Protocols

Handle touch event for button in DownloadTrackerCell. DownloadListController conforms to the protocol. If you want DownloadListController to handle touch event for your custom UITableViewCell, implement assignAccessoryButtonDeletegate(_:) in protocol DownloadActivityTrackable and in button’s action method, send the only protocol method to delegate object.

Make UITableViewCell coordinate with DownloadListController to:

1. track download activity;
2. handle button touch event;
3. update button’s title or image.

All properties and methods in the protocol are optional. I have made UITableViewCell conform to this protocol in extension and don’t implement any property or method.