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C# RegisterClassEx/WNDCLASSEX problem

Posted on 2008-10-30
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Last Modified: 2013-12-17
Hello all,

I am having trouble registering a new window class in C# using RegisterClassEx.  My application already heavily uses the WinAPI via pInvoke (i.e. DllImport statements) for other functions, and that part isn't the problem, I don't think (but am open to the possibility.)

Basically, when I call CreateWindowEx, it fails with error 1407, which basically says that my class name is undefined (which I agree with.)  I simply can't seem to figure out the WNDCLASSEX structure and how to use it in C#.  Could anyone please post and/or send me C# sample code that will successfully register a new window class (named, for example's sake "sample_window") that will allow a call to CreateWindowEx similar to the following to succeed??

            IntPtr myNewSampleWindowHWND = CreateWindowEx(WS_EX_TOPMOST, "sample_window", "", WS_VISIBLE, 0, 0, 500, 500, this.Handle, IntPtr.Zero, IntPtr.Zero, IntPtr.Zero);

My goal is to create a blank (in the sense of WinAPI programming) topmost window that I can get a Graphics object from and draw a rectangle on.  Other than what I specifically draw, I would like the window to be completely "blank" (A.K.A  no menu or title bar, etc.)  I only want what I draw to be displayed.  Ultimately, the app should be able to destroy the window using something like:

DestroyWindow(myNewSampleWindowHWND)

Does that make sense?  I know how to do this in VC++, but am trying to stick to C# for code-management purposes.  I have tried and tried to no avail to get this to work in C#, and I could really use some help.

Thanks so much!!!
Kendell
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Question by:kwelch007
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It turns out that, for my purposes at least, I was able to create a topmost/"transparent" window using the VS2008 wizard.  I created a Form, set its FormBorderStyle to "none", set its TopMost property to "true", and set both its BackColor and TransparencyKey values to the same color.  It then became useable for my purposes.

It seems to me that nobody on the web has published any working code using API calls to RegisterClassEx and CreateWindowEx (including the WNDCLASSEX structure.)  I can still think of a lot of reasons that someone might need to use RegisterClassEx and CreateWindowEx directly from C#, and I hope this thread continues.

I would also note that the .NET "NativeWindow()" function might be useful, but I had trouble with the MSDN sample code conflicting with another class I was using, and came across my solution before pursuing the problem.

Thanks anyway!
Kendell
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