[Swift] An illustration for those who say "Delegate is an agent."

Introduction

Anyone who started Swift would have thought first Teaching materials / articles "Delegate is an agent .." Reader "What is an agent?"

In this article, I will introduce Delegate graphically and explain how to use it. By the time you finish reading "I see, Delegate is an agent." You're probably thinking.

Understand Delegate

Below, the protocol PopViewDelegate: UIView part is incorrect class PopupView: It will be UIView.

At the end

What did you think? I think you thought, "Delegate is an agent." If anyone around you is having trouble understanding Delegate, please do Please introduce this article.