Dialog callback function doesn't get called - c++

Question

I'm struggling properly creating a dialog box.
The first problem was getting the dialog box itself visible. When displaying a dialog it did only show controls inside of the dialob box, but the dialog box itself were invisiblem but it was still possible to press the close button. I fixed this by adding a custom class name to the dialog boxes properties and registering the class. Does someone know what exactly the problem was? A colleague of mine didn't need to explicit register the class and add it to the dialog boxes properties.
But my current problem is as follows:
I have this callback function:
static BOOL CALLBACK DialogProc(HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam)
{
switch(message)
{
case WM_INITDIALOG:
MessageBox(NULL, L"init dialog", L"Message Box", NULL);
break;
case WM_CLOSE:
DestroyWindow(hwnd);
MessageBox(NULL, L"close dialog", L"Message Box", NULL);
break;
case WM_DESTROY:
MessageBox(NULL, L"destroying dialog", L"Message Box", NULL);
break;
}
return TRUE;
}
and this initiation of a new dialog box:
BOOL InitInstance(HINSTANCE hInstance, int nCmdShow)
{
HWND hWnd;
TCHAR szTitle[MAX_LOADSTRING] = TEXT("This is the DialogBox Title"); // Titelleistentext
TCHAR szWindowClass[MAX_LOADSTRING] = TEXT("MyDialogBoxClass"); // Klassenname des Hauptfensters
g_hInst = hInstance; // Instanzenhandle in der globalen Variablen speichern
if (!MyRegisterClass(hInstance, szWindowClass))
{
return FALSE;
}
hWnd = CreateDialog(hInstance, MAKEINTRESOURCE(IDD_DIALOG_FTPHELPER), NULL, DialogProc);
if (!hWnd)
{
return FALSE;
}
SetWindowText(hWnd, szTitle);
ShowWindow(hWnd, nCmdShow);
UpdateWindow(hWnd);
if (g_hWndCommandBar)
{
CommandBar_Show(g_hWndCommandBar, TRUE);
}
return TRUE;
}
When displaying a new dialog box it doesn't call the "DialogProc" function not even once, never, it makes me sick...
Does someone know the answer to this problem?
best greetings and thank you for your help!

Answer 1

Your DialogProc function always returns TRUE, meaning that it handled whatever message it received. However, you only actually handle three messages, and there are many others (such as WM_CREATE) that are called by the system in order to 'set up' the dialog window.
You should only return TRUE if you have completely handled the message, and FALSE otherwise, so that the system can call the default procedure for messages that you don't handle.
From the Microsoft documentation:
Typically, the dialog box procedure should return TRUE if it processed
the message, and FALSE if it did not. If the dialog box procedure
returns FALSE, the dialog manager performs the default dialog
operation in response to the message.