How can we use callback function in C#

Question

How can we use callback function in C#?

Can you give a more concrete example of what you want? Your question is too generic to answer. — Oded, Jun 22 '10 at 10:05
possible duplicate of [What is a callback?](http://stackoverflow.com/questions/2139812/what-is-a-callback) — Hans Olsson, Jun 22 '10 at 10:06
Callbacks are used in c++ as a special cases of remote calls that execute as part of a single thread. A callback is issued in the context of a remote call. Any remote procedure defined as part of the same interface as the static callback function can call the callback function.i want to use same cases in c# so i am specifially want to know about this. So i want to use — vishal_niist, Jun 22 '10 at 10:15

score 4 · Accepted Answer · answered Jun 22 '10 at 10:30

I think what you are looking for is "delegates". For example:

public MyClass
{
  public delegate void MyCallback(object sender, string MyArg);

  public string DoSomeWork(string Foo, MyCallback mcb)
  {
    mcb(this, Foo);
    return Foo;
  }
}

You can also use delegates to define events. For example, if you wanted an event in MyClass called "OnMyCallback", define it using:

...
public event MyCallback OnMyCallback;
...

Cheers, Adam

score 2 · Answer 2 · answered Jun 23 '10 at 03:36

Reading the questions as: "I want to call a native c++ callback from C#".

You need to create a delegate on the managed/C# side of the boundary.

C++:

DECLARE_CALLBACK(SampleChannelCallback, void, (void* ptr, uint id, void* data));

C#:

[UnmanagedFunctionPointerAttribute(CallingConvention.Cdecl)]
delegate void NativeCallbackDelegate(IntPtr ptr, uint id, IntPtr data);

If you are using SWIG to create your native wrapper, then add the follow to your SwigUtil.h.

#if defined(SWIG)
// Callback declare macro allows for SWIG to automatically construct a macro for a target language for the macros
#define DECLARE_CALLBACK(NAME, RETURNTYPE, PARAMS) typedef void* NAME; %callback_typemap( NAME )
#else
#define DECLARE_CALLBACK(NAME, RETURNTYPE, PARAMS) typedef RETURNTYPE ( NAME ) PARAMS 
#endif

As your question was not very clear, I'm going to leave it there. If you want more information then please ask in the comments.

HTH,

score 0 · Answer 3 · answered Jun 23 '10 at 03:13

0

Or are you talking about C# .NET event handlers (expanding on the delegates answer)?

answered Jun 23 '10 at 03:13

Ogre Psalm33

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How can we use callback function in C#

3 Answers3