iOS Framework Overview

iOS is an operating system running on iphone, IPod touch or ipad, previously called iphone Os,ios and Mac OS X have a common infrastructure and underlying technology. iOS is designed for mobile devices, so it's slightly different from Mac OS X systems, such as support for multi-touch and acceleration sensors.

Let's look at an introduction to the iOS framework:
The system architecture of IOS is divided into four tiers: the core OS layer, the core service layer, the media layer, and the Cocoa touch layer. Shows a comparison of the architecture levels of Mac OS X and iOS.

We can see that Mac OS X and iOS have a different system architecture hierarchy than the top tier, replaced by the Cocoa Framework for Cocoa Touch, so developing an iOS app is similar to developing a Mac OS X program, so let's take a look at what each layer contains.
In fact, iOS is UNIX-based, so we can trust this operating system, you know, from the stability of the system to say that it is much better than other operating system products.
The bottom layer of the iOS system architecture is the core operating system layer, which includes memory management, file systems, power management, and some other operating system tasks. It can interact directly with the hardware device. The core operating system layer includes the following components:
os X Kernelmach 3.0bsd
socketspower Mgmtfile System
keychaincertificatessecurity
bonjour
The second tier is the core service layer, which we can use to access some of the iOS services. It includes the following components:
collectionsaddress booknetworking
file Accesssqlitecore Location
net servicesthreadingpreferences
url Utilities
The third layer is the media layer, through which we can use a variety of media files in the application, for audio and video recording, graphic drawing, as well as the production of basic animation effect. It includes the following components:
core Audioopenglaudio Mixing
audio Recordingvideo Playbackjpg,png,tiff
pdfquartzcore Animation
opengl ES
The topmost layer is the touch layer, which provides a variety of useful frameworks for our application development, and most of it relates to the user interface, which is essentially responsible for the user's touch interaction on the iOS device. It includes the following components:
multi-touch Eventscore Motioncamera
view Hierarchylocalizationalerts
web viewsimage Pickermulti-touch Controls
Many of the technologies in the cocoa touch layer are based on the Objective-c language. The Objective-c language provides support for iOS like collections, file management, network operations, and more. Like the Uikit framework, it provides a variety of visual components for applications such as window, view, and button components (UIButton). Other frameworks in the Cocoa touch layer are also useful for our development in the application, such as access to the user's correspondence function framework, the framework for obtaining photo information, and the hardware support for the accelerometer and the three-dimensional gyroscope.

iOS Framework Introduction

What is a framework? It is essentially a software library that helps us accomplish a variety of specific functions.
The application projects we wrote started with the cocoa touch layer, specifically from the Uikit framework. When there are some special functions that need to be used in the process of writing a program, we should start by looking for the appropriate framework from the top of the framework, and use the underlying technology only if the superstructure is not able to solve it. In fact, the top-level framework already covers most of the features we need.
Table 1-1 lists some of the commonly used iOS SDK frameworks.