In iOS, a popup is shown from time to time that asks the user to join a Wi-Fi network.

I want to implement a similar popup with custom contents
- Title
- TableView with a varying amount of entries (if too many, with scrollbar)
- Cancel button
-
Popup over an existing view (the popup is smaller than the view)
-
How can such an effect be achieved? I guess that UIAlertView may be a good starting point. However, UIAlertView does not support subclassing
The UIAlertView class is intended to be used as-is and does not support subclassing. The view hierarchy for this class is private and must not be modified.
Not with the system UIAlertView. You have to code your own, or use an open source component.
This could be a starting point/example: BlockAlertsAnd-ActionSheets