SAMPLE: Implementing a Read-Only Edit Control In Windows

• Microsoft Windows Software Development Kit (SDK) for Windows versions 3.0 and 3.1

SUMMARY

In some situations, an application may contain text that is displayed for the user to read, which is undesirable for the user to modify. The application can use a static control to contain this text if the message is short. However, for larger amounts of text, which require scrolling to display all the text in the allotted area, something closer to an edit control is required. This article, and its associated sample code, details how to make an edit control "read- only."

ROEDIT is a file in the Microsoft Software Library that demonstrates the techniques discussed in this article.

Download ROEDIT.EXE, a self-extracting file, from the Microsoft Software Library (MSL) on the following services:

• Microsoft Download Service (MSDL)

        Dial (206) 936-6735 to connect to MSDL
        Download ROEDIT.EXE (size: 23594 bytes) 
  

• Internet (anonymous FTP)

        ftp ftp.microsoft.com
        Change to the \SOFTLIB\MSLFILES directory
        Get ROEDIT.EXE (size: 23594 bytes) 
  

MORE INFORMATION

An application can create a read-only edit control by subclassing or superclassing a standard edit control. The subclass procedure filters out messages that change the contents of the edit control. The following code fragment demonstrates this process:

   FARPROC gOldProc;

   LONG FAR PASCAL ROEditProc(HWND hWnd, WORD msg,
                              WORD wParam, LONG lParam)
   {
       switch (msg)
       {
           case WM_KEYUP:
           case WM_KEYDOWN:
           case WM_CHAR:
           case WM_CUT:
           case WM_COPY:
           case WM_PASTE:
           case WM_LBUTTONUP:
           case WM_LBUTTONDOWN:
           case WM_LBUTTONDBLCLK:
               return 1L;

           case WM_GETDLGCODE:
               return 0L;
       }

       return CallWindowProc(gOldProc, hWnd, msg, wParam, lParam);
   } //*** ROEditProc

The following example demonstrates superclassing an edit control to create a new ROEDIT-class control that behaves similar to a read-only edit control. A ROEDIT control implements the window procedure provided above. It also changes the cursor to an arrow instead of an I-beam, which provides an additional indication to the user that the contents of the control cannot be changed. Using an ROEDIT control eliminates the necessity of subclassing each control after it is created. When the application creates a control from the ROEDIT class, the read-only behavior is provided automatically.

The following code demonstrates superclassing an edit control as described above:

   FARPROC gOldProc;

   BOOL RegisterROEdit(HANDLE hInstance)
   {
       WNDCLASS wc;

       if (!GetClassInfo(NULL, "EDIT", &wc))
           return FALSE;

       gOldProc = (FARPROC)wc.lpfnWndProc;

       wc.style        &= ~CS_GLOBALCLASS;
       wc.lpfnWndProc   = ROEditProc;
       wc.hInstance     = hInstance;
       wc.hCursor       = LoadCursor(NULL, IDC_ARROW);
       wc.lpszClassName = "ROEDIT";

       return RegisterClass(&wc);

   } //*** RegisterROEdit