Edit Controls in MDI Child

Ajay P Sathe -- apsathe@giaspn01.vsnl.net.in
Monday, April 15, 1996

Problem :  
Edit controls invisible in a MDI Child window, on increasing stacksize.
Other controls work OK.


Environment : VC++ 1.52, Windows 3.1

Other params : 
1. OLE controls enabled.
2. VBX controls disabled.
3. Local heap size is set to MAXVAL in .DEF file.

- App is spread over 50 programs - other than MFC Library.
- MFC Library is statically linked.
- Linking Environment needs minimum 200 segments.
- Memory Model : Large

I have a MDI child window. In OnCreate() I have created 3 edit controls,
3 combo box controls, 5 bitmap buttons, 1 listbox.

If I set stacksize limit to 16k bytes as it is needed for our application,
then the 3 edit controls vanish, but other controls do appear.

Instead, if I set stacksize 12k then the edit controls become visible. But 
then the App is not stable, because it really does require a greater stacksize.
So, with this kind of random reduction, the App malfunctions at random
places.

What's going wrong ? Is there inadequate heap space ? How do I increase it ? 
Or how do I reduce my App's demand on heap space ?

Observation : MFC's edit-control create fails with return value indicating
              that WINDOWS edit-control create itself failed. 

Window create parameters are correct. When the problem occurs, if I try 
to open a dialog box, which has 5 edit controls, those edit controls 
are visible.

What I need help on is :
1. Different reasons that can cause this type of problem (Is it something to
   with memory management ?)
2. How to solve this. 

TIA

- Ajay Sathe, Spectrum

---

Graeme Hibbert -- graeme@grover.delphic.co.nz
Friday, April 19, 1996

Ajay P Sathe wrote:

> 
> Problem :
> Edit controls invisible in a MDI Child window, on increasing stacksize.
> Other controls work OK.
> 
> Environment : VC++ 1.52, Windows 3.1
> 
> Other params :
> 1. OLE controls enabled.
> 2. VBX controls disabled.
> 3. Local heap size is set to MAXVAL in .DEF file.
> 
> - App is spread over 50 programs - other than MFC Library.
> - MFC Library is statically linked.
> - Linking Environment needs minimum 200 segments.
> - Memory Model : Large
> 
> I have a MDI child window. In OnCreate() I have created 3 edit controls,
> 3 combo box controls, 5 bitmap buttons, 1 listbox.
> 
> If I set stacksize limit to 16k bytes as it is needed for our application,
> then the 3 edit controls vanish, but other controls do appear.
> 
> Instead, if I set stacksize 12k then the edit controls become visible. But
> then the App is not stable, because it really does require a greater stacksize.
> So, with this kind of random reduction, the App malfunctions at random
> places.
> 
> What's going wrong ? Is there inadequate heap space ? How do I increase it ?
> Or how do I reduce my App's demand on heap space ?
> 
> Observation : MFC's edit-control create fails with return value indicating
>               that WINDOWS edit-control create itself failed.
> 
> Window create parameters are correct. When the problem occurs, if I try
> to open a dialog box, which has 5 edit controls, those edit controls
> are visible.
> 
> What I need help on is :
> 1. Different reasons that can cause this type of problem (Is it something to
>    with memory management ?)
> 2. How to solve this.
> 
> TIA
> 
> - Ajay Sathe, Spectrum

I had a similar problem where edit controls would fail to create themselves
but my problem was more related to the large numbers of edit controls I required.
Up to 200+ on any particular MDI child.

I solved this by allocating memory for them off the Global heap after the local
heap was exhausted; in the derived create function. Basically the code looks
something like this:

BOOL CMyEdit::Create(DWORD dwStyle, const RECT& rect, CWnd* pParent, UINT nID)
{
	// Local heap edits ............
	if ( CEdit::Create(dwStyle, rect, pParent, nID) )
		return( TRUE );

        // Global Heap Edits if the local heap is exhausted.
	// Attempt to allocate memory for the edits from the global heap
	HWND hWnd;

	hEditDS = (HINSTANCE)::GlobalAlloc( GMEM_MOVEABLE | GMEM_ZEROINIT | GMEM_SHARE, 256L );
	if (hEditDS == NULL) {
		// Allocation failed
		return( FALSE );
	}
   
	// Create the edit control.
	// Pass the local heap handle in hInstance.
	if ( ( hWnd = ::CreateWindow( "edit", NULL, dwStyle, rect.left, rect.top, rect.right - rect.left, 
			rect.bottom - rect.top, pParent->GetSafeHwnd(), (HMENU)nID, hEditDS, NULL) ) == NULL )
		return( FALSE );

	if ( !Attach( hWnd ) )
		return( FALSE );

	if ( !SubclassWindow( hWnd ) )
		return( FALSE );

	return( TRUE );
}

I hold the hEditDS handle in the instance of the Edit control so I can GlobalFree
it later. There is a Technical Articlw on Edits which explains it better simply 
called "Edit Controls" by Kyle Marsh Microsoft Developer Network Technology Group
on the MSDN CD.

Since you seem to be juggling the local resources this may or may not help you, 
but its a suggestion.

Cheers
Graeme Hibbert

======================================================================================
Delphic Medical Systems Ltd.
Auckland, New Zealand
======================================================================================

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