Android hierarchy and Analysis

1. Android is divided into four layers:

ApplicationProgramApplications, application framework, libraries and Android runtime, and Linux kernel ).

2. Application Layer:

All applications are written in Java by calling the APIS provided by the application framework.

3. Application Framework layer:

It provides developers with an API framework for full access to core applications.

• Activity MANAGER: manages application lifecycles and provides common navigation rollback functions. For example, you need to enable the resources required by the application and release the resources required when you exit the application.

• Window Manager: manages all opened window programs.

• Content Providers: allow applications to access or share data of another application, such as a contact database.

• View system: it can be used to build applications, including list, grid, text box, button, and drawing, as well as embedded web browsers.

• Notification MANAGER: enables the application to display custom prompts in the status bar.

• Package Manager: manages all applications installed on Android. For example, viewing information and uninstalling programs.

• Resource Manager: provides various resource providers. For example, character resources, image resources, and audio resources.

• Hardware services: call and answer functions, map management functions, Bluetooth functions, WiFi functions, USB functions, and sensor services.

4. System runtime database:

The system Runtime Library layer consists of the library and Android Runtime Library.

1) Library: Android contains some C/C ++ libraries that can be used by different components in the Android system. They provide services to developers through the application framework, core library features:

Surface MANAGER: manages the display subsystem and provides seamless integration of 2D and 3D layers for multiple applications.

Media framework: Based on packetvideo opencore, this library supports playback and recording of audio and video in multiple formats, and supports static image files. The encoding formats include MPEG4, H.264, MP3, AAC, Amr, JPG, and PNG.

SQLite: lightweight relational database engine available and powerful for all applications

Opengles supports OpenGL es1.x and OpenGL ES 2.0. This library can use hardware 3D acceleration or highly optimized 3D soft acceleration.

FreeType: bitmap, vector, and font display

WebKit: The latest web browser engine that supports Android browsers and an embedded web server.

SSL: secure communication-related technical processing, a security protocol that provides security and data integrity for network communication.

LIBE: Android does not use glibc as the C library, but uses the bionic lib developed by Google. It inherits the Standard C system function library from BSD and is specially tailored for Embedded Linux devices.

2) Android Runtime Library:

The android Runtime Library is divided into the core library and the Dalvik virtual machine. The core library provides most of the functions of the core library of the Java language. Here, the core Library provides the interface for calling the underlying Library to the application framework layer through JNI. The Dalvik virtual machine is implemented to run multiple VMS at the same time.

5. Linux kernel layer:

Android depends on the core system services provided by Linux kernel, such as security, memory management, process management, network stack, and driver module. Android enhances the kernel.