1-Basic concepts

What is the core animation, what to do with

Core animation is a composite engine whose job is to combine the different visual content on the screen as quickly as possible , and this content is
are decomposed into separate layers, stored in a system called a layer tree. So this tree forms the uikit as well as the iOS app when
The basics of everything you can see on the screen.

relationship of views to layers

The layer is really used to display and animate on the screen, and UIView is an encapsulation of it, providing some of the specific features of iOS that are similar to touch, as well as the advanced interface of the core animation underlying method.

Why does iOS offer two parallel hierarchies based on UIView and Calayer, and why not use a simple hierarchy to handle everything?

This is due to separation of duties, which avoids a lot of duplication of code. On iOS and Mac OS two platforms, there are many differences between event and user interaction, based on multi-touch user interface and mouse-based keyboard.

That's why iOS has Uikit and UIView, but Mac OS has AppKit and nsview reasons. They are functionally similar, but there are significant differences in implementation.

Drawing, layout, and animation, by contrast, are similar to the concept of iphone and ipad touch screens like Mac notebooks and desktop families. Separating the logic of this function and applying it to the independent core animation framework,

Apple is able to share code between iOS and Mac OS, making it easier for Apple's own OS development team and third-party developers to develop two-platform applications.

so calayer have what uiview do not have the function, need to go deep into the Calayer layer

Shadows, rounded corners, colored borders
3D transformations
Non-rectangular Range
Transparent matte
Multi-stage Nonlinear animation

1-Basic concepts