blocks|key|5562659|text|你不能--在C#的类型系统中，两个委托之间没有关系，即使他们的签名匹配。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|5562660|例如，Func<T,+bool>和Predicate<T>是不相关的。|offset|length|style|CODE|5562661|5562662|此外，假设表达式(sender,+e)+=>+{+/*+do+stuff+*/}的类型为Action<object,+EventArg>是错误的。Lambda表达式本身没有类型。它们将根据上下文转换为委托。|5562663|这就是为什么不能将lambda表达式赋值给var+-因为类型无法推断-因为没有类型。|5562664|var+del+=+(int+i)+=>+i+%2B+1;+++++++++//incorrect
Func<int,+int>+del+=+i+=>+i+%2B+1;++++//correct
CustomDelegate+del+=+i+=>+i+%2B+1;++++//correct


delegate+int+CustomDelegate(int+i);|code-block|syntax|javascript|5562665|entityMap^0|0|3|D|H|C|0|0|8|W|18|O|0|L|3|0|0^^$0|@$1|2|3|4|5|6|7|T|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|U|8|@$D|V|E|W|F|G]|$D|X|E|Y|F|G]]|9|@]|A|$]]|$1|H|3|-4|5|6|7|Z|8|@]|9|@]|A|$]]|$1|I|3|J|5|6|7|10|8|@$D|11|E|12|F|G]|$D|13|E|14|F|G]]|9|@]|A|$]]|$1|K|3|L|5|6|7|15|8|@$D|16|E|17|F|G]]|9|@]|A|$]]|$1|M|3|N|5|O|7|18|8|@]|9|@]|A|$P|Q]]|$1|R|3|-4|5|6|7|19|8|@]|9|@]|A|$]]]|S|$]]

You can't - In C#'s type system there is no relationship between two delegates, even if their signatures match.

For example, <code>Func&lt;T, bool&gt;</code> and <code>Predicate&lt;T&gt;</code> are unrelated.

<hr>

Also, your assumption that the expression <code>(sender, e) =&gt; { /* do stuff */}</code> is of type <code>Action&lt;object, EventArg&gt;</code> is wrong. Lambda expressions don't have a type, per se. They are converted to delegates, depending on the context.

That's why you can't assign a lambda expression to a <code>var</code> - because the type cannot be inferred - because there is no type.

<pre><code>var del = (int i) =&gt; i + 1; //incorrect
Func&lt;int, int&gt; del = i =&gt; i + 1; //correct
CustomDelegate del = i =&gt; i + 1; //correct


delegate int CustomDelegate(int i);
</code></pre>

blocks|key|5562689|text|您不能创建将被委托的类，但是您可以从您的类创建一个委托。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|5562690|考虑一个类：|5562691|public+class+MyClass+
{
++++public+void+OnTimerElapsed(object+sender,+EventArgs+e)
++++{
++++}
}|code-block|syntax|javascript|5562692|现在将您的类方法连接到事件：|5562693|var+obj+=+new+MyClass();
timer.Elapsed+%2B=+obj.OnTimerElapsed;|5562694|您还可以断开它的连接：|5562695|timer.Elapsed+-=+obj.OnTimerElapsed;|5562696|您应该阅读更多关于C#中的事件的内容，比如这里：https://msdn.microsoft.com/en-us/library/aa645739(v=vs.71).aspx|offset|length|5562697|entityMap|0|LINK|mutability|MUTABLE|url|https://msdn.microsoft.com/en-us/library/aa645739(v=vs.71).aspx^0|0|0|0|0|0|0|0|O|1R|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]]|$1|I|3|J|5|6|7|15|8|@]|9|@]|A|$]]|$1|K|3|L|5|F|7|16|8|@]|9|@]|A|$G|H]]|$1|M|3|N|5|6|7|17|8|@]|9|@]|A|$]]|$1|O|3|P|5|F|7|18|8|@]|9|@]|A|$G|H]]|$1|Q|3|R|5|6|7|19|8|@]|9|@$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]]]]

You can't create your class that will be delegate, however you can create a delegate from your class.

Consider a class:

<pre><code>public class MyClass 
{
 public void OnTimerElapsed(object sender, EventArgs e)
 {
 }
}
</code></pre>

Now you connect your class method to the event:

<pre><code>var obj = new MyClass();
timer.Elapsed += obj.OnTimerElapsed;
</code></pre>

You can also disconnect it:

<pre><code>timer.Elapsed -= obj.OnTimerElapsed;
</code></pre>

You should read more about events in C#, like in here: <a href="https://msdn.microsoft.com/en-us/library/aa645739(v=vs.71).aspx" rel="nofollow">https://msdn.microsoft.com/en-us/library/aa645739(v=vs.71).aspx</a>

blocks|key|1212071|text|好的。这很棘手。但我不得不说..。通过使用隐式转换的奇妙世界，这是可能的。试着这样开始..|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1212072|//+define+a+new+class+called+EventCall
public+class+EventCall<T>+{
++++//+this+one+will+be+returned+to+be+executed+directly+after+your+initialization
++++public+T+Handler+{+get;+private+set;+}

++++public+EventCall(T+handler)+{
++++++++if+(handler+==+null)+throw+new+ArgumentNullException("handler");
++++++++this.Handler+=+handler;
++++++++//+the+intercept+code+can+be+inserted+here..
++++++++//+but+i+can't+see+any+point+of+doing+this..
++++}

++++//+this+method+will+return+the+handler+directly+after+the+initialization
++++public+static+implicit+operator+T(EventCall<T>+c)+{
++++++++return+this.Handler;
++++}
}

//+now+you+can+use+it+like
timer.Elapsed+%2B=+new+EventCall<ElapsedEventHandler>((sender,+args)+=>+{+/*+code+to+invoke+*/+});|code-block|syntax|javascript|1212073|这个可以用。我刚刚自己测试过了。但是类型参数T总是需要匹配正确的事件处理程序类型。|offset|length|style|CODE|1212074|这段代码基本上是使用T参数来获取新对象的类型，该类型直接传递给构造函数，然后(通过隐式转换)立即返回。这有点过火了..。但不管怎样。希望这会有帮助..。|1212075|entityMap^0|0|0|M|1|0|A|1|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|R|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|S|8|@$I|T|J|U|K|L]]|9|@]|A|$]]|$1|M|3|N|5|6|7|V|8|@$I|W|J|X|K|L]]|9|@]|A|$]]|$1|O|3|-4|5|6|7|Y|8|@]|9|@]|A|$]]]|P|$]]

Alright. That's tricky. But I have to say.. it's possible by using the wonderful world of implicit conversions. Try starting like this..

<pre><code>// define a new class called EventCall
public class EventCall&lt;T&gt; {
 // this one will be returned to be executed directly after your initialization
 public T Handler { get; private set; }

 public EventCall(T handler) {
 if (handler == null) throw new ArgumentNullException("handler");
 this.Handler = handler;
 // the intercept code can be inserted here..
 // but i can't see any point of doing this..
 }

 // this method will return the handler directly after the initialization
 public static implicit operator T(EventCall&lt;T&gt; c) {
 return this.Handler;
 }
}

// now you can use it like
timer.Elapsed += new EventCall&lt;ElapsedEventHandler&gt;((sender, args) =&gt; { /* code to invoke */ });
</code></pre>

This one works. I've just tested it by myself. But the type-parameter <code>T</code> always needs to match the correct event handler type..

What this code does is basically using the <code>T</code> parameter to get the type for a new object which is directly passed to the constructor and then (via implicit conversion) immediately returned back. It's kinda overkill.. but whatever. Hope that helped..

Basicly, what I want to archive is way to intercept a call to a delegate. I was thinking to define a class that can be used for it. Something like:

<pre><code>timer.Elapsed += new MyClass((sender, e)=&gt; { /* do stuff */});
</code></pre>

How do I define <code>MyClass</code> in a generic way? 

I could let <code>Myclass</code> inherent from <code>ElapsedEventHandler</code>, but than it can only be used for this event. I was thinking to let <code>MyClass</code> inherent from <code>Action&lt;object, EventArg&gt;</code> since you can also write

<pre><code>timer.Elapsed += (sender, e) =&gt; { /* do stuff */ }
</code></pre>

But I did not get that one working. Any suggestions?

How to intercept a delegate call by using a class

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。

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基本上，我想归档的是截获对委托的调用的方法。我在考虑定义一个可以用于它的类。类似于：timer.Elapsed += new MyClass((sender, e)=> { /* do stuff */});如何以通用的方式定义MyClass？我可以让Myclass继承自ElapsedEventHandler，但是它只...

问如何使用类截取委托调用
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问如何使用类截取委托调用EN