为什么最小的MFC项目在Visual Studio 2013上有链接错误？

Question

I created a Win32 console application to write a simples MFC project.

The source code is as follow:

#include <afxwin.h>

class MyApp : public CWinApp
{
public:
    BOOL InitInstance();

    MyApp()
    {
    }
};

class MainWindow : public CFrameWnd
{
protected:
    int OnCreate(LPCREATESTRUCT lpCreateStruct);
    void OnClose();
    LRESULT OnTimer(WPARAM wParam, LPARAM lParam);

    // This line is causing the error
    DECLARE_MESSAGE_MAP()
};

BOOL MyApp::InitInstance()
{
    MainWindow* mainWindow = new MainWindow();

    m_pMainWnd = mainWindow;
    mainWindow->Create(NULL, L"Main Window");
    mainWindow->ShowWindow(m_nCmdShow);

    return TRUE;
}

MyApp myApp;

int MainWindow::OnCreate(LPCREATESTRUCT lpCreateStruct)
{
    SetTimer(1, 2000, NULL);
    return 0;
}

void MainWindow::OnClose()
{
    if (MessageBox(L"Close?", L"Close", MB_YESNO | MB_ICONQUESTION) == IDYES)
    {
        KillTimer(1);
        CFrameWnd::OnClose();
    }
}

LRESULT MainWindow::OnTimer(WPARAM wParam, LPARAM lParam)
{
    MessageBeep(MB_ICONQUESTION);
    return 0;
}

When I try to compile I get the following error:

Error 1 error LNK2001: unresolved external symbol "protected: virtual struct AFX_MSGMAP const * __thiscall MainWindow::GetMessageMap(void)const " (?GetMessageMap@MainWindow@@MBEPBUAFX_MSGMAP@@XZ) D:\\Projects\\MinimumMFC\\MinimumMFC\\MinimumMFC.obj MinimumMFC

Answer 1

I forgot to declare the BEGIN_MESSAGE_MAP after the MainWindow declaration:

BEGIN_MESSAGE_MAP(MainWindow, CFrameWnd)
    ON_WM_CREATE()
    ON_WM_CLOSE()
    ON_MESSAGE(WM_TIMER, OnTimer)
END_MESSAGE_MAP()

The full source code should be:

#include <afxwin.h>

class MyApp : public CWinApp
{
public:
    BOOL InitInstance();

    MyApp()
    {
    }
};

class MainWindow : public CFrameWnd
{
protected:
    afx_msg int OnCreate(LPCREATESTRUCT lpCreateStruct);
    afx_msg void OnClose();
    afx_msg LRESULT OnTimer(WPARAM wParam, LPARAM lParam);

    DECLARE_MESSAGE_MAP()
};

BEGIN_MESSAGE_MAP(MainWindow, CFrameWnd)
    ON_WM_CREATE()
    ON_WM_CLOSE()
    ON_MESSAGE(WM_TIMER, OnTimer)
END_MESSAGE_MAP()

BOOL MyApp::InitInstance()
{
    MainWindow* mainWindow = new MainWindow();

    m_pMainWnd = mainWindow;
    mainWindow->Create(NULL, L"Main Window");
    mainWindow->ShowWindow(m_nCmdShow);

    return TRUE;
}

MyApp myApp;

int MainWindow::OnCreate(LPCREATESTRUCT lpCreateStruct)
{
    SetTimer(1, 2000, NULL);
    return 0;
}

void MainWindow::OnClose()
{
    if (MessageBox(L"Close?", L"Close", MB_YESNO | MB_ICONQUESTION) == IDYES)
    {
        KillTimer(1);
        CFrameWnd::OnClose();
    }
}

LRESULT MainWindow::OnTimer(WPARAM wParam, LPARAM lParam)
{
    MessageBeep(MB_ICONQUESTION);
    return 0;
}