不确定使用 lambdas 处理这个 c# 事件是如何工作的，有人可以向我解释一下吗？

Question

I was looking for a way to convert vb event handling to c# since i am implementing something and, after reading this post ( How do I Convert from Anonymous Event Handlers in C# to VB.Net ), i tried to copy the lambda structure, and somehow it worked, but i have NO IDEA. How it does, can someonoe please explain it to me? Or at least guide me to a link for a tutorial or something that helps me understand whats going on in here... I mean, i can get out with this since it, somehow, worked, but i want to understand whats going on rather than just, "get the job done".

Class.Event += Class.Delegate((sometext)) => {eventhandlemethod(sometext);});
eventhandlemethod(string s)
{
   MessageBox.Show(s);
}

Thanks in advance!

Answer 1

I am not familiar with VB.NET but an anonymous Function or Action as it would be in the case of an Eventhandler is basically just a short form of writing.

But what is the line

Class.Event += Class.Delegate((sometext) => {eventhandlemethod(sometext);});

telling you?

1. You have an Event, and you add the handler (obviously).

2. You have added an anonymous method as Eventhandler and created a Delegate from it.

    Class.Delegate(<anoymous method, matching the siganture of the handler>);

3. Your anonymous method looks like this

   (sometext) => {eventhandlemethod(sometext);}

This anonymous method (short lamba) consists of two parts

siganture => body

In Your case the signature gets eh "sometext". Derived from the rest of your code, this seems to be a string. And since eventhandlers always have void as return value, your method, would you have written a normal method, would look like this:

private void (string sometext)
{
}

which is basically, what your eventhandlemethod looks like. You could write this lambda like this as well.

(string sometext) => {eventhandlemethod(sometext);}

This shows you the expected intput type. But you can ommit this usually.

So just as goodie: you could have written

1. with a "normal" method, since you already have it

   Class.Event += Class.Delegate(eventhandlemethod);

2. with a lambda

    Class.Event += Class.Delegate(sometext => MessageBox.Show(sometext));

if you have multiple input variables, put them in brackets

(string s, int i, bool b) => Console.WriteLine($"{s}:{i}:{b}");

and of course, you can ommit the types as well leaving you:

(s, i, b) => Console.WriteLine($"{s}:{i}:{b}");

I hope i could clarify it a bit for you.