IOS overview-see the documentation before development

IOSIs running onIPhoneThe operating system of iPod touch and iPad devices. It manages device hardware and provides basic technology for the implementation of local mobile apps. Different operating systems have different system applications, such as Phone, Mail, and Safari, which can provide users with standard system services.

The iPhone SDK contains the tools and interfaces required to develop, install, and run local applications. Use local applicationsIOSThe system framework and Objective-C language are constructed and run directly onIOSDevice. It is different from a web application. One is that it is located on the installed device, and the other is that it can run regardless of whether there is a network connection. Local applications have the same status as other system applications. Both local applications and user data can be synchronized to the user's computer through iTunes.

IOS Architecture

The architecture of iOS is similar to that of Mac OS. At the advanced level, iOS acts as an intermediary between underlying hardware and applications that are displayed on the screen), as shown in Figure 1-1. The application you created cannot directly access the hardware, but must interact with the system interface. In turn, the system interface deals with appropriate drivers. This abstraction prevents your applications from changing the underlying hardware.

Figure 1-1 The application is on the upper layer of iOS

Note: Although applications are usually isolated from the underlying hardware, application code still needs to consider some differences between devices. For example, iPad and iPod touch cannot open a URL containing a phone number, But iPhone can.

The iOS implementation can be seen as a collection of multiple layers. The "Game Kit framework" contains an introduction to these layers. The underlying layer provides basic services for all applications, senior management includes some complicated and clever services and technologies.

Figure 1-2 iOS Layer

When writing code, you should try to use the high-level framework instead of the underlying framework. The high-level framework provides object-oriented abstraction for underlying structures. These abstractions can reduce the number of lines of code to be written, and encapsulate complex functions such as socket and thread to make code writing easier. Although the high-level framework abstracts the underlying structure, it does not block the underlying technology. If the high-level framework does not provide interfaces for some functions of the underlying framework, developers can directly use the underlying framework.

Subsequent sections of this document describe the technologies and frameworks contained in each layer.

What does the iPhone SDK contain?

All interfaces, tools, and resources required for developing iOS applications on Intel-chip Macintosh computers are included in the iPhone SDK.

Apple released most of the system interfaces to the special data packets such as the framework. A framework is a directory that contains a dynamic shared library and resources required to use the library, such as header files, images, and help applications ). To use a framework, you need to link it to the application project, similar to using other shared libraries. In addition, you need to tell the development tool where to find the framework header file and other resources.

In addition to the framework, Apple also publishes some technologies in the form of a standard shared library. Because iOS is UNIX-based, many underlying technologies of the operating system are sourced from open-source technologies, and many interfaces of these technologies can be accessed from the standard library and Interface directory.

The SDK also contains the following important components:

Xcode tool-Provides iOS application development tools, including the following key applications:

Xcode is an integrated development environment that manages application projects. You can use it to edit, compile, run, and debug code. Xcode also integrates many other tools, which are the main applications used during development.

Interface Builder-a tool that assembles user interfaces visually. The Interface objects created through Interface Builder will be saved to resource files in a specific format and loaded to the application at runtime.

Instruments-runtime Performance Analysis and debugging tools. You can use Instruments to collect the behavior information when the application is running and use the information to identify possible problems.

IPhone Simulator-a Mac OS X platform application that simulates the iOS technology stack so that you can test iOS applications on Intel-based Macintosh computers.

IOS Reference Library-the SDK contains iOS reference documents by default. In addition, if the document library is updated, the update will be automatically downloaded to the local device. Select Help> Developer Documentation to view the reference library.

The SDK provides the software required to write applications, and Xcode and Instruments allow you to directly interact with the bound device, run and debug the code on the target hardware. If you need to develop on the actual device, please join the paid iPhone developer program of Apple and configure the device for development purpose. For more information about the iPhone developer program, visit http://developer.apple.com/iphone/program.

If you need to know how to install the iPhone SDK and how to use the iPhone SDK to develop iOS applications, refer to the iOS development guide. If you want to learn more about the iOS framework and find the underlying system library, see "iOS framework ".

What applications can you create on iOS?

You can run two different types of custom applications on the device: Web applications and local applications. Web applications combine HTML, stacked style sheets, and JavaScript code to implement interactive applications. These applications exist on web servers, it is transmitted to the user's device over the network and runs on the Safari browser. Local applications are directly installed on the device and run without network connection.

The iPhone SDK can only be used to create local applications that are displayed on the Home screen of a device. It does not support creating other types of code, such as drivers, frameworks, and dynamic libraries. If you want to integrate a framework or dynamic library into an application, you should statically link it to the application execution file during the blockchain project.

How to Use the Reference Library?

The iOS Reference Library contains various documents, sample code, and tutorials, which can help you write applications. However, the reference library contains thousands of pages, which are described in the first step and covered in the API reference documentation. Therefore, understanding how to find the required information is an important step in the development process. Reference libraries use several techniques to organize content to make it easier to browse.

You can access the iOS reference library from the apple developer website or from Xcode. You can select help> developer documentation in Xcode to display the XCode document window on the screen. This window is the core of iOS development information. You can browse documents and perform searches, and add bookmarks for documents that may be read later. Each document has already been categorized by its content, which can facilitate updates and make the search scope more accurate to relevant documents.

When you install the iPhone SDK, Xcode automatically installs a document set containing the iOS reference library for you. XCode will automatically download document updates for you, but you can cancel this action in preference settings .) The iOS Reference Library contains a lot of information. Therefore, it is of great significance to understand its typographical design. Figure 1-3 shows the master of the Reference Library in the Xcode document window. The toolbar at the top of the page contains the search box and buttons, which can be used to navigate to other installed document sets or created bookmarks. You can browse documents by topic, framework, or other resource types you are looking for, or use a filter to control the document list to reduce the displayed document set.

Figure 1-3 iOS Reference Library

Important:IOSThe content of the Reference Library may not be up-to-date.IPhoneDevelopment Center http://www.apple.com.cn/developer/iphone) Visit the latest documents, release minutes, technical minutes, technology, technology Q & A and sample code. All documents are in HTML format, and most of them are in PDF format.

The Reference Library provides a large amount of information, which is very troublesome when writing code. To Help you quickly find specific information, XCode provides you with the Quick Help Window 1-4. This window displays information related to a specified symbol, including its syntax, description, and SDK version that can use the symbol. In addition, this window displays the relevant documentation and sample code of the symbol. Click the link in the window to access the corresponding resources in the reference library. To display the Quick Help window, press and hold the Option key and double-click a symbol in the Xcode editing window.

Figure 1-4 Quick help window in Xcode

Summary:IOSBefore development, you must read the content of this document. I hope this article will help you!