This diagram illustrates the roadmap for becoming an iOS developer. I updated it to reflect recent changes in 2021. I have tried to collect the most important technical skills that a progressing iOS developer can learn, in a logical order, to succeed more and more.
Without any doubt, Swift is the main programming language for developing new applications for Apple developers, but there are many apps on the App store that have been developed using Objective-C. Many of these apps are serving millions of users worldwide. So to build your career, you probably need to be able to read or even write Objective-C codes.
Based on the memory handling methods, types in Swift are divided into two different categories: value types and reference types. There are some basic differences between value and reference types which causes them to behave differently in the same conditions. So developers should know their specifications to write logical codes both during working with Apple’s predefined types and during defining their own custom types.