MFC - Cannot Post Message to a custom class derive

问题:

I have a custom class derived from CWnd that I would like to post a message to from a worker thread. I am using the PostMessage function to achieve this. The first argument to PostMessage is the HWND type handle to my class, and the next is the message I would like handled. For the first parameter, I generate the handle to my class using GetSafeHwnd() function, and for the second parameter, I use WM_USER+3. Also, I declare a message map inside my class header file, and add an entry for the message handler inside the BEGIN_MESSAGE_MAP and END_MESSAGE_MAP block. However, my handler is not getting called. I have also checked the return value of PostMessage function, it is 1, that means success.

Here is my code :

Inside MyClass.h

class CMyClass : CWnd
{
....
.... 
public:
void InitHandle();

protected:
afx_msg LRESULT OnMessageReceived(WPARAM wParam, LPARAM lParam);
DECLARE_MESSAGE_MAP()
} 

Inside MyClass.cpp

#define WM_MY_MESSAGE WM_USER+3

HWND handleToMyClassWindow;

BEGIN_MESSAGE_MAP(CMyClass, CWnd)
    ON_MESSAGE(WM_MY_MESSAGE, OnMessageReceived)
END_MESSAGE_MAP()

LRESULT CMyClass::OnMessageReceived(WPARAM wParam, LPARAM lParam)
{ .... }

void CMyClass::InitHandle()
{ 
    handleToMyClassWindow = GetSafeHwnd();
}

Inside Worker thread

UINT WorkerThreadFunction(LPVOID pParam )
{ 
....
PostMessage(handleToMyClassWindow, WM_MY_MESSAGE, NULL, NULL);
....
}

My question is, what are the possible reasons for the OnMessageReceived handler to not be called.

P.S.

I take care that the calling object calls the InitHandle() function.

I tried the same technique with the View class (derived from CView) of my program, and it works there, but fails here.

回答1:

You cannot post to a window if it has not been created. GetSafeHwnd() will return NULL if you have not actually created a window using your class.