I have previously asked about the proper way of accessing member variables present in the project. In the project, I have CWinapp-derived class, CMainFrm class, a list of different view classes. However, currently, I have instances of different user-defined classes instantiated in the CWinApp-derived class, while the rest of the classes use a pointer obtained from AfxGetApp() function, and then access the different user-defined classes. I was told by some community members on the MFC newsgroup that this is a very bad design (i.e. the parent should not know anything about an app-class, view class, or document class). However, I'm not sure how otherwise I can access various user-defined classes without using this design. It would be great to hear some suggestions as I'm not familiar enough with MFC to come up with proper search terms.
"(i.e. the parent should not know anything about an app-class, view class, or document class)"
I'm not sure I understand this sentence, what do you mean with 'parent' here?
Anyway, in my opinion, the design you describe isn't really a problem. It's a trade off: do you either pass these classes to all functions that need them, complicating their use and API, or do you store them as a sort of global variables like you're doing? It depends on the data that is accessed, and how often. Data that is needed in many places can just as well be 'global'.
There are multiple ways of making data 'global': make it a member of CWinApp (that is, your CWinApp-derived class), or of CMainFrame, or do you make an actual 'global variable', or do you make a singleton, ...
The problem with global variables is that it becomes hard to figure out who accesses it when and from where. If you data as a member of CWinApp, you can access it through an accessor function and trace access from there (through log messages, break point, ...) This, in my opinion, mitigates most of the problems associated with global variables. What I usually do nowadays is use a Loki singleton.
The reason that is stated in your post for not making data a member of CWinApp, as a decoupling issue, is (in the context that you've presented it) a bit strange imo. If certain classes need access, they'll need to know of those data structures anyway, and their storage location is irrelevant. Maybe it's just because I don't know about the specifics of your design.