Q29733: HOWTO: Drawing a Different Icon for Each Application Instance

Article: Q29733
Product(s): Microsoft Windows Software Development Kit
Version(s): WINDOWS:3.1
Operating System(s): 
Keyword(s): kb16bitonly kbSDKWin16
Last Modified: 17-JUN-1999

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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