A while ago I got a question if 3-level expandable list views can be implemented in Android. Android does not explicitly support it but the flexibility of Android UI widget framework provides a relatively simple implementation option: second-level expandable list views are to be inserted into the first-level expandable list view as child views. There was a blog post with an example program and everybody was happy. Even then I made a note that I don't agree with the approach from the UI point of view because the display becomes unnecessarily messy.
Now there was a comment at that blog post whether 4-level lists are
possible. Of course they are possible, it is just not a good UI design.
But I guess, you better try it yourself if you don't believe me. The
principle is the same (expandable lists embedded as children of
higher-level expandable lists), it is just much more complex to make
sure that everything is recalculated correctly for every event. In
order to follow the operation, I left a good amount of debugging code
in the project.
Click here to access the example program.