Raise C++ event and catch in C#

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Hi All,
I have a managed C++ (.NET) DLL, and I want to raise an event from one of it's methods and catch it in a C# windows application. I've been playing around for a while but can't get it to work.

Can someone post a quick message that will show what lines of code I'd need in my C++ DLL and C# EXE?

Kind Regards,
Chris

Posted 8-Feb-11 0:11am

cr101037

Updated 8-Feb-11 20:00pm

Emilio Garavaglia

v2

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Comments

Manfred Rudolf Bihy 8-Feb-11 6:26am

So why don't you show us what you tried?

cr101037 8-Feb-11 6:41am

Ok, so here's what I've tried...In my C++ code:

//declare delegate (in my .h file)delegate void MyEventHandler(int);

//define event (in my .h file)event MyEventHandler^ Test;

//Fire event from my method (in my .cpp file)Test(35);

That compiles just fine, but not sure if it's right?And then in my C# code:

MyClass.Test += HandleCustomEvent;void HandleCustomEvent(int i){

// Do something useful here.}

Prerak Patel 8-Feb-11 6:46am

MyClass.Test += new System.EventHandler(HandleCustomEvent);

Check the answer

Manfred Rudolf Bihy 8-Feb-11 6:51am

When you said "And then in my C++ code" you probably meant to say C#? So your programs compile and run? What is the exact problem you are having. "I can't get it to work" is not very helpful. Please tell us what your exact problem is.

cr101037 8-Feb-11 7:05am

Yeah sorry I meant C#, I've corrected that now. The error I'm receiving is "MyClass.Test is inaccessible due to its protection level" even though it's declared under public: in my C++ class. One thing I have just thought of, my class is defined as a ref class (public ref class MyClass), would that cause a problem?

3 solutions

Solution 3

Events are not raised and caught, they are not exceptions. They are fired and handled. (Don't say, this is just terminology! I am not sure. Very often terminology is indicative of some misconception.) Now, the events ultimately are containers for delegate and invocation mechanism, there is nothing different from regular methods when it comes to inter-operation.

In the world of managed code, there in no barrier between C++/CLI (are you really using "managed C++"? This is obsolete dialect replaced with C++/CLI, distinctly different) and C#. One exception in value semantic for reference (C++/CLI ref) types — it is only specific to C++/CLI, so for C# you need to use reference semantic only (through "^" types and objects obtained via gcnew or "%"). And, of course, if you make mixed-mode C++ project (managed+unmanaged) you can use unmanaged code with C# only via System.Runtime.InteropServices.DLLImportAttribute (P/Invoke).

—SA

Posted 8-Feb-11 12:11pm

Sergey Alexandrovich Kryukov

Updated 8-Feb-11 12:39pm

v3

Comments

Espen Harlinn 8-Feb-11 18:20pm

Good effort, my 5

Nish Nishant 8-Feb-11 18:51pm

>> Events are not raised and caught, they are not exceptions <<

Uhm, I think that's not correct. Events are "raised" or "fired" - and they both mean the same thing.

Exceptions are "thrown" and "caught".

Sergey Alexandrovich Kryukov 8-Feb-11 19:31pm

See my comment below (failed to put in the tree under yours)
--SA

Sergey Alexandrovich Kryukov 8-Feb-11 19:31pm

Eh... not quite. I agree that events are also "raised", but I suggest to avoid it, here is why: the terms are overloaded. The exception's "throw" keyword is a tradition going from C++ culture; in other (not just one, some are very influential and important) languages "raise" is used instead of throw (also "self" instead of "this"). We should better honor that, it helps to be more accurate. After all, we usually express many notions here in terms of Computer Science abstracted from particular language.
--SA

Nish Nishant 8-Feb-11 19:35pm

Tell this to Microsoft. VB.NET actually has a keyword called RaiseEvent :-)

BTW I personally prefer and use Fire over Raise since I feel Fire is a more appropriate word.

Sergey Alexandrovich Kryukov 8-Feb-11 19:48pm

I would if Microsoft was a bit more responsive. "RaiseEvent"? Ok, I already told I was agree with you on "raise" for events. By the way, Microsoft inherited most of .NET from Delphi (because Delphi architect later architectured .NET and C#), but C# syntax was C-like. Eclectic terminology is usual for Microsoft (and would say they are not very picky, more exactly). (I always was very unhappy with the term "overloading", very poor (what's "loading" where?) and a permanent cause of lamer's mix-ups; well, this is not Microsoft...)
--SA

Solution 1

C#

// This is in form_load for example
MyType var = new MyType();
var.MyEvent += new System.EventHandler(this.MyHandler);
// this is outside form_load, the event handler:
private void MyHandler(object sender, System.EventArgs e)
{
    // handle var.MyEvent here.

}

Posted 8-Feb-11 0:44am

Prerak Patel

Updated 8-Feb-11 0:45am

v2

Comments

cr101037 8-Feb-11 7:12am

Hi Prerak,
This is the error I get:
'MyClass.Test' is inaccessible due to its protection level

And this is my class definition:

delegate void MyEventHandler(int);
public ref class MyClass
{

public:
MyClass();
~MyClass();

...

event MyEventHandler^ Test;
};

Sergey Alexandrovich Kryukov 8-Feb-11 18:40pm

See answer by Nishant and my comment.
--SA

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Nish Nishant · Accepted Answer · 2011-02-08T05:22:00

Solution 2

Your delegate is not marked public, so it will default to internal. So even though your class is public, and so is the event member within the class, the event type itself will not be accesible. Mark the delegate to be public too.

Posted 8-Feb-11 5:22am

Nish Nishant

Comments

Espen Harlinn 8-Feb-11 18:20pm

Nicely spotted, a 5

Nish Nishant 8-Feb-11 18:45pm

Thank you, Espen.

Sergey Alexandrovich Kryukov 8-Feb-11 18:21pm

That's correct, my 5, let me clarify...
--SA

Nish Nishant 8-Feb-11 18:45pm

Thank you.

Sergey Alexandrovich Kryukov 8-Feb-11 18:23pm

For OP: 1) internal is the same as public with one difference: invisible outside declaring assembly; 2) protected internal is the same as protected with one difference: invisible even in derived classes outside declaring assembly; 3) for Reflection, all members are equally visible if you know how to look.
--SA