ID Number: Q74539
3.00 3.10
WINDOWS
Summary:
The text below describes how an application developed for the
Microsoft Windows graphical environment can draw its own icon when it
is minimized. An application can use these techniques to draw
different icons to indicate its state.
In Windows version 3.1, an application can initiate a dynamic data
exchange (DDE) conversation with the Windows Program Manager to
determine which icon the user has associated with an application and
can then draw that icon using the following techniques.
More Information:
To draw its own icon when minimized, a Windows application performs
the following five steps:
1. When the application registers its main window's window class,
specify NULL as the value of the hIcon member of the WNDCLASS data
structure.
2. Create a static variable to store the icon the application will
use, as follows:
HICON hIcon;
Initialize this variable to the value returned from the CreateIcon
or LoadIcon function.
3. To draw the icon, process the WM_PAINT message in the main window's
window procedure as follows:
case WM_PAINT:
{
PAINTSTRUCT ps;
if (IsIconic(hWnd))
{
BeginPaint(hWnd, (LPPAINTSTRUCT)&ps);
// Paint the desktop window background.
DefWindowProc(hWnd, WM_ICONERASEBKGND, (WORD)ps.hdc, 0L);
// Draw the icon on top of it.
DrawIcon(ps.hdc, 0,0, hIcon);
EndPaint(hWnd, (LPPAINTSTRUCT)&ps);
}
else
return DefWindowProc(hWnd, message, wParam, lParam);
}
4. To prevent a screen flash when the application draws the icon,
process the WM_ERASEBKGND message in the main window's window
procedure, as follows:
case WM_ERASEBKGND:
if (IsIconic(hWnd))
// Do not erase the background now. When the application
// paints its icon, it will erase the background.
return TRUE;
else
return DefWindowProc(hWnd, message, wParam, lParam);
5. Process the WM_QUERYDRAGICON message in the main window's window
procedure. When the user is about to drag a window that has no icon
defined for its window class, Windows sends it a WM_QUERYDRAGICON
message. The code below causes Windows to create a dragging cursor
based on the specified icon. Windows automatically converts a color
icon to a monochrome cursor.
case WM_QUERYDRAGICON:
return (LONG)(WORD)hIcon;
break;
Additional reference words: 3.00 3.10