CMPT 212 Object-Oriented Applications Design in C++ Spring 1998

The WM_PAINT Message (continued)

• Your application sends a WM_PAINT message to a window by using the InvalidateRect function.

     InvalidateRec(hwnd, NULL, 1);
  	 

  • The first parameter is the handle of the window that is to receive the WM_PAINT message.

  • The second parameter is a pointer to a RECT structure which describes the rectangle within the window that should be painted. Passing NULL requests that the entire window be painted.

  • The third parameter specifies whether or not the background should be erased before painting.

• Your application will typically need to store its data in variables accessible by different functions (eg. module variables) because the functions which update the data cannot pass the data to the function which uses the data to paint the window.

Message Boxes

• Message boxes are windows that display a message and wait for an acknowledgement.

• Message boxes normally have buttons which allow the user to respond in certain ways:
  • Abort, Retry, Ignore
  • Yes, No
  • OK
  • OK, Cancel
  • and others.

• Message boxes are created and displayed using the function

     int MessageBox(HWND, LPCSTR, LPCSTR, UINT)
  	 

  where
  • HWND is the handle of the parent window,
  • the first LPCSTR is a pointer to the message string,
  • the second LPCSTR is a pointer to the caption string,
  • UINT specifies the types of buttons and icons to display,
  • the return value specifies how the user responded.

• Example: Here is some code that will product this message box:
  

     int response;
  
     response = MessageBox(hwnd, "What now?", "Question", 
                           MB_OKCANCEL | MB_ICONQUESTION);
  
     switch (response) {
  
        case IDOK:
  	 ...   // user pressed "OK" button.
  	 break;
  
        case IDCANCEL:
  	 ...   // user pressed "Cancel" button.
  	 break;
  
        }
  	 

Resource Files

• Resources are items which are used in your program, but are defined outside of your program.

• Resources include:
  • menus,
  • icons,
  • dialog boxes,
  • bitmapped graphics.

• Resources are defined in a .rc file using a scripting language.
  • They are compiled into a .res file using a resource compiler (typically rc.exe).

  • The .res file is then linked into your .exe file by the linker.

• You may edit the .rc resource file by hand using a text editor, or by a resource editor such as the Borland Resource Editor.

Menus

• Menus are defined in the resource file.

• There are two types of menu items:
  1. popup submenus,
  2. final selections.

• Suppose we want to define this menu:

• Here is what the .rc file would contain:

     #include "menu.h"
  
     MYMENU MENU
     {
        POPUP "&File"
        {
  	 MENUITEM "&Open",  IDM_OPEN
  	 MENUITEM "&Close", IDM_CLOSE
  	 MENUITEM "&Quit",  IDM_QUIT
        }
        POPUP "&Edit"
        {
  	 MENUITEM "Cop&y",  IDM_COPY
  	 MENUITEM "&Paste", IDM_PASTE
        }
        MENUITEM "&Help",     IDM_HELP
     }
  	 

  • MYMENU is the name of the menu. Your application will use this name to specify to MS-Windows what menu it wants to use.

  • The IDM_ names refer to constants defined in your file menu.h. Your .cpp file will include menu.h because the IDM_ values are values passed to your application by MS-Windows when the user chooses items from the menu.

  • The & in the item string causes MS-Windows to underline that letter. The user can then press the letter to select the item instead of using the mouse. The letter is called the shortcut key.

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