Here are some links that made me understand key topics to develop apps in iOS, also, some of this links solve problems or questions I had while coding.
- Method dispatch in Swift (RightPoint - Brian King)
 - What is key-value Observing (Hacking with swift)
 - Swift Documentation (NShipter - Nate Cook)
 - Create iOS reminders programatically (Flip Nemeck)
 - UISearchController and UISearchBar (Kodeco)
 - If let case (short syntax to unwrap result values)
 
- SOLID Principles (Kodeco)
 - Protocol composition (Marco Santa Dev)
 - SOLID Principles Applied to Swift (Marco Santa Dev)
 - Dependency injection in Swift (CocoaCast)
 - Dependency injection in Swift with Protocols (Swift with Majid)
 - Some keyworkd in swift
 - How to use any and some
 - Difference between any and some
 
- Constructing Urls in Swift (Swift by Sundel)
 - Writing Network Library with Combine ando Codable (Danel Bernal)
 - Minimal network layer from scratch (Medium - Fernando Martin Ortiz)
 - Protocol base generic Network using JSONDecoder (James Rochabrum)
 
- What does 
nonisolatedmean? - What does 
dynamicdoes in swift?