Stop program continuing WM_KEYDOWN process - winapi

Question

I'm not sure if it's the correct wording for my question but the issue revolves around it. I have 2 boxes that both validate on KillFocus. And another method which is called if the user presses the Next button, which calls a method that evaluates if they can continue, which validates these fields.
Due to how old this code base is, modifying this will cause issues elsewhere so I need to find a way around this without changing the way the can continue sequence is called. Here's some scenarios.
The user enters an invalid value in field 1, they press enter, the program fires the kill focus method and shows the error message, the enter key has pressed the next button which in turn validates the it again and shows the error again (different MsgBox same error). Meaning unless they unfocus manually then press enter they will always get two message boxes.
I believe this is due to the above reason as they have pressed enter which killed the focus instead of just calling can next.
Is there a way to stop the entire WM_KEYDOWN trail if it fails within the KillFocus method?
I'm sorry if this is a little bit vague and hazey, this is what I believe is happening.

Answer 1

#DavidHeffernan do you know of any other way to validate fields in the way that WM_KILLFOCUS does?
Allow me to make a suggestion. You can validate edit control's input in EN_CHANGE handler. From the docs:
Sent when the user has taken an action that may have altered text in an edit control.
Each time user types something, you will get this notification, which seems like a good place to validate data.
If data is invalid, you would then disable Next button using EnableWindow and indicate error somehow.
You could use EM_SHOWBALLOONTIP to pop tooltip with error message or simply change the background color of the edit control to red.
Below is the small example that illustrates my point. You should add better error checking of course, but the main idea is there:
#include <windows.h>
#include <CommCtrl.h>
#define IDC_BTN_NEXT 1000
#define IDC_BOX1 2000
#define IDC_BOX2 3000
// enable Visual Styles
#pragma comment( linker, "/manifestdependency:\"type='win32' \
name='Microsoft.Windows.Common-Controls' version='6.0.0.0' \
processorArchitecture='*' publicKeyToken='6595b64144ccf1df' \
language='*'\"")
// link with Common Controls library
#pragma comment( lib, "comctl32.lib")
void onBtnNext()
{
MessageBeep(0);
}
void onKillFocus(HWND box)
{
//==================== these are needed to disable Next button
HWND hwnd = ::GetParent(box);
if (NULL == hwnd) // critical error
return; // TODO: add error handling
HWND btnNext = ::GetDlgItem(hwnd, IDC_BTN_NEXT);
if (NULL == btnNext) // critical error
return; // TODO: add error handling
//==============================================================
int len = ::GetWindowTextLength(box);
if (0 == len) // it is ok, empty text, just return
return;
// if possible, use std::wstring here, I assumed you can't...
wchar_t *txt = new wchar_t[len +1];
if (0 == ::GetWindowText(box, txt, len + 1)) // critical error, according to documentation
{
// TODO: add error handling
delete[] txt;
return;
}
//====== simple validation for illustration only, treat uppercase letter as error
int isTextValid = ::isupper(txt[0]);
for (int i = 1; 0 == isTextValid && i < (len + 1); isTextValid = ::isupper(txt[++i]));
delete[] txt;
//==============================================
if (isTextValid)
{
EDITBALLOONTIP ebt;
ebt.cbStruct = sizeof(EDITBALLOONTIP);
ebt.pszText = L" Tooltip text";
ebt.pszTitle = L" Tooltip title";
ebt.ttiIcon = TTI_ERROR_LARGE;
if (!::SendMessage(box, EM_SHOWBALLOONTIP, 0, (LPARAM)&ebt))
{
//TODO: tooltip won't show, handle error
}
EnableWindow(btnNext, FALSE); // disable Next button
return; // our work is successfully done
}
if (!::SendMessage(box, EM_HIDEBALLOONTIP, 0, 0))
{
//TODO: tooltip won't hide, handle error
}
EnableWindow(btnNext, TRUE); // enable Next button
}
LRESULT CALLBACK WndProc(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam)
{
switch (msg)
{
case WM_CREATE:
{
HWND hwndBox1 = CreateWindowEx(0, WC_EDIT, L"",
WS_CHILD | WS_VISIBLE | WS_BORDER | ES_AUTOHSCROLL,
20, 20, 250, 20, hwnd, (HMENU)IDC_BOX1,
((LPCREATESTRUCT)lParam)->hInstance, 0);
if (NULL == hwndBox1) // add better error handling, this is for illustration only
return -1;
HWND hwndBox2 = CreateWindowEx(0, WC_EDIT, L"",
WS_CHILD | WS_VISIBLE | WS_BORDER | ES_AUTOHSCROLL,
20, 50, 250, 20, hwnd, (HMENU)IDC_BOX2,
((LPCREATESTRUCT)lParam)->hInstance, 0);
if (NULL == hwndBox2) // add better error handling, this is for illustration only
return -1;
HWND hwndBtnNext = CreateWindowEx(0, WC_BUTTON, L"Next",
WS_CHILD | WS_VISIBLE | BS_CENTER | BS_DEFPUSHBUTTON,
20, 80, 50, 25, hwnd, (HMENU)IDC_BTN_NEXT,
((LPCREATESTRUCT)lParam)->hInstance, 0);
if (NULL == hwndBtnNext) // add better error handling, this is for illustration only
return -1;
}
return 0L;
case WM_COMMAND:
{
switch (HIWORD(wParam))
{
case BN_CLICKED:
{
if (LOWORD(wParam) != IDC_BTN_NEXT)
break;
onBtnNext();
}
break;
case EN_CHANGE:
{
if (LOWORD(wParam) != IDC_BOX1 && (LOWORD(wParam) != IDC_BOX2))
break;
onKillFocus((HWND)lParam);
}
break;
default:
break;
}
}
break;
case WM_CLOSE:
::DestroyWindow(hwnd);
return 0L;
case WM_DESTROY:
{
::PostQuitMessage(0);
}
return 0L;
default:
return ::DefWindowProc(hwnd, msg, wParam, lParam);
}
return 0;
}
int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpCmdLine,
int nCmdShow)
{
WNDCLASSEX wc;
HWND hwnd;
MSG Msg;
wc.cbSize = sizeof(WNDCLASSEX);
wc.style = 0;
wc.lpfnWndProc = WndProc;
wc.cbClsExtra = 0;
wc.cbWndExtra = 0;
wc.hInstance = hInstance;
wc.hIcon = LoadIcon(hInstance, IDI_APPLICATION);
wc.hCursor = LoadCursor(NULL, IDC_ARROW);
wc.hbrBackground = GetSysColorBrush(COLOR_WINDOW);
wc.lpszMenuName = NULL;
wc.lpszClassName = L"Main_Window";
wc.hIconSm = LoadIcon(hInstance, IDI_APPLICATION);
if (!RegisterClassEx(&wc))
return 0;
INITCOMMONCONTROLSEX iccex;
iccex.dwSize = sizeof(INITCOMMONCONTROLSEX);
iccex.dwICC = ICC_STANDARD_CLASSES;
InitCommonControlsEx(&iccex);
hwnd = CreateWindowEx(0, L"Main_Window", L"Test",
WS_OVERLAPPED | WS_SYSMENU | WS_CAPTION,
50, 50, 305, 160, NULL, NULL, hInstance, 0);
ShowWindow(hwnd, nCmdShow);
UpdateWindow(hwnd);
while (GetMessage(&Msg, NULL, 0, 0) > 0)
{
TranslateMessage(&Msg);
DispatchMessage(&Msg);
}
return Msg.wParam;
}

Answer 2

The issue was solved in a "unconventional" way, but it worked. I noticed through debugging that the program lost focus twice on the box, once when ENTER was pressed and once when the message box popped up.
I used a static bool to avoid my program doing the error checking twice. It looks something like this -
void onKillFocus()
{
static bool isValidated = false;
if(!isValidated)
{
isValidated = true;
if(/*ValidationCheck*/)
{
//messagebox for error
}
}
}
By using this, the validation is only ran once when focus is killed stopping the message box from appearing twice, as the static bool is only alive for as long as the method is ran, meaning it's reset every time killfocus is called.