dealing with generics (which is what your action is, a generic delegate), things get a little weird. You have to start dealing with a concept called variance. By default, generics are not covariant. Covariance means that you are allowed to use a derived type as a type argument. Contravariance means you can go the other way.

Some generics, like IEnumerable, are marked as covariant (by using out T as their type parameter). That's why you can do:

<pre><code>IEnumerable&lt;object&gt; = new List&lt;String&gt;();
</code></pre>

Action delegates are not covariant, and so the sample code will not compile.

Covariance and Contravariance on <a href="http://msdn.microsoft.com/en-us/library/dd799517%28v=vs.110%29.aspx" rel="nofollow">MSDN</a>.

blocks|key|1835437|text|“LordTakkera”的解释是错误的(对不起)。这与这里与泛型相关的方差无关。对于普通(非泛型)委托，您也会遇到同样的问题。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1835438|方法可以接受具有比方法标头中指定的参数类型更多的派生类型的值。这里我们必须考虑的方法是我们希望作为参数传递给另一个方法的事件处理程序。如果此事件处理程序需要DataGridViewCellEventArgs类型的参数，则它将不接受派生较少的EventArgs类型的参数。|offset|length|style|CODE|1835439|如果您可以将此事件处理程序作为委托传递给另一个方法的Action<object,+EventArgs>类型的参数，则另一个方法可以调用我们的事件处理程序并传递给它一个EventArgs参数；但是，事件处理程序需要一个DataGridViewCellEventArgs参数。|1835440|另一方面，相反的情况起作用。|1835441|private+void+AcceptsEventHandler(Action<object,+DataGridViewCellEventArgs>+handler)
{
++++//+handler+is+SomeEventHandler+if+we+call:
++++//+++++++++++AcceptsEventHandler(SomeEventHandler);

++++handler(this,+new+DataGridViewCellEventArgs(1,+2));
}

private+void+SomeEventHandler(object+sender,+EventArgs+e)
{
+++//+We+are+getting+a+DataGridViewCellEventArgs+as+second+argument+here,+which+is+ok.
}|code-block|syntax|javascript|1835442|这样做是可行的：|1835443|AcceptsEventHandler(SomeEventHandler);|1835444|entityMap^0|0|26|P|3C|9|0|Q|P|2B|9|30|P|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|W|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|X|8|@$D|Y|E|Z|F|G]|$D|10|E|11|F|G]]|9|@]|A|$]]|$1|H|3|I|5|6|7|12|8|@$D|13|E|14|F|G]|$D|15|E|16|F|G]|$D|17|E|18|F|G]]|9|@]|A|$]]|$1|J|3|K|5|6|7|19|8|@]|9|@]|A|$]]|$1|L|3|M|5|N|7|1A|8|@]|9|@]|A|$O|P]]|$1|Q|3|R|5|6|7|1B|8|@]|9|@]|A|$]]|$1|S|3|T|5|N|7|1C|8|@]|9|@]|A|$O|P]]|$1|U|3|-4|5|6|7|1D|8|@]|9|@]|A|$]]]|V|$]]

The explanation of @LordTakkera is wrong (sorry). It has nothing to do with the variance associated to generics here. You will get the same problem with a plain (non-generic) delegate.

A method can accept values having types that are more derived than the argument type specified in the method header. The method we have to consider here is the event handler that we want to pass as argument to another method. If this event handler expects an argument of type <code>DataGridViewCellEventArgs</code> it will not accept an argument of type <code>EventArgs</code> which is less derived.

If you could pass this event handler as delegate to an argument of type <code>Action&lt;object, EventArgs&gt;</code> of another method, this other method could call our event handler and pass it an <code>EventArgs</code> argument; however, the event handler expects a <code>DataGridViewCellEventArgs</code> argument.

On the other hand, the opposite situation works.

<pre><code>private void AcceptsEventHandler(Action&lt;object, DataGridViewCellEventArgs&gt; handler)
{
 // handler is SomeEventHandler if we call:
 // AcceptsEventHandler(SomeEventHandler);

 handler(this, new DataGridViewCellEventArgs(1, 2));
}

private void SomeEventHandler(object sender, EventArgs e)
{
 // We are getting a DataGridViewCellEventArgs as second argument here, which is ok.
}
</code></pre>

This works:

<pre><code>AcceptsEventHandler(SomeEventHandler);
</code></pre>

I'm trying to pass an event handler to one of my method. This might look stupid but I can't seem to find a way to do it.

I have the red few questions here around on SO but I still don't get over it.

I have the following method signature 

<pre><code>public void SyncWithInfo(Action&lt;object, EventArgs&gt; cellValueChanged,
 int indexValeurFr, int indexValeurEn, int indexUnite)
</code></pre>

And where I'm trying to call it using this piece of code

<pre><code>private void myMethod()
{
 dgvform.SyncWithInfo(dgvform_CellValueChanged, valeur.Index,
 valeurEN.Index, unite.Index);
}

private void dgvform_CellValueChanged(object sender, DataGridViewCellEventArgs e)
{
 //stuff
}
</code></pre>

I have the following error : 

<blockquote>
 cannot convert from 'method group' to <code>'System.Action&lt;object, System.EventArgs&gt;'</code>
</blockquote>

From what I have red somewhere <a href="https://stackoverflow.com/a/13116032/2145522">here</a> on SO refering a method directly by its name without any parameter is considered a 'method group' since there could be X overload of that method.

So here is my question : How can I pass my event handler as an argument for my method?

Passing an eventhandler as a method argument

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

文章

问答

视频

学习中心

腾讯云实验室

直播

竞赛

腾讯云代码分析专区

腾讯iOA零信任安全管理系统专区

腾讯云架构师技术同盟交流圈

腾讯云数据库专区

腾讯云顾问专区

腾讯云原生专区

腾讯混元专区

腾讯云TCE专区

腾讯云Lighthouse专区

腾讯云HAI专区

腾讯云Edgeone专区

腾讯云存储专区

腾讯云智能专区

腾讯轻联专区 

腾讯云开发专区

TAPD专区

腾讯轻量云游戏服专区

腾讯云最具价值专家

腾讯云架构师技术同盟

腾讯云创作之星

腾讯云开发者先锋 

腾讯云代码助手

CODING DevOps

Cloud Studio

SDK中心

API中心

命令行工具

我试图将一个事件处理程序传递给我的方法之一。这看起来很愚蠢，但我似乎找不到办法去做。我这里有几个问题，所以我还是没能解决。我有以下方法签名public void SyncWithInfo(Action<object, EventArgs> cellValueChanged, int indexValeurFr, ...

问传递一个均数作为方法参数
EN

Stack Overflow用户

社区

活动

圈层

关于

腾讯云开发者

热门产品

热门推荐

更多推荐

问传递一个均数作为方法参数EN