Bind Dialog Procedure as method to custom class [duplicate] - c++

Question

This question already has answers here:
Use class member as WNDPROC/DLGPROC with or without global
(3 answers)
Closed 7 years ago.
I am trying to work my way around the WINAPI to implement the procedure of a modeless Dialog window as member of a custom class. I am not sure it is possible, but I hoped someone knew a way. The goal is to have a procedure with access to member variables of the custom Class
I know it is possible using normal windows.
Example:
//MyClass.h
class MyClass
{
public:
bool init( ... )
static LRESULT CALLBACK redirect(HWND hWnd, UINT msg,
LPARAM lParam, WPARAM wParam);
LRESULT myWndProc(HWND hWnd, UINT msg,
LPARAM lParam, WPARAM wParam);
private:
HWND m_MainHwnd;
}
By defining a static member function that redirects the pointer to the nonstatic actual procedure handling, the procedure can be a member function:
//MyClass.cpp
MyClass::init( ... )
{
//Create the window class for the main Window//
m_windowed = windowed;
WNDCLASSEX wc; //Create a new extended windows class
wc.cbSize = sizeof(WNDCLASSEX); //Size of our windows class
wc.style = CS_HREDRAW | CS_VREDRAW; //class styles
wc.lpfnWndProc = MyClass::redirect; //Default windows procedure function
wc.cbClsExtra = NULL; //Extra bytes after our wc structure
wc.cbWndExtra = NULL; //Extra bytes after our windows instance
wc.hInstance = hInstance; //Instance to current application
wc.hIcon = LoadIcon(NULL, IDI_WINLOGO); //Title bar Icon
wc.hCursor = LoadCursor(NULL, IDC_ARROW); //Default mouse Icon
wc.hbrBackground = CreateSolidBrush(0xFFFFFF); //Window bg color
wc.lpszMenuName = NULL; //Name of the menu attached to our window
wc.lpszClassName = m_windowName; //Name of our windows class
wc.hIconSm = LoadIcon(NULL, IDI_WINLOGO); //Icon in your taskbar
if (!RegisterClassEx(&wc)) //Register our windows class
{
//if registration failed, display error
MessageBox(NULL, "Error registering Main Window class",
"Error", MB_OK | MB_ICONERROR);
return false;
}
m_MainHwnd = CreateWindowEx( //Create our Extended Window
NULL, //Extended style
m_windowName, //Name of our windows class
m_windowName, //Name in the title bar of our window
WS_OVERLAPPEDWINDOW | WS_VISIBLE, //style of our window | Make it visible on showWindow cmd
30, 30, //Top left corner of window
width, //Width of our window
height, //Height of our window
NULL, //Handle to parent window
NULL, //Handle to a Menu
hInstance, //Specifies instance of current program
this //used for an MDI client window
);
}
See the line in the setup in WNDCLASSEX: wc.lpfnWndProc = MyClass::redirect;? This is valid because the the following implementation of the redirect static function:
MyClass::redirect(HWND hwnd, UINT msg, LPARAM lParam, WPARAM wParam)
{
if (msg == WM_CREATE) SetWindowLongPtr(hwnd, GWL_USERDATA, (LONG_PTR)((CREATESTRUCT FAR *)lParam)->lpCreateParams);
MyClass * pObject = (MyClass*)((LONG_PTR)GetWindowLongPtr(hwnd, GWL_USERDATA));
if (pObject) return pObject->MyWndProc(hwnd, msg, wParam, lParam);
//return the message for windows to handle it
return DefWindowProc(hwnd,
msg,
wParam,
lParam);
};
This lets you implement the MyWndProc ( ... ) exactly like any other member method.
Now! I really want to be able to do the same thing to my Modeless Dialog box - because it's rather important that it knows the member variables of "MyClass". Also - I like that I can design it and redesign it as I like ( If I have to use normal windows - It'd be tedious to design it all in code. )
Is it possible?
Thank you in advance!

Answer 1

Yes it's possible to use this method with a dialog box, in more or less the same way.
Instead of using WM_CREATE to store the this pointer you use WM_INITDIALOG. Note that the user data is passed to WM_INITDIALOG in lParam itself - there are no structures to dereference like there is with WM_CREATE.
You can store the pointer in DWLP_USER which is a pointer-size window data slot available to the owner of the dialog box.
The final difference is simply return FALSE if the data pointer hasn't been assigned yet - you don't call DefWindowProc from a dialog procedure.
class MyClass
{
public:
static INT_PTR CALLBACK dlgRedirect(HWND hWnd, UINT uMsg, WPARAM wParam, LPARAM lParam);
LRESULT myDlgProc(HWND hWnd, UINT uMsg, WPARAM wParam, LPARAM lParam);
}
//...
HWND hwndDlg = DialogBoxParam(hInstance, MAKEINTRESOURCE(IDD_MYDIALOG), hwndParent,
MyClass::dlgRedirect, reinterpret_cast<LPARAM>(this));
//...
INT_PTR CALLBACK MyClass::dlgRedirect(HWND hWnd, UINT uMsg, WPARAM wParam, LPARAM lParam)
{
if (uMsg == WM_INITDIALOG) SetWindowLongPtr(hWnd, DWLP_USER, lParam);
MyClass* pThis = reinterpret_class<MyClass*>(GetWindowLongPtr(hWnd, DWLP_USER));
if (pThis) return pThis->myDlgProc(hWnd, uMsg, wParam, lParam);
return FALSE;
}
INT_PTR MyClass::myDlgProc(HWND hWnd, UINT uMsg, WPARAM wParam, LPARAM lParam)
{
// real dialog procedure here
}