如何在“传统MFC代码”中的事件处理程序中添加回调？
这是使用MFC的旧代码实现的玩具。 OnBnClickedButton是一个事件处理程序，但它包含在其他线程中异步执行的代码（可能是一个坏主意）。声明语法被消息图接受。
//declaration
afx_msg void OnBnClickedButton();
//message map
ON_BN_CLICKED(IDC_BUTTON, &CMFCApplicationDlg::OnBnClickedButton)
现在，我想在事件处理程序中添加回调，但是消息映射不接受新的声明语法，该语法在哪里？
afx_msg void OnBnClickedButton(std::optional<std::function<CString(void)>> callback);
This is a toy implementation of a legacy code using MFC. OnBnClickedButton is an event handler but it contains codes which are executed asynchronously in a different thread ( may be a bad idea). The declaration syntax is accepted by the message map.
//declaration
afx_msg void OnBnClickedButton();
//message map
ON_BN_CLICKED(IDC_BUTTON, &CMFCApplicationDlg::OnBnClickedButton)
Now I want to add a callback to the event handler like so, but the message-map won't accept the new declaration syntax, where to go?
afx_msg void OnBnClickedButton(std::optional<std::function<CString(void)>> callback);
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MFC message Maps Maps中的函数签名和返回值是固定的。您必须遵循协议；它没有提供任何自定义点。如果
on_bn_clicked原型必须遵守以下签名，其不接受或返回任何值。唯一可用的状态是从消息映射条目中暗示的（即
onbnClickedButton，每当对话框的子控制器以cmfcapplicationdlg表示IDIDC_BUTTON 单击）。在实施
onbnClickedButton时，您可以随意执行任何您喜欢的事情，例如查询其他信息（例如，来自类实例或线程 - 本地存储中存储的数据），明确或旋转线程 MFC使用C ++ 20 Coroutines等。特别是，它没有为异步操作提供任何支持。这是您必须实施的事情。
The function signatures and return values for entries in MFC message maps are fixed. You have to follow the protocol; it doesn't offer any customization points. In case of the
ON_BN_CLICKEDbutton handler the prototype must abide to the following signatureIt doesn't accept or return any values. The only state available is that implied from the message map entry (i.e.
OnBnClickedButtonis called whenever the child control of the dialog represented byCMFCApplicationDlgwith IDIDC_BUTTONis clicked).In your implementation of
OnBnClickedButtonyou are free to do whatever you like, such as querying for additional information (e.g. from data stored in the class instance or thread-local storage), spinning up threads, either explicitly or using C++20 coroutines, etc.MFC doesn't help you with any of that, specifically it doesn't provide any sort of support for asynchronous operations. That's something you will have to implement yourself.