DOCUMENT:Q29733  17-JUN-1999  [win16sdk]
TITLE   :HOWTO: Drawing a Different Icon for Each Application Instance
PRODUCT :Microsoft Windows Software Development Kit
PROD/VER:WINDOWS:3.1
OPER/SYS:
KEYWORDS:kb16bitonly kbSDKWin16

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3.00 3.10
WINDOWS
kbprg

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The information in this article applies to:

 - Microsoft Windows Software Development Kit (SDK) 3.1 
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SUMMARY
=======

An application can use the DrawIcon function in its paint procedure to display a
different icon for each application instance. The method has the following five
steps.

MORE INFORMATION
================

1. In the WNDCLASS data structure used to register the application's main window
   class, set the hIcon field to NULL. This prevents Windows from drawing an
   icon when the application is minimized. The following code demonstrates this
   step:

      int index;  // global variable to count application instances

      // This function initializes the first application instance
      void InitFirst(HANDLE hInstance)
      {
         WNDCLASS rClass;            // window class structure

         rClass.lpszClassName = "HELLO";
         rClass.hInstance     = hInstance;
         rClass.lpfnWndProc   = WindowProc;
         rClass.hCursor       = LoadCursor(NULL, IDC_ARROW);

         // If hIcon is NULL, Windows will not draw icon. Application
         // paints its own icon as appropriate.
         rClass.hIcon         = NULL;

         rClass.lpszMenuName  = NULL;
         rClass.hbrBackground = COLOR_WINDOW + 1;
         rClass.style         = CS_HREDRAW | CS_VREDRAW;
         rClass.cbClsExtra    = 0;
         rClass.cbWndExtra    = 0;

         RegisterClass(&rClass);     //  register the class

         index = 1;  // set counter to indicate first instance
      }

2. The GetInstanceData function provides the value of the instance counter from
   the previous instance. Adding one to this value provides the value for the
   current instance, as follows:

      void InitNext(HANDLE hInstance, HANDLE hPrevInstance)
      {
         GetInstanceData(hPrevInstance, (PSTR)&index, sizeof(int));
         index++;
      }

3. During the instance initialization function, load the icon for the current
   instance from the application's resources. In this case, Icon1, Icon2, Icon3,
   and Icon4 are individual icons declared in the application's resources. The
   following code demonstrates this procedure:

      HICON hIcon; // icon handle for this instance

      void InitEvery(HANDLE hInstance, int cmdShow)
      {
         HWND  hWnd;

         hInst = hInstance; // store instance in global variable for
                            // window procedures to use

         switch (index)
            {
         case 1: hIcon = LoadIcon(hInstance, "Icon1");
                 break;

         case 2: hIcon = LoadIcon(hInstance, "Icon2");
                 break;

         case 3: hIcon = LoadIcon(hInstance, "Icon3");
                 break;

         default:
                 hIcon = LoadIcon(hInstance, "Icon4");
            }

         CreateWindow( ... ); // and so forth
      }

4. When an application receives a WM_PAINT message while the window is
   minimized, draw the icon in the application's client area. The IsIconic
   function returns TRUE if the application is minimized. The following code
   demonstrates this step:

      // In the switch(message) statement of the main window procedure

      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 in the cleared area
            DrawIcon(ps.hdc, 0, 0, hIcon);

            EndPaint(hWnd, (LPPAINTSTRUCT)&ps);
            }
         else
            // Paint the window as usual
         }

5. When the user drags an application's icon with the mouse and the application
   processes the WM_QUERYDRAGICON message as follows, Windows changes the mouse
   cursor to a black-and-white representation of the application's icon.

      // In the switch(message) statement of the main window procedure

      case WM_QUERYDRAGICON:
         return (LONG)(WORD)hIcon;
         break;

Additional query words: 3.00 3.10

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Keywords          : kb16bitonly kbSDKWin16 
Technology        : kbAudDeveloper kbWin3xSearch kbSDKSearch kbWinSDKSearch kbWinSDK310
Version           : WINDOWS:3.1
Issue type        : kbhowto

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