【iOS Design Pattern】The most important design patterns you must know

Model-View-Controller—This design pattern governs the overall structure of your app.

Delegation—This design pattern facilitates the transfer information and data from one object to another.

Target-action—This design pattern translates user interactions with buttons and controls into code thatyour app can execute.

Block objects—You use blocks to implement callbacks and asynchronous code.

Sandboxing—All iOS apps are placed in sandboxes to protect the system and other apps. The structure of the sandbox affects the placement of your app’s files
and has implications for data backups and some app-related features. 

Reference: iOS App Programming Guide