Doug Kavendek Doug Kavendek - 1 month ago 15
C++ Question

Problems with setting application icon

(I'm using Visual Studio 2008, though I remember having similar problems with older versions as well.)

I've tried several different methods (many of them mentioned in this other question), but I am still having some strange issues:


  1. When including an icon as a resource, it does show up as the executable file's icon immediately, but for the icon to show up on the taskbar, I have to restart the computer. Until then, it continues to show up as whatever the previous icon was. Cleaning the solution, restarting VS, doesn't have any effect. Not a really big issue, as it won't affect a released exe, but it would be nice to know where it's keeping the old icon cached and how to get rid of it.

  2. No matter what I do, the icon displayed when alt-tabbing is the default app icon (square and white and generic). This includes embedding the icon in the executable, as well as setting
    ICON_BIG
    with
    WM_SETICON
    .



As for the second matter, my code looks something like:

hIcon = (HICON)(
LoadImage( NULL, szFilename, IMAGE_ICON, 32, 32, LR_LOADFROMFILE ) );
if( hIcon )
SendMessage( hWnd, WM_SETICON, ICON_BIG, (LPARAM)hIcon );


However, after sending
WM_SETICON
,
GetLastError()
returns 6, "The handle is invalid.".
hWnd
is a valid window handle, and
hIcon
appears to be a valid icon handle. I've tried searching for reasons why
WM_SETICON
could cause that error, and at the very least, to figure out WHICH handle it thinks is invalid, but no luck yet. I've cleared the error code immediately before calling
SendMessage()
, so it has to be set somewhere in the processing of the message.

I tried an alternate method, loading the icon from the exe itself, where the ID of the resource is
101
(it's the first and only resource included):

hIcon = (HICON)(
LoadImage( GetModuleHandle( NULL ), MAKEINTRESOURCE( 101 ),
IMAGE_ICON, 48, 48, 0 ) );
if( hIcon )
SendMessage( hWnd, WM_SETICON, ICON_BIG, (LPARAM)hIcon );


... but the same thing happens; after calling
SendMessage()
,
GetLastError()
gives the same error status.

I've tried different dimensions (such as 48x48, all of which are present in the icon file), but to no different effect. I know it's definitely finding and loading the images, because if I specify a size that doesn't exist or an invalid resource ID or the wrong filename (depending on how I am loading it), it fails out long before
SendMessage()
.

Strangely, if I specify
ICON_SMALL
instead of
ICON_BIG
, the call succeeds with no error status, but from the docs, I need to use
ICON_BIG
to set the icon used while alt-tabbing. Also, if I use
ICON_BIG
but load the 16x16 icon, I get no error status, but nothing changes.

Any ideas about what could be causing
WM_SETICON
to fail? Anything terribly wrong with any of the code I've posted (aside from formatting/style/casting issues, as it's simplified to just the basics)?

Answer

I've revisited this to see if I can close out my question. I have been unable to get the app's icon to show up in the alt-tab list just through embedding it in the executable; it will show up in the taskbar, as the file's icon in Explorer, and elsewhere just fine.

I figured I'd try something simpler for setting the icon manually, and went with LoadIcon() instead, as the code below shows:

HICON hIcon = LoadIcon( GetModuleHandle(NULL), MAKEINTRESOURCE(IDI_ICON1) );
if( hIcon )
{
   SendMessage( GetHandle(), WM_SETICON, ICON_BIG, (LPARAM)hIcon );
   DestroyIcon( hIcon );
}
// ... Same for ICON_SMALL

This seems to have done the trick. I really don't know why, but so far it's the only change that had any effect. It's really not an issue I should spend any more time on, so I'll just go with this.