how to pass Form handle to unmanaged code

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Gregory Khra - 26 Jun 2007 23:22 GMT

How can I pass a Windows Form handle to unmanaged DLL that expects HWND?
Even if I have a wrapper calss between managed C# and unmanaged C++, IntPtr
does not by default cast to HWND. Should I force it? Can somebody give an
example?
Gregory

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Hans-Gerd Sandhagen - 27 Jun 2007 06:06 GMT

Gregory Khra schrieb:

> How can I pass a Windows Form handle to unmanaged DLL that expects HWND?
> Even if I have a wrapper calss between managed C# and unmanaged C++, IntPtr
> does not by default cast to HWND. Should I force it? Can somebody give an
> example?
> Gregory

Normally that should not be a problem. Example:

C++ DLL:

#include <windows.h>

void NativeFct (HWND hWnd);

C# Wrapper:

class NativeMethods {
[DllImport("my.dll", EntryPoint = "NativeFct")]
public static extern void NativeFct(IntPtr hWnd);
}

C# Form:

class MyForm : Form {
void MyFunc () {
...
NativeMethods(this.Handle);
...
}
}

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Gregory Khra - 27 Jun 2007 17:24 GMT

> Normally that should not be a problem.

I am getting a compiler error: cannot convert parameter ... from
'System::IntPtr' to 'HWND'. This error was the reason for my post.
Gregory

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Mattias Sjögren - 27 Jun 2007 19:46 GMT

>I am getting a compiler error: cannot convert parameter ... from
>'System::IntPtr' to 'HWND'. This error was the reason for my post.

Then I guess you're using C++ even though your original post said C#.

In C++ you want to call IntPtr::ToPointer and then cast the returned
void* to HWND.

Mattias

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Mattias Sjögren [C# MVP] mattias @ mvps.org
http://www.msjogren.net/dotnet/ | http://www.dotnetinterop.com
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how to pass Form handle to unmanaged code

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