c++ - 一旦消息的当前实例在 MFC 中完成，如何发布消息？

Question

我对 Windows 应用程序中的消息没有足够的了解。

我有这个按钮处理程序:

void CChristianLifeMinistryEditorDlg::OnFilePublicTalk()
{
    CWeekendMeetingDlg dlgPublicTalk(this);

    if (m_pEntry != nullptr)
    {
        dlgPublicTalk.SetPublicTalkInfo(m_pEntry->GetPublicTalkInfo());
        dlgPublicTalk.SetCircuitVisitMode(m_iIncludeMode == kIncludeServiceTalk); // AJT v17.0.7
        // AJT v20.0.1
        dlgPublicTalk.SetSongInfo(
            CChristianLifeMinistryUtils::UseSingOutJoyfullyToJehovah(m_datFirstMonday), m_eForeignLang);
        auto iResult = dlgPublicTalk.DoModal();
        if (iResult == IDOK || iResult == to_underlying(CWeekendMeetingDlg::EndResult::PreviousDate) ||
                               iResult == to_underlying(CWeekendMeetingDlg::EndResult::NextDate))
        {
            m_pEntry->SetPublicTalkInfo(dlgPublicTalk.GetPublicTalkInfo());

            SetModified(true);
            UpdatePreview(m_iDateIndex);
            m_pHtmlPreview->Refresh2(REFRESH_COMPLETELY); // Ensure it has refreshed

            // Padlock
            // Reminder
            // Disable controls

            if (iResult == to_underlying(CWeekendMeetingDlg::EndResult::PreviousDate))
            {
                AfxMessageBox(_T("Move to previous week."));
                PostMessage(WM_COMMAND, ID_FILE_PUBLIC_TALK, 0);

                // It can't process this message until the current instance one has finished

            }
            else if (iResult == to_underlying(CWeekendMeetingDlg::EndResult::NextDate))
            {
                AfxMessageBox(_T("Move to next week."));
                PostMessage(WM_COMMAND, ID_FILE_PUBLIC_TALK, 0);

                // It can't process this message until the current instance one has finished
            }
        }
    }
}

我删除了代码(替换为两个 AfxMessageBox 调用)，但原则上我想重新启动相同的事件处理程序，就像用户在"file"菜单上单击它一样。可以用 PostMessage当消息的当前实例尚未终止时？

我还没有尝试过提供的答案，但是我在介绍两个 PostMessage时遇到了一个问题。调用:

void CChristianLifeMinistryEditorDlg::OnFilePublicTalk()
{
    CWeekendMeetingDlg dlgPublicTalk(this);

    if (m_pEntry != nullptr)
    {
        dlgPublicTalk.SetPublicTalkInfo(m_pEntry->GetPublicTalkInfo());
        dlgPublicTalk.SetCircuitVisitMode(m_iIncludeMode == kIncludeServiceTalk); // AJT v17.0.7
        // AJT v20.0.1
        dlgPublicTalk.SetSongInfo(
            CChristianLifeMinistryUtils::UseSingOutJoyfullyToJehovah(m_datFirstMonday), m_eForeignLang);

        // AJT v20.1.8
        dlgPublicTalk.SetPreviousNextDateButtonStates(m_btnMovePrevious.IsWindowEnabled(),
                                                      m_btnMoveNext.IsWindowEnabled());
        auto iResult = dlgPublicTalk.DoModal();
        if (iResult == IDOK || iResult == to_underlying(CWeekendMeetingDlg::EndResult::PreviousDate) ||
                               iResult == to_underlying(CWeekendMeetingDlg::EndResult::NextDate))
        {
            m_pEntry->SetPublicTalkInfo(dlgPublicTalk.GetPublicTalkInfo());

            SetModified(true);
            UpdatePreview(m_iDateIndex);
            m_pHtmlPreview->Refresh2(REFRESH_COMPLETELY); // Ensure it has refreshed

            if (iResult == to_underlying(CWeekendMeetingDlg::EndResult::PreviousDate))
            {
                PostMessage(WM_COMMAND, MAKEWPARAM(IDC_MFCBUTTON_PREVIOUS_DATE, BN_CLICKED),
                    (LPARAM)m_btnMovePrevious.GetSafeHwnd());
                PostMessage(WM_COMMAND, ID_FILE_PUBLIC_TALK, 0);
            }
            else if (iResult == to_underlying(CWeekendMeetingDlg::EndResult::NextDate))
            {
                PostMessage(WM_COMMAND, MAKEWPARAM(IDC_MFCBUTTON_NEXT_DATE, BN_CLICKED),
                    (LPARAM)m_btnMoveNext.GetSafeHwnd());
                PostMessage(WM_COMMAND, ID_FILE_PUBLIC_TALK, 0);
            }
        }
    }
}

执行操作并重新显示窗口后，然后单击取消我得到:



如果我更改它并直接调用按钮处理程序，如下所示:

void CChristianLifeMinistryEditorDlg::OnFilePublicTalk()
{
    CWeekendMeetingDlg dlgPublicTalk(this);

    if (m_pEntry != nullptr)
    {
        dlgPublicTalk.SetPublicTalkInfo(m_pEntry->GetPublicTalkInfo());
        dlgPublicTalk.SetCircuitVisitMode(m_iIncludeMode == kIncludeServiceTalk); // AJT v17.0.7
        // AJT v20.0.1
        dlgPublicTalk.SetSongInfo(
            CChristianLifeMinistryUtils::UseSingOutJoyfullyToJehovah(m_datFirstMonday), m_eForeignLang);

        // AJT v20.1.8
        dlgPublicTalk.SetPreviousNextDateButtonStates(m_btnMovePrevious.IsWindowEnabled(),
                                                      m_btnMoveNext.IsWindowEnabled());
        auto iResult = dlgPublicTalk.DoModal();
        if (iResult == IDOK || iResult == to_underlying(CWeekendMeetingDlg::EndResult::PreviousDate) ||
                               iResult == to_underlying(CWeekendMeetingDlg::EndResult::NextDate))
        {
            m_pEntry->SetPublicTalkInfo(dlgPublicTalk.GetPublicTalkInfo());

            SetModified(true);
            UpdatePreview(m_iDateIndex);
            m_pHtmlPreview->Refresh2(REFRESH_COMPLETELY); // Ensure it has refreshed

            if (iResult == to_underlying(CWeekendMeetingDlg::EndResult::PreviousDate))
            {
                //PostMessage(WM_COMMAND, MAKEWPARAM(IDC_MFCBUTTON_PREVIOUS_DATE, BN_CLICKED),
                //  (LPARAM)m_btnMovePrevious.GetSafeHwnd());
                OnBnClickedMfcbuttonPreviousDate();
                PostMessage(WM_COMMAND, ID_FILE_PUBLIC_TALK, 0);
            }
            else if (iResult == to_underlying(CWeekendMeetingDlg::EndResult::NextDate))
            {
                //PostMessage(WM_COMMAND, MAKEWPARAM(IDC_MFCBUTTON_NEXT_DATE, BN_CLICKED),
                //  (LPARAM)m_btnMoveNext.GetSafeHwnd());
                OnBnClickedMfcbuttonNextDate();
                PostMessage(WM_COMMAND, ID_FILE_PUBLIC_TALK, 0);
            }
        }
    }
}

后一种方法有效。我应该指出，这两个按钮处理程序更新一个 HTML 文件并在 Web 浏览器控件(实际上是在父对话框上)中重新绘制它。

像这样直接调用那些按钮处理程序是否可以接受？

使用提供的答案(谢谢)这运行良好:

void CChristianLifeMinistryEditorDlg::OnFilePublicTalk()
{
    delay_post_msg dpm{ this };
    CWeekendMeetingDlg dlgPublicTalk(this);

    if (m_pEntry != nullptr)
    {
        dlgPublicTalk.SetPublicTalkInfo(m_pEntry->GetPublicTalkInfo());
        dlgPublicTalk.SetCircuitVisitMode(m_iIncludeMode == kIncludeServiceTalk); // AJT v17.0.7
        // AJT v20.0.1
        dlgPublicTalk.SetSongInfo(
            CChristianLifeMinistryUtils::UseSingOutJoyfullyToJehovah(m_datFirstMonday), m_eForeignLang);

        // AJT v20.1.8
        dlgPublicTalk.SetPreviousNextDateButtonStates(m_btnMovePrevious.IsWindowEnabled(),
                                                      m_btnMoveNext.IsWindowEnabled());
        auto iResult = dlgPublicTalk.DoModal();
        if (iResult == IDOK || iResult == to_underlying(CWeekendMeetingDlg::EndResult::PreviousDate) ||
                               iResult == to_underlying(CWeekendMeetingDlg::EndResult::NextDate))
        {
            m_pEntry->SetPublicTalkInfo(dlgPublicTalk.GetPublicTalkInfo());

            SetModified(true);
            UpdatePreview(m_iDateIndex);
            m_pHtmlPreview->Refresh2(REFRESH_COMPLETELY); // Ensure it has refreshed

            if (iResult == to_underlying(CWeekendMeetingDlg::EndResult::PreviousDate))
            {
                //PostMessage(WM_COMMAND, MAKEWPARAM(IDC_MFCBUTTON_PREVIOUS_DATE, BN_CLICKED),
                //  (LPARAM)m_btnMovePrevious.GetSafeHwnd());
                OnBnClickedMfcbuttonPreviousDate();
                //PostMessage(WM_COMMAND, ID_FILE_PUBLIC_TALK, 0);
                dpm.set_active();
            }
            else if (iResult == to_underlying(CWeekendMeetingDlg::EndResult::NextDate))
            {
                //PostMessage(WM_COMMAND, MAKEWPARAM(IDC_MFCBUTTON_NEXT_DATE, BN_CLICKED),
                //  (LPARAM)m_btnMoveNext.GetSafeHwnd());
                OnBnClickedMfcbuttonNextDate();
                //PostMessage(WM_COMMAND, ID_FILE_PUBLIC_TALK, 0);
                dpm.set_active();
            }
        }
    }
}

我不得不使用两个 OnBnClickedMfcbuttonPreviousDate/ OnBnClickedMfcbuttonNextDate不使用 PostMessage 直接处理按钮处理程序模拟按钮点击。我认为这是可以接受的？

Answer 1

正如所写，这是安全的。 PostMessage生成 queued message在当前线程再次调用消息检索函数(如 GetMessage )之前，不会观察到这一点。然而，消息循环被阻塞，等待当前消息处理程序将控制权返回给它。

不幸的是，MFC 提供的(主)消息循环并不是可能调度消息的唯一代码。例如，对话框(如 MessageBox es)会启动它们自己的消息循环。菜单或窗口大小调整实现也是如此。有很多机会可以恢复到您试图防范的重入状态。

更强大的解决方案可以推迟 PostMessage在函数返回之前调用 to。 C++ 提供了实现这一点所需的所有工具:析构函数!

struct delay_post_msg {
    delay_post_msg(CWnd* w) : w_{ w }, active_{ false } {}
    void set_active() { active_ = true; }
    ~delay_post_msg()
    {
        if (active_) w_->PostMessage(WM_COMMAND, ID_FILE_PUBLIC_TALK, 0);
    }
private:
    CWnd* w_;
    bool active_;
};

你会像这样使用它:

void CChristianLifeMinistryEditorDlg::OnFilePublicTalk()
{
    // Objects are destroyed in the opposite order they are created.
    // If this object's d'tor needs to run last, it has to be created first.
    delay_post_msg dpm{ this };

    CWeekendMeetingDlg dlgPublicTalk(this);

    // ...

    if (some_condition)
    {
        dpm.set_active();
    }

    // ...

    // If active, the d'tor of dpm posts the message just before leaving this function.
}