[Entry 4] Android core modules and related technologies

Source: Internet
Author: User
Tags vector font
Android is a mobile device platform. Its software hierarchy includes an operating system (OS), middleware (middleware), and applications. Program (Application ). Based on the software block diagram of Android, the software hierarchy is divided into the following layers: 1. operating system layer (OS)
2. Various libraries and Android runtime Environments)
3. Application Framework)
4. Application)
The following describes the key points of andoid software and related technologies:
● Operating system layer (OS)
Android uses linux2.6 as the operating system. linux2.6 is a standard technology, and Linux is also an open operating system. Android's use of the operating system includes the core and the driver. Android's Linux core is the standard linux2.6 kernel, and Android requires more drivers related to mobile devices. The main driver is as follows:
Display Driver ):
Frame Buffer Driver Based on Linux
Keyboard driver ):
As the keyboard driver of the Input Device
Flash Memory DRIVER ):
MTD-based Flash Driver
Camera DRIVER ):
Commonly used Linux-based v4l2 (video for Linux) drivers.
Audio driver ):
Commonly used Driver Based on ALSA (Advanced Linux sound architecture, advanced Linux sound system)
Bluetooth driver ):
Wireless transmission technology based on IEEE 802.15.1 Standard
WiFi Driver (camera driver ):
Driver Based on IEEE 802.11 standard
Binder ipc driver:
Andoid is a special driver with a separate device node that provides inter-process communication.
Power Management)
● Various libraries and Android runtime Environments)
This level corresponds to a General Embedded System, which is equivalent to a middleware level. Android has two levels: one is a variety of libraries and the other is the android runtime environment. Content of this layer
Mostly implemented using C ++.
Among them, various libraries include:
C: The standard library of C language, which is also the most underlying library in the system. C library is implemented through Linux system calls.
Media framework (mediaframeword): This part is the core of Android multimedia. Based on opencore of packetvideo (PV), this library provides a total of functions.
There are two major parts: the playback of audio and video, and the recorder of audio and video ).
SGL: 2D image engine.
SSL: the Secure Socket Layer is located between the TCP/IP protocol and various application layer protocols, providing security support for data communication.
OpenGL ES 1.0: This section provides 3D support.
Surface management: This section provides functions for the management and display subsystem.
SQLite: A General Embedded Database
WebKit: core of Web browsers
FreeType: bitmap and vector font functions.
Android libraries are generally provided in the form of system middleware. A notable feature of these libraries is that they are closely related to the applications of mobile device platforms.
The android runtime environment mainly refers to the virtual machine technology Dalvik. The Dalvik virtual machine is different from the general Java Virtual Machine (Java VM). It does not execute the java standard bytecode but the execution file in the Dalvik executable format (. Dex. During execution, each application is a process (a process in Linux ). The biggest difference between the two is that Java VMS are stack-based virtual machines, while Dalvik is register-based ). Obviously, the biggest advantage of the latter is that it can achieve greater Optimization Based on hardware, which is more suitable for the characteristics of mobile devices.
● Application Framework)
The Android Application Framework provides APIs for developers at the application layer. It is actually an application framework. Because the upper-layer applications are built in Java
Layers first contain the various controls required by the UI program:
For example, views (view components) include lists, grids, text boxes, and buttons. Even an embedded web browser.
An andoid application can take advantage of the following parts in the application framework:
Activity)
Broadcast intent receiver (broadcast intent receiver)
Service)
Content Provider)
● Application)
Android applications mainly involve user interfaces, which are usually written in Java and can contain various resource files (stored in the res directory) after the Java program and related resources are compiled, an APK package is generated. Android provides many core applications such as home, contact, phone, and browser. At the same time, application developers can use APIs at the application framework layer to implement their own applications. This is also a manifestation of the huge potential of Android open source.

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