Why "did" select and not "will"?


For the transition to the detailView, you implement “didSelectRowAtIndexPath”. Why not “will…”?
I´m asking because it didn´t work when I used the first one, and I don´t really know what to use the two different methods for. Wouldn´t one ("did"select) be enough?


Another example later in the chapter: “ViewWillAppear” is called instead of “ViewDidAppear”. In this case, I tried ViewWillAppear, and it is even smoother, because the details are already written down. If you call the “didAppear”, the detailView is visibly empty until it is fully on the screen and the details are loaded.
So another time: When can you use which method?