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Create MDI child from dll

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I've been developing a control which combines a MDI Client and a Tab Control, one similar to the one VS uses. After writing it as a regular project I decided to write it as a dll to make it easier to use in future projects. The dll creates a MDI Client and a Tab Control in the parent window, but when I'm calling CreateMDIWindow the HWND is NULL and GetLastError returns 8 (ERROR_NOT_ENOUGH_MEMORY). The call for CreateMDIWindow is made within the dll. What's wrong?! Appreciate any comments! / Olle Häggdahl

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Here's the whole Add function!
Hope it'll help.

void CMDITabControl::AddItem(LPSTR lpWndTitle)
HWND hWndChild;
CWnd *wnd = NULL;

wnd = new CWnd;

hWndChild = CreateMDIWindow(
0, 0, 0, 0,

MessageBox(m_hWndWorkspace, "Child window creation failed!", "MDITabControl Error!", MB_ERROR);

// Show the tab control if it was previously hidden
if(m_nSize == 0)
ShowWindow(m_hWndTab, SW_SHOW);
ShowWindow(m_CloseBtn.m_hWnd, SW_SHOW);

// Add to our tab control
ti.mask = TCIF_TEXT;
ti.pszText = lpWndTitle;

SendMessage(m_hWndTab, TCM_INSERTITEM, 0, (LPARAM)(LPTCITEM)&ti);
SendMessage(m_hWndTab, TCM_SETCURSEL, 0, 0);

// Insert in our window list and increase size
wnd->m_hWnd = hWndChild;
wnd->m_pNext = m_pFirst;
m_pFirst = wnd;

[Edited by - Haggdahl on October 22, 2006 2:10:39 PM]

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Edit your post to use [ source ] [ /source ] tags.

Are you sure that the parameters to CreateMDIWindow() are correct? Where are you getting m_hInstWorkspace?

Also, for style and clarity, I recommend you use CW_USEDEFAULT rather than zeros if you want the default size and position.

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Thanks for the advice with tags!

As you can see the window is maximized and will stay maximized as long as it's visible, so the zeros doesn't matter.
The m_hInstWorkspace is defined in Init(), which is given the HINSTANCE from the parent when called. But I recently discovered that the HINSTANCES shouldn't matter
because their value is, almost always, 0x00400000. (some standard in Win32, see "http://blogs.msdn.com/oldnewthing/archive/2006/05/05/590749.aspx" which says some concerning Win32 and HINSTANCES)
And the rest of the parameters should be all right. This is very confusing.

/ Olle

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I've got it now. Skipped registering the class in the dll and now it works. Don't really know what was wrong. Thanks anyway!

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