Multiple subclassing in SDK ...

Posted on 2001-08-16
Last Modified: 2008-03-17

I'm writing a Windows SDK application (no MFC). It is a dialog box based app with 5 controls - 2 textbox controls, 2 buttons and 1 ListView control. I want to handle the key strokes on both the text boxes - which is possible by subclassing. The problem I am facing is that I'm able to subclass only one of the text box control. Here is a portion of my code:

WNDPROC fnOldProc;

BOOL WINAPI WinMain (HINSTANCE hInst, HINSTANCE hPrevInst, LPSTR lpCmdLine, int nShowCmd)
        HWND hDlg = 0;
     MSG msg = {0};
     hDlg = CreateDialog (hInstance, MAKEINTRESOURCE
        (IDD_SEARCHDLG), 0, (DLGPROC)SearchDlgProc);
     if (hDlg == 0)
          MessageBox (0, "Unable to Initialize
                Search Box", "Error", MB_OK);
          return -1;

     ShowWindow (hDlg, SW_SHOW);
     UpdateWindow (hDlg);
     while (GetMessage (&msg, hDlg ,0, 0) > 0  )
           if (hDlg == 0 || !IsDialogMessage (hDlg, &msg))
     return msg.wParam;

/* call back function for the dialog box */
BOOL CALLBACK SearchDlgProc (HWND hWnd, UINT msg,
WPARAM wParam, LPARAM lParam)
    switch (msg)
     case WM_INITDIALOG:
            HWND hText1;
            hText1 = GetDlgItem(hWnd, IDC_TEXT1);
            fnOldProc = (WNDPROC) SetWindowLong(hText1,
            GWL_WNDPROC, (LONG)Text1Proc);
            return TRUE;
    return FALSE;

/* call back function for IDC_TEXT1 */
BOOL CALLBACK Text1Proc (HWND hWnd, UINT msg, WPARAM wParam, LPARAM lParam)
     switch (msg)
     case WM_CHAR:
          /* handle key strokes */
     return CallWindowProc (fnOldProc, hWnd, msg,
        wParam, lParam);

When the dialog box initializes, the IDC_TEXT1 gets subclassed. Now, how do I handle the key strokes for IDC_TEXT2 - where do I add the subclassing code for the IDC_TEXT2? I have the call back function ready.

Question by:smnaha
Welcome to Experts Exchange

Add your voice to the tech community where 5M+ people just like you are talking about what matters.

  • Help others & share knowledge
  • Earn cash & points
  • Learn & ask questions
LVL 31

Accepted Solution

Zoppo earned 150 total points
ID: 6396433
Hi smnaha,

simply do it at the same place and in the same manner as you do it for IDC_TEXT1, i.e.:

   HWND hText1;
   hText1 = GetDlgItem(hWnd, IDC_TEXT1);
   fnOldProc = (WNDPROC) SetWindowLong(hText1, GWL_WNDPROC, (LONG)Text1Proc);
   HWND hText2 = GetDlgItem( hWnd, IDC_TEXT2 );
   fnOldProc2 = (WNDPROC) SetWindowLong( hText2, GWL_WNDPROC, (LONG)Text2Proc);
   return TRUE;
hope that helps,

LVL 49

Expert Comment

ID: 6405361
One way is to have subclassed window proc handle both edit boxes:

WNDPROC afnOldProc[2];
    int nRsrcID= GetWindowLong( hWnd, GWL_ID );
    WNDPROC fnOldProc;
    if ( nRsrcID == IDC_EDIT1 ) fnOldProc= afnOldProc[0];
    if ( nRsrcID == IDC_EDIT2 ) fnOldProc= afnOldProc[1];

    switch (msg) {
        case WM_CHAR:
            if ( nRsrcID == IDC_EDIT1 ) {
                AfxMessageBox("hi from edit box 1");
            if ( nRsrcID == IDC_EDIT2 ) {
                AfxMessageBox("hi from edit box 2");
    return CallWindowProc (fnOldProc, hWnd, msg, wParam, lParam );

=-=-=-=-=-=-=- in WM_INITDIALOG handler
    HWND hwndEdit;
    hwndEdit= ::GetDlgItem(m_hDlg, IDC_EDIT1);
    afnOldProc[0]= (WNDPROC)SetWindowLong( hwndEdit, GWL_WNDPROC, (LONG)MyEdProc);
    hwndEdit= ::GetDlgItem(m_hDlg, IDC_EDIT2);
    afnOldProc[1]= (WNDPROC)SetWindowLong( hwndEdit, GWL_WNDPROC, (LONG)MyEdProc );

The key to reusing the same subclassing fn is...
    int nRsrcID= GetWindowLong( hWnd, GWL_ID );

That obtains the identifier of the edit control so you can do different things depending upon which edit control is being handled.

-- Dan

Author Comment

ID: 6412152
Thanks a lot. Dan Rollins comments were also useful.

Featured Post

Independent Software Vendors: We Want Your Opinion

We value your feedback.

Take our survey and automatically be enter to win anyone of the following:
Yeti Cooler, Amazon eGift Card, and Movie eGift Card!

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Introduction This article is a continuation of the C/C++ Visual Studio Express debugger series. Part 1 provided a quick start guide in using the debugger. Part 2 focused on additional topics in breakpoints. As your assignments become a little more …
Basic understanding on "OO- Object Orientation" is needed for designing a logical solution to solve a problem. Basic OOAD is a prerequisite for a coder to ensure that they follow the basic design of OO. This would help developers to understand the b…
The goal of the video will be to teach the user the concept of local variables and scope. An example of a locally defined variable will be given as well as an explanation of what scope is in C++. The local variable and concept of scope will be relat…
The viewer will learn additional member functions of the vector class. Specifically, the capacity and swap member functions will be introduced.

622 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question