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CWnd::GetIcon won't work

Posted on 1998-09-21
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Last Modified: 2013-11-19
I have this chunk of code in my app
      if (hicon == NULL) {
            CWnd * p_wnd = AfxGetMainWnd();
            if (p_wnd != NULL)
                  hicon = p_wnd->GetIcon(TRUE);
      }

I traced it to the GetIcon call. It returns NULL.  However, I use the m_hWnd member of p_wnd in SPY++ and the properties show me an icon handle.  I know the icon handle is correct because I then used the debugging tools to plug in that icon handle (replacing the NULL) and it used the correct icon.

What am I doing wrong?  How do I get this call to work?
Is there an alternate way of doing this?
Danny Pav
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Question by:danny_pav
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10 Comments
 
LVL 1

Expert Comment

by:Bonev
ID: 1322386
Try p_wnd->GetIcon(FALSE);

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LVL 1

Expert Comment

by:Bonev
ID: 1322387
Try p_wnd->GetIcon(FALSE);

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LVL 1

Expert Comment

by:Bonev
ID: 1322388
In your CMainFrame::Create you will need to set the icon for that window.

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Author Comment

by:danny_pav
ID: 1322389
Bonev:
That can't be right.  The correct icon is already displaying and from my original problem statement:

However, I use the m_hWnd member of p_wnd in SPY++ and the    properties show me an icon handle.  I know the icon handle is correct because I then used the debugging tools to plug in that icon handle (replacing the NULL) and it used the correct icon.

SPY++ recognizes the icon.  Why does that function fail?
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LVL 1

Expert Comment

by:Bonev
ID: 1322390
danny_pav,
I wrote a sample app and I've run into the same problem.
When I put a SetIcon call in CMainFrame::Create everything went fine.
Basically, there are several things to do:
1. In InitInstance:
Check if the main frame is created and assigned to m_pMainWnd
2. In CMainFrame::Create:
call SetIcon(hIcon, FALSE); // if you need a big icon, use TRUE
3. In your function:
call GetIcon(FALSE); // the size should be the same as in 2


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LVL 3

Author Comment

by:danny_pav
ID: 1322391
Why do I have to do a SetIcon when the icon is already set?  I can look at the screen to verify and I can use SPY to verify.
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LVL 1

Expert Comment

by:Bonev
ID: 1322392
Sure you need to set it - you cannot force the user to put the handle manually.

0
 
LVL 8

Accepted Solution

by:
Answers2000 earned 200 total points
ID: 1322393
The default Icon is associated with the class not the window (windows looks for a window icon first, then if it doesn't find one then looks for a class icon).

Bonev's work round works, because it sets the window icon (rather than the window class icon) so WM_GETICON will see it.

To fix generically, you don't need to set the icon, do:

if (hicon == NULL)
{
CWnd * p_wnd = AfxGetMainWnd();

// look for window icon
if (p_wnd != NULL)
  hicon = p_wnd->GetIcon(TRUE);

// look for class icon if no window icon found
if ( (hicon == NULL ) && ( p_wnd != NULL ) )
  hicon = (HICON)::GetClassLong( p_wnd->m_hWnd, GCL_HICON ) ;
}
0
 
LVL 3

Author Comment

by:danny_pav
ID: 1322394
I didn't think that would work with MFC.  I figured that a only a few stock window classes were used and that would include stock icons as well (if any).  

I still don't understand why GetIcon or WM_GETICON doesn't work.  It seems to be not just a shortcoming of MFC.  

Thanks, Bonev for the effort.
Thanks, Answers2000 for the answer.
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LVL 8

Expert Comment

by:Answers2000
ID: 1322395
>> I didn't think that would work with MFC. 
I don't see why not

>> I figured that a only a few stock window classes were used and that would include stock icons as well (if any).  
I was _strongly_ under the impression that MFC 4.2 generates strings and registers _multiple_ window classes (re-using same WndProcs).  Older versions (I think) re-use the same classes.
You can read the sources and check on whichever MFC version you're using...Search for RegisterClass

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