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Aardvajk

Win32 API "EDIT" controls

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Probably a bit of a dopey question, but if I create an edit control with the C Win32 API: HWND Edit=CreateWindow("EDIT","",WS_CHILD, ... etc How would I go about intercepting keystrokes made when typing in that control so that I can do special processing? I'm tring to put a borderless edit control on top of a grid to implement property editing and want to move the edit box up or down when the appropriate arrow keys are pressed but I can't find anything in the docs about custom responding to keypresses. Thanks. [EDIT] I've just been reading about sub-classing, i.e. providing a custom WndProc for the edit control and deferring any messages I don't process to the original WndProc for the control. Is that the simplest way to do what I want, does anyone know?

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Yes, this is the most proper way of doing it and it is fairly simple (maybe not for the first time). In fact, it is commonly used for other control too ;-)

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Yup, I agree that subclassing the window is the easiest way. From my code (For a RichEdit, but same thing really):

// Bloody Microsoft headers
#ifdef _WIN64
# define CAST_TYPE (LONG_PTR)
#else
# define CAST_TYPE (LONG)(LONG_PTR)
#endif

// Create window
m_hWnd = CreateWindowEx(WS_EX_TRANSPARENT, RICHEDIT_CLASS, "", dwFlags, x, y, w, h, hWndParent,
NULL, hInstance, NULL);
if(!m_hWnd)
return false;
SetWindowLongPtr(m_hWnd, GWLP_USERDATA, CAST_TYPE this);

// Subclass RichEdit
m_pfnOldProc = (WNDPROC)(LONG_PTR)GetWindowLongPtr(m_hWnd, GWLP_WNDPROC);
SetWindowLongPtr(m_hWnd, GWLP_WNDPROC, CAST_TYPE CDruinkEdit::StaticWindowProc);

// Snip...

LRESULT CALLBACK CDruinkEdit::StaticWindowProc(HWND hWnd, UINT uMsg, WPARAM wParam, LPARAM lParam)
{
CDruinkEdit* pParent;

pParent = (CDruinkEdit*)(LONG_PTR)GetWindowLongPtr(hWnd, GWLP_USERDATA);
if(!pParent) return DefWindowProc(hWnd, uMsg, wParam, lParam);
return pParent->WindowProc(uMsg, wParam, lParam);
}

LRESULT CDruinkEdit::WindowProc(UINT uMsg, WPARAM wParam, LPARAM lParam)
{
switch(uMsg)
{
case WM_DESTROY:
OnDestroy();
break;

// Snip...
}
return m_pfnOldProc(m_hWnd, uMsg, wParam, lParam);
}

void CDruinkEdit::OnDestroy()
{
SetWindowLongPtr(m_hWnd, GWLP_WNDPROC, CAST_TYPE m_pfnOldProc);
SetWindowLongPtr(m_hWnd, GWLP_USERDATA, 0);
}



The reason for that CAST_TYPE mess is to get the code to compile correctly and without warnings in both x86 and x64 configurations. The MS headers seem to make that particularly difficult...

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Cheers Steve.

I note that when you handle the WM_DESTROY message, you then break out and still call the original handler. Do you have to do that for all messages? If I want to override a keypress, is it good practise to just return from my Proc without calling the original or should I modify the keycode in the message (to zero or something) and hand it on to the default Proc?

I'll play around and see what happens either way but just wondered what people thought. Cheers for the code though.

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Quote:
Original post by EasilyConfused
Cheers Steve.

I note that when you handle the WM_DESTROY message, you then break out and still call the original handler. Do you have to do that for all messages? If I want to override a keypress, is it good practise to just return from my Proc without calling the original or should I modify the keycode in the message (to zero or something) and hand it on to the default Proc?

I'll play around and see what happens either way but just wondered what people thought. Cheers for the code though.
Yes, you should pass all messages off to the original handler, otherwise the control won't behave like an Edit control unless you override all the relevant messages. For keystrokes, I don't think it'll be nessecary to pass them to the original handler, unless you want the key to be typed. I wouldn't change the keystroke message then pass it on.

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Just got it all implemented and all works like a dream. Really handy new thing to know about, this subclassing stuff.

Thanks all.

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