How to cancel item label editing in Tree-View control upon ESC keydown in WinAPI

Question

I have a dialog box with a Tree-View control where the user can edit the item labels. I want the user to be able to cancel the label edit by pressing ESC key.

The problem is that pressing ESC closes the dialog window immediately.

I have tried getting the handle to the EditBox control by a TreeView_GetEditControl() call upon TVN_BEGINLABELEDIT message and subclassing it to trap the ESC key, but when I do that, typing in edit box becomes impossible.

What is the problem?

Here is the relevant code:

INT_PTR CALLBACK DlgProc(HWND hWnd, UINT message, 
                         WPARAM wParam, LPARAM lParam) {
    switch(message) {
        //...

        case WM_NOTIFY:
        {
            LPNMHDR pNmHdr = (LPNMHDR)lParam;
            switch(pNmHdr->code) {
                case TVN_BEGINLABELEDIT:
                {
                    HWND hwndTV = (HWND)GetWindowLongPtr(hWnd, GWLP_USERDATA); // stored handle to Tree-View ctl
                    HWND hWndEditBox = TreeView_GetEditControl(hwndTV);

                    // subclass edit box
                    TreeViewGlobals::g_wpOrigEditBoxProc =
                        (WNDPROC)SetWindowLongPtr(hWndEditBox, 
                                                  GWLP_WNDPROC, (LONG_PTR)EditBoxCtl_SubclassProc);
                    break;
                }
                case TVN_ENDLABELEDIT:
                {
                    SetWindowLongPtr(hWnd, DWLP_MSGRESULT, (LONG)TRUE); // accept edit
                    return TRUE;
                }
                default:
                    break;
            }
        }
        default:
            break;
    }

    return FALSE;
}

INT_PTR CALLBACK EditBoxCtl_SubclassProc(HWND hWndEditBox, UINT message,
                                         WPARAM wParam, LPARAM lParam) {
    switch(message) {
        HANDLE_MSG(hWndEditBox, WM_GETDLGCODE, EditBoxCtl_OnGetDlgCode);
        HANDLE_MSG(hWndEditBox, WM_KEYDOWN, EditBoxCtl_OnKey); // does not receive WM_KEYDOWN for ESC unless I handle WM_GETDLGCODE above
        default:
            break;
    }

    return CallWindowProc(TreeViewGlobals::g_wpOrigEditBoxProc, 
                          hWndEditBox, message, wParam, lParam);
}

UINT EditBoxCtl_OnGetDlgCode(HWND hWndEditBox, LPMSG lpmsg) {
    if(lpmsg) {
        if(lpmsg->message == WM_KEYDOWN && lpmsg->wParam == VK_ESCAPE) {
            return DLGC_WANTMESSAGE;
        }
    }

    return 0;
}

void EditBoxCtl_OnKey(HWND hWndEditBox, UINT vk, BOOL fDown, 
                      int cRepeat, UINT flags) {
    switch(vk) {
        case VK_ESCAPE:
                Beep(4000, 150); // never beeps
            break;
        default:
            break;
    }
}

---

P.S. I noticed that when I remove WM_GETDLGCODE handler in EditBoxCtl_SubclassProc(), it becomes possible to type in the edit box again, but then I can't trap WM_KEYDOWN for ESC key from that procedure.

Answer 1

Below is the solution that I found. The trick seems to be calling the original control proc with WM_GETDLGCODE intercepted in subclass proc, storing the return value and then returning it with DLGC_WANTALLKEYS or DLGC_WANTMESSAGE flag set to prevent system from further processing the keystroke.

The upside to this approach is that pressing ESC cancels editing and reverts the item label to its original text, and pressing ENTER while editing no longer just closes the dialog(which was another problem) without any additional code to handle those cases.

Here is the code that works:

INT_PTR CALLBACK EditBoxCtl_SubclassProc(HWND hWndEditBox, UINT message,
                                         WPARAM wParam, LPARAM lParam) {
    switch(message) {
        //HANDLE_MSG(hWndEditBox, WM_GETDLGCODE, EditBoxCtl_OnGetDlgCode);  // can't use this: need wParam and lParam for CallWindowProc()

        case WM_GETDLGCODE: {   
            INT_PTR ret = CallWindowProc(TreeViewGlobals::g_wpOrigEditBoxProc, 
                                         hWndEditBox, message, wParam, lParam);
            MSG* lpmsg = (MSG*)lParam;  
            if(lpmsg) {
                if(lpmsg->message == WM_KEYDOWN && 
                  (lpmsg->wParam == VK_ESCAPE || lpmsg->wParam == VK_RETURN) ) 
                {
                    return ret | DLGC_WANTALLKEYS;
                }
            }

            return ret;
        }

        default:
            break;
    }

    return CallWindowProc(TreeViewGlobals::g_wpOrigEditBoxProc, 
                          hWndEditBox, message, wParam, lParam);
}