[Help]子线程中怎么想主窗体发消息

下面的代码想在线程中用PostMessage，向主窗体发消息，但是编译有错误。。。
////////////////////////////////////////////
//VoiceManager.cpp 线程所在的类
#define  WM_DISPLAY WM_USER+2 //接收消息

//线程功能函数
void CVoiceManager::ReceivingLoop(void)
{
while(bFlag)
{
//向主窗体发送消息
::PostMessage((HWND)(AfxGetApp()->m_pMainWnd),WM_DISPLAY,123,NULL);
}
} 
////////////////////////////////////////////
//voiceRecordDlg.h 主窗体对话框所在的类
#define  WM_DISPLAY WM_USER+2 //接收消息

//voiceRecordDlg.cpp
BEGIN_MESSAGE_MAP(CVoiceRecordDlg, CDialog)
//{{AFX_MSG_MAP(CVoiceRecordDlg)
ON_MESSAGE(WM_DISPLAY,OnDisplay)
//}}AFX_MSG_MAP
END_MESSAGE_MAP()

int k = 0;
LRESULT CVoiceRecordDlg::OnDisplay(WPARAM wParam,LPARAM lParam)
{
    CString tmp = (CString)wParam;
    m_List.InsertItem(k,tmp);
    k++;
    return 0;
}
////////////////////////////////////////////