blocks|key|320215|text|您可以传递一个委托：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|320216|public+void+MyFunction(Delegate+d)
{
++++//+do+something+with+the+method+group
}|code-block|syntax|javascript|320217|但是，您必须在调用该方法时指定委托类型：|320218|MyFunction(new+Func<object,+object,+bool>(Object.Equals));|320219|注意:上面的代码不是传递方法组，而是传递单个方法...我认为传递一个方法组是不可能的。你为什么要这么做呢？|320220|entityMap^0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|Q|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|R|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|S|8|@]|9|@]|A|$]]|$1|M|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|N|$]]

You can pass a delegate :

<pre><code>public void MyFunction(Delegate d)
{
 // do something with the method group
}
</code></pre>

However you will have to specify the delegate type when calling the method :

<pre><code>MyFunction(new Func&lt;object, object, bool&gt;(Object.Equals));
</code></pre>

Note : the code above is not passing a method group but a single method... I don't think it is possible to pass a method group. Why would you want to do that ?

blocks|key|320226|text|我认为这里有一个重要的问题：，如果你有机会被传递一个方法组，你会怎么做？|type|unstyled|depth|inlineStyleRanges|offset|length|style|BOLD|entityRanges|data|320227|请记住，方法组只是一组方法的名称-可能有一个或多个-它们可能是重载或扩展方法。方法组不是一个保留在编译代码中的概念-编译器支持从方法组到委托的转换-但为了使这成为可能，编译器必须能够准确地解析您想要传递的方法。|320228|只有当函数明确定义方法的签名时，方法组才能作为函数的参数有效。因此，例如:可以向public+void+MyFunction(+Func<int>+f+)传递一个方法组。|CODE|320229|最接近的方法是编写一个接受Delegate类型的函数：|320230|public+void+MyFunction(+Delegate+d+)+{+...+}|code-block|syntax|javascript|320231|但是您仍然不能传入方法组，因为没有从方法组到委托的转换。您必须强制转换为特定的委托签名：|320232|//+call+MyFunction+with+a+particular+delegate
MyFunction(+(Func<string>)myObj.ToString+);++//+method+group+conversion+may+occur|320233|entityMap^0|E|M|0|0|14|11|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|X|8|@$9|Y|A|Z|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|10|8|@]|D|@]|E|$]]|$1|H|3|I|5|6|7|11|8|@$9|12|A|13|B|J]]|D|@]|E|$]]|$1|K|3|L|5|6|7|14|8|@]|D|@]|E|$]]|$1|M|3|N|5|O|7|15|8|@]|D|@]|E|$P|Q]]|$1|R|3|S|5|6|7|16|8|@]|D|@]|E|$]]|$1|T|3|U|5|O|7|17|8|@]|D|@]|E|$P|Q]]|$1|V|3|-4|5|6|7|18|8|@]|D|@]|E|$]]]|W|$]]

I think an important question here is: what would you do with a method group if you could ever be passed one?

Keep in mind, a method group is just a name for a set of methods - there may be one or more - and they may be overloads or extension methods. Method groups are not a concept that is preserved in compiled code - the compiler supports conversions from method groups to delegates - but in order for this to be possible the compiler must be able to resolve without any ambiguity exactly what method you intend to pass.

Method groups are only valid as parameters to functions if the function clearly defines the signature of the method. So, for example: <code>public void MyFunction( Func&lt;int&gt; f )</code> can be passed a method group.

The closest you can come is to write a function that accepts the type Delegate:

<pre><code>public void MyFunction( Delegate d ) { ... }
</code></pre>

but you will still not be able to pass method groups in because there is no conversion from method group to Delegate. You will have to cast to a particular delegate signature:

<pre><code>// call MyFunction with a particular delegate
MyFunction( (Func&lt;string&gt;)myObj.ToString ); // method group conversion may occur
</code></pre>

blocks|key|3072712|text|我认为你可以像这样使用签名：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3072713|MyFunc<T>(EventHandler<T>+newDelegate)
{
++++object+storedDelegate+=+newDelegate;
++++//+after+that+you+can+use+storedDelegate+later
}|code-block|syntax|javascript|3072714|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

I think you could use signature like this:

<pre><code>MyFunc&lt;T&gt;(EventHandler&lt;T&gt; newDelegate)
{
 object storedDelegate = newDelegate;
 // after that you can use storedDelegate later
}
</code></pre>

blocks|key|322013|text|请求者想要这样做是因为他想要关于方法组的元数据，这些元数据对于组中的任何方法都是相同的(比如name)，或者他想对组中的所有方法做一些事情。我相信nameof+(C#+Reference)在这里是最有用的。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|322014|我按照他最初的期望定义了MyFunction，但重要的是要注意，无论它做什么，都只适用于one方法签名。如果MethodInfo提供了函数所需的所有信息，则实际上可能不需要调用此函数。|style|BOLD|322015|public+void+MyFunction(Delegate+d)
{
++++//+do+something+with+d
}|code-block|syntax|javascript|322016|然后，我们将提供一个包装器，该包装器接受methodName、类型以及可选的调用对象。调用对象是而不是生成委托所需的，即使它是一个实例方法，但如果它为空，则实际执行委托可能会失败。为静态方法提供调用对象将导致绑定错误，即使对于创建委托也是如此。我已经编写了下面的方法来返回静态方法和实例方法，并将任何实例方法绑定到调用者，而静态方法则绑定到null。当调用者是实例时，您可以修改它以跳过静态方法，反之亦然。|322017|public+void+MyFunctionMethodGroup(string+methodName,+Type+type,+object+caller)
{
++++var+methods+=+type.GetMethods().Where(x+=>+x.Name+==+methodName);
++++foreach(var+method+in+methods)
++++{
++++++++Delegate+myDelegate+=+method.CreateDelegate(Expression.GetDelegateType(
++++++++++++method.GetParameters().Select(x+=>+x.ParameterType)
++++++++++++.Concat(new[]+{+method.ReturnType+})
++++++++++++.ToArray()),+method.IsStatic+?+null+:+caller);
++++++++MyFunction(myDelegate);
++++}
}|322018|这里有几个常用的例子。|322019|静态方法|322020|MyFunctionMethodGroup(nameof(String.IsNullOrEmpty),+typeof(String),+null);|322021|实例方法|322022|请注意，即使函数是实例函数，也可以使用类名中的任何一个调用函数。如果您不需要调用该方法，并且没有调用者，那么这种方法很好用。您也可以从实例调用它，而不需要显式地编写类名。|322023|string+xyz+=+"2";
MyFunctionMethodGroup(nameof(String.Contains),+typeof(String),+xyz);
MyFunctionMethodGroup(nameof(xyz.Contains),+xyz.GetType(),+xyz);|322024|高级案例|322025|扩展方法|322026|值得记住的是，扩展方法是作为静态方法在定义它们的名称空间中调用的。如果你需要实例参数来做你想在MyFunction中做的事情，那么它必须作为一个新的参数传入，与调用者分开，这个参数将是null，因为扩展方法是静态的。|322027|泛型方法|322028|此外，上面的代码不能与泛型方法一起正常工作。下面是一个应用该方法泛型类型的示例。|322029|+++public+void+MyFunctionMethodGroup(string+methodName,+Type+type,+object+caller+=+null,+params+Type[]+genericParameters)
++++{
++++++++//GetMethods+only+returns+public+methods.+If+you+need+protected/private,+modify+as+appropriate.
++++++++var+methods+=+type.GetMethods().Where(x+=>+x.Name+==+methodName);
++++++++foreach+(var+method1+in+methods)
++++++++{
++++++++++++MethodInfo+method+=+method1.IsGenericMethod+?+method1.MakeGenericMethod(genericParameters)+:+method1;
++++++++++++Type+delegateType+=+Expression.GetDelegateType(
++++++++++++++++method.GetParameters().Select(x+=>+x.ParameterType)
++++++++++++++++.Concat(new[]+{+method.ReturnType+})
++++++++++++++++.ToArray());
++++++++++++Delegate+myDelegate+=+method.CreateDelegate(delegateType,+method.IsStatic+?+null+:+caller);
++++++++++++MyFunction(myDelegate);
++++++++}
++++}|322030|泛型类|322031|如果传入的类没有在Type参数中定义的泛型类型，则上面的方法可能不完全支持泛型类中的方法。|322032|输出/参考参数|322033|所编写的代码不支持输出或引用参数。它也可能不支持ref参数。|322034|entityMap|0|LINK|mutability|MUTABLE|url|https://docs.microsoft.com/en-us/dotnet/csharp/language-reference/keywords/nameof^0|21|L|0|0|18|3|0|0|1C|A|0|0|0|0|4|0|0|0|4|0|0|0|0|4|0|0|4|0|0|0|4|0|0|0|0|3|0|0|0|7|0|0^^$0|@$1|2|3|4|5|6|7|1U|8|@]|9|@$A|1V|B|1W|1|1X]]|C|$]]|$1|D|3|E|5|6|7|1Y|8|@$A|1Z|B|20|F|G]]|9|@]|C|$]]|$1|H|3|I|5|J|7|21|8|@]|9|@]|C|$K|L]]|$1|M|3|N|5|6|7|22|8|@$A|23|B|24|F|G]]|9|@]|C|$]]|$1|O|3|P|5|J|7|25|8|@]|9|@]|C|$K|L]]|$1|Q|3|R|5|6|7|26|8|@]|9|@]|C|$]]|$1|S|3|T|5|6|7|27|8|@$A|28|B|29|F|G]]|9|@]|C|$]]|$1|U|3|V|5|J|7|2A|8|@]|9|@]|C|$K|L]]|$1|W|3|X|5|6|7|2B|8|@$A|2C|B|2D|F|G]]|9|@]|C|$]]|$1|Y|3|Z|5|6|7|2E|8|@]|9|@]|C|$]]|$1|10|3|11|5|J|7|2F|8|@]|9|@]|C|$K|L]]|$1|12|3|13|5|6|7|2G|8|@$A|2H|B|2I|F|G]]|9|@]|C|$]]|$1|14|3|15|5|6|7|2J|8|@$A|2K|B|2L|F|G]]|9|@]|C|$]]|$1|16|3|17|5|6|7|2M|8|@]|9|@]|C|$]]|$1|18|3|19|5|6|7|2N|8|@$A|2O|B|2P|F|G]]|9|@]|C|$]]|$1|1A|3|1B|5|6|7|2Q|8|@]|9|@]|C|$]]|$1|1C|3|1D|5|J|7|2R|8|@]|9|@]|C|$K|L]]|$1|1E|3|1F|5|6|7|2S|8|@$A|2T|B|2U|F|G]]|9|@]|C|$]]|$1|1G|3|1H|5|6|7|2V|8|@]|9|@]|C|$]]|$1|1I|3|1J|5|6|7|2W|8|@$A|2X|B|2Y|F|G]]|9|@]|C|$]]|$1|1K|3|1L|5|6|7|2Z|8|@]|9|@]|C|$]]|$1|1M|3|-4|5|6|7|30|8|@]|9|@]|C|$]]]|1N|$1O|$5|1P|1Q|1R|C|$1S|1T]]]]

The asker wants to do this because he wants meta data about the method group that is the same for any method in the group (such as name) or he wants to do something with all of the methods in the group. I believe <a href="https://docs.microsoft.com/en-us/dotnet/csharp/language-reference/keywords/nameof" rel="nofollow noreferrer">nameof (C# Reference)</a> is what would prove most useful here.

I define MyFunction as he initially expected, but it is important to note that whatever this does is only applying to one method signature. This may not actually need to be called if MethodInfo gives everything you need about the function.

<pre><code>public void MyFunction(Delegate d)
{
 // do something with d
}
</code></pre>

Then we will provide a wrapper that takes a methodName, type, and optionally a calling object. The calling object is not required to generate the delegate even if it is an instance method, but actually executing the delegate may fail if it is null. Providing a calling object for a static method will cause binding errors though even for creating the delegate. I have written the method below to return both static and instance methods and bind any instance methods to the caller whereas static methods bind to null. You could modify it to skip static methods when the caller is an instance and vice-versa.

<pre><code>public void MyFunctionMethodGroup(string methodName, Type type, object caller)
{
 var methods = type.GetMethods().Where(x =&gt; x.Name == methodName);
 foreach(var method in methods)
 {
 Delegate myDelegate = method.CreateDelegate(Expression.GetDelegateType(
 method.GetParameters().Select(x =&gt; x.ParameterType)
 .Concat(new[] { method.ReturnType })
 .ToArray()), method.IsStatic ? null : caller);
 MyFunction(myDelegate);
 }
}
</code></pre>

Here are a few calling examples.

Static method

<pre><code>MyFunctionMethodGroup(nameof(String.IsNullOrEmpty), typeof(String), null);
</code></pre>

Instance method

Notice that you can call the function with from either the class name even if it is an instance function. This goes well if you do not need to invoke the method and don't have a caller. You can also invoke it from an instance without needing to explicitly write the class name.

<pre><code>string xyz = "2";
MyFunctionMethodGroup(nameof(String.Contains), typeof(String), xyz);
MyFunctionMethodGroup(nameof(xyz.Contains), xyz.GetType(), xyz);
</code></pre>

Advanced Cases

Extension Methods

It is worth remembering that extension methods are called as static methods on the namespace in which they are defined. If you needed the instance parameter for what you wanted to do in MyFunction, then it would have to be passed in as a new parameter separate from the caller which would be null as extension methods are static.

Generic Methods

Additionally, the code above does not work properly with generic methods. Here is an example of apply the generic type of the method.

<pre><code> public void MyFunctionMethodGroup(string methodName, Type type, object caller = null, params Type[] genericParameters)
 {
 //GetMethods only returns public methods. If you need protected/private, modify as appropriate.
 var methods = type.GetMethods().Where(x =&gt; x.Name == methodName);
 foreach (var method1 in methods)
 {
 MethodInfo method = method1.IsGenericMethod ? method1.MakeGenericMethod(genericParameters) : method1;
 Type delegateType = Expression.GetDelegateType(
 method.GetParameters().Select(x =&gt; x.ParameterType)
 .Concat(new[] { method.ReturnType })
 .ToArray());
 Delegate myDelegate = method.CreateDelegate(delegateType, method.IsStatic ? null : caller);
 MyFunction(myDelegate);
 }
 }
</code></pre>

Generic Classes

The method above may not fully support methods in generic classes if the class is passed in without the generic types defined in the Type parameter.

Output/Reference Parameters

The code as written does not support output or reference parameters. It may not support ref parameters either.

I'd like write a function like the following

<pre><code>// The type 'MethodGroup' below doesn't exist. This is fantasy-code.
public void MyFunction(MethodGroup g)
{
 // do something with the method group
}
</code></pre>

The later, I could call <code>MyFunction</code> with any method group. Something like this.

<pre><code>MyFunction(Object.Equals)
</code></pre>

If I commit to a signature, then things work fine.

<pre><code>public void MyFunction(Func&lt;object, object, bool&gt; f)
{
 // do something with known delegate
}
...
MyFunction(Object.Equals)
</code></pre>

The method group <code>Object.Equals</code> is happily coerced into the known delegate type <code>Func&lt;object, object, bool&gt;</code>, but I don't want to commit to a particular signature. I'd like to pass any method group to <code>MyFunction</code>. 

Method groups cannot be converted to <code>System.Object</code>

<pre><code>public void MyFunction(object o)
{
 // do something with o
}
...
MyFunction(Object.Equals) // doesn't work
</code></pre>

I think that everyone's forgotten braces on a method call and discovered this at some point. I'm hoping that this doesn't mean that method groups aren't (or can't be converted) to first class objects. 

I don't think that Linq expressions will give the kind of generality I'm looking for, but I could certainly be missing something.

I should also mention that it would be fine if the method group contained overloads, provided I have a way of inspecting the method group.

What would I do with a method group? I could print all the signatures of all the the methods in the group (overloads, extension methods etc), or I could 'invoke' the group with some arguments (have it resolve to the correct overload in the group if possible). There are other ways to do these things but they are some things you might want to do with a method group.

As several people have mentioned, I can accept a <code>Delegate</code>, and cast to a particular known delegate type when I call <code>MyFunction</code>.

<pre><code>public void MyFunction(Delegate d)
{
 // do something with d
}
...
MyFunction((Func&lt;object, object, bool&gt;)Object.Equals)
</code></pre>

But this isn't quite the same as passing the entire method group. This selects one method from the group and converts it to a particular delegate. I would really like to pass the whole group in one shot.

Is it possible to pass an arbitrary method group as a parameter to a method?

编译器

我想写一个如下所示的函数// The type 'MethodGroup' below doesn't exist.  This is fantasy-code.public void MyFunction(MethodGroup g){    // do something with the method group...

问可以将任意方法组作为参数传递给方法吗？
EN

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问可以将任意方法组作为参数传递给方法吗？
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