Validating Tree/List Control In-Place Edit

Introduction

Ever wanted to edit tree or list control labels, and include text validation as you type? I searched a lot of places for such methods of validating text while typing in the label edit control of a tree or list control on an MFC dialog. I could only find complicated custom classes and the like, most of which had far more functionality than I was after.

Method

I implemented something very simple in the dialog PreTranslateMessage method (use the Class Wizard to add this method to your dialog code). Whether the following code is useful to you depends on the complexity of the validation you require. I was only interested in restricting input, so this works very well.

BOOL CCMyDialog::PreTranslateMessage(MSG* pMsg)
{
    //----------------
    // Local variables
    //----------------

    CString strEditIn = "";
    CString strEditOut = "";
    TCHAR c;

    //------------------------------
    // Get the window with the focus
    //------------------------------

    CWnd *pCont = GetFocus();

    //--------------------------------
    // Get list (or tree) edit control
    //--------------------------------
    
    CEdit *pEdit = m_ListCtrl.GetEditControl();
    //CEdit *pEdit = m_TreeCtrl.GetEditControl();

    //----------------------------------------------------
    // Only proceed if the edit control exists and has 
    // the focus
    //----------------------------------------------------

    if (pCont == pEdit)
    {
        switch(pMsg->message)
        {
            //----------------------------
            // Catch the character message
            //----------------------------

            case WM_CHAR:
            switch(pMsg->wParam)
            {
                //-----------------------------
                // Ignore these basic edit keys
                //-----------------------------

                case VK_RETURN:
                case VK_DELETE:
                case VK_BACK:
                case VK_ESCAPE:
                case VK_LEFT:
                case VK_RIGHT:
                case VK_UP:
                case VK_DOWN:
                case VK_SHIFT:
                case VK_CONTROL:
                ::TranslateMessage(pMsg);
                ::DispatchMessage(pMsg);
                break;

                //------------------
                // Process each CHAR
                //------------------
                
                default:
                c = pMsg->wParam;
                //----------------------------------------
                // This is my very simple per-character
                // validation routine. Invalid chars
                // are not passed on. Any validation 
                // code could be added here.
                //
                strEditIn = c;
                strEditIn.MakeUpper();
                strEditOut = ValidateText(strEditIn, 1,
                                                    FALSE);
                if (strEditIn != strEditOut)
                {
                    pMsg->wParam = 0;
                }
                //----------------------------------------
                ::TranslateMessage(pMsg);
                ::DispatchMessage(pMsg);
                break;
            }
            return (TRUE);
            break;
        }
    }
    return CDialog::PreTranslateMessage(pMsg);
}

However, bear in mind that some of the pre-defined virtual key codes can conflict with other character codes. For instance, VK_DOWN equals (0x28) (40), which is the same code as the open bracket '(' character. Normally, the down character isn't that important in single line Edit controls, but if you do need to include 'down' and the '(' character, you would have to use the WM_KEYDOWN message to record which key has actually been pressed.

For alphanumeric text, you could try the following:

BOOL CCMyDialog::PreTranslateMessage(MSG* pMsg)
{
    //----------------
    // Local variables
    //----------------

    CString strEditIn = "";
    CString strEditOut = "";
    TCHAR c;
    BOOL bPassThru = FALSE;

    //------------------------------
    // Get the window with the focus
    //------------------------------

    CWnd *pCont = GetFocus();

    //--------------------------------
    // Get list (or tree) edit control
    //--------------------------------
    
    CEdit *pEdit = m_ListCtrl.GetEditControl();
    //CEdit *pEdit = m_TreeCtrl.GetEditControl();

    //----------------------------------------------------
    // Only proceed if the edit control exists and has the
    // focus
    //----------------------------------------------------

    if (pCont == pEdit)
    {
        switch(pMsg->message)
        {
            //---------------------------
            // Catch the key down message
            //---------------------------

            case WM_KEYDOWN:

            //--------------------------------------------
            // Alphanumeric characters are between VK_HELP
            // and VK_LWIN
            //--------------------------------------------

            if ((pMsg->wParam <= VK_HELP) ||
                          (pMsg->wParam >= VK_LWIN))
            {
                bPassThru = TRUE;
            }

            //----------------------------
            // Catch the character message
            //----------------------------

            case WM_CHAR:
            switch(pMsg->wParam)
            {
                //--------------------------------
                // The backspace is a special case
                //--------------------------------

                case VK_BACK:
                ::TranslateMessage(pMsg);
                ::DispatchMessage(pMsg);
                break;

                //------------------
                // Process each CHAR
                //------------------
                
                default:
                if (!bPassThru)
                {
                    c = pMsg->wParam;
                    //-------------------------------------
                    // This is my very simple per-character
                    // validation routine. Invalid chars
                    // are not passed on. Any validation 
                    // code could be added here.
                    //
                    strEditIn = c;
                    strEditIn.MakeUpper();
                    strEditOut = ValidateText(strEditIn,
                                                 1, FALSE);
                    if (strEditIn != strEditOut)
                    {
                        pMsg->wParam = 0;
                    }
                    //-------------------------------------
                    ::TranslateMessage(pMsg);
                    ::DispatchMessage(pMsg);
                    return (TRUE);
                }
            }
            break;
        }
    }
    return CDialog::PreTranslateMessage(pMsg);
}