Introduction to Android operating system
1.1 Android nouns
- The original meaning of the word Android refers to "robot", and it is also
the name of an open source mobile phone operating system based on the Linux platform announced by Google on November 5, 2007. The platform consists of an operating system, middleware, user interface and application software. - The word Android first appeared in the science
fiction novel "L'ève future" (L'ève future) published in 1886 by the French writer Auguste Villiers de l'Isle-Adam (Auguste Villiers de l'Isle-Adam) . He named the human-like machine Android.
1.2 Logo
- The Android logo was designed by the Ascender company, born in 2010, its design inspired by the view of men and women on the toilet door
-shaped symbol, so Brock draws a simple robot, its trunk shaped like tin cans, head There are also two antennas on it, and the Android robot is born
02. Development History
2.1 Introduction
- In October 2003, Andy Rubin and others founded the Android company and formed the Android team.
- On August 17, 2005, Google low-key acquired Android and its team, a high-tech enterprise that was only 22 months old. Andy Rubin became the vice president of Google's engineering department and continued to be responsible for the Android project.
- In 2008, at the Google I/O conference, Google proposed the AndroidHAL architecture diagram. On August 18 of the same year, Android
was approved by the Federal Communications Commission (FCC). In September 2008, Google officially released the Android 1.0 series.
This is also the earliest version of the Android system. - In September 2009, Google released the official version of Android 1.6, and launched a mobile phone equipped with the official version of Android 1.6
- HTC Hero (G3), with its excellent design and the new Android 1.6 operating system, HTC
Hero (G3) became the most popular mobile phone in the world at that time. Android 1.6 also has an interesting dessert name, it is called Donut (doughnut).
Update the version every year... - In 2019, Android 10. . . . . .
3. Release version
- 10.0 Android 10.0 In 2019, the official name of this year's Android Q is Android 10.
- 11 As usual, Android 11 may be released in March 2020 (development version), officially released at the Google I/O conference.
04. Architecture
Adopts a layered architecture
Android system architecture diagram, as follows
Linux kernel
- The foundation of the Android platform is the Linux kernel. For example, Android Runtime (ART) relies on the Linux kernel to perform low-level functions
such as threads and low-level memory management. Using the Linux kernel allows Android to take advantage of major security features, and allows device manufacturers to develop hardware drivers for the well-known kernel,
hardware abstraction layer (HAL) - Android's HAL (hardware abstraction layer) can provide hardware driver modules in closed source form. The purpose of HAL is to
separate the Android framework from the Linux kernel, so that Android does not rely too much on the Linux kernel to achieve
the concept of Kernel independent , and to allow the development of the Android framework to develop without considering the implementation of the driver.
Android Runtime - For devices running Android 5.0 (API level 21) or higher, each application runs in its own process and has its own
instance of Android Runtime (ART). ART is written to run multiple virtual machines on low-memory devices by executing DEX files. DEX files are a
bytecode format specially designed for Android. After optimization, they use very little memory. Compilation tool chain (such as Jack) compiles Java source code into DEX
bytecode, so that it can run native C/C++ libraries on the Android platform
- Many core Android system components and services (such as ART and HAL) are built from native code and require native libraries written in C and C++. The Android
platform provides Java framework APIs to show applications the functions of some of the native libraries. For example, you can
access OpenGL ES through the Java OpenGL API of the Android framework to support drawing and manipulating 2D and 3D graphics in the application. If you are developing an application that requires C or C++ code, you can use the
Android NDK to access some native platform library
Java API framework directly from the native code.
You can use the entire feature set of Android OS through APIs written in Java language. These APIs form the creation of Android applications - With the required building blocks, they can simplify the reuse of core modular system components and services including the following components and services
system applications
- Android comes with a set of core applications for email, text messaging, calendar, internet browsing, contacts, etc.
The apps that come with the platform are the same as the apps that users can choose to install, with no special status. Therefore, third-party applications can become the user's default web browser, SMS Messenger
or even the default keyboard (with some exceptions, such as the system's "Settings" application). System applications can be
used by users, as well as provide the main functions that developers can access from their own applications. For example, if your application wants to send text messages, you
don't need to build this function yourself . Instead , you can call the installed SMS application to send messages to the recipients you specify.
05 Application components
Android development four major component
activities (Activity)
- In Android, Activity is the foundation of all programs, and the flow of all programs runs in Activity. Activity can
be regarded as the most frequently encountered by developers and one of the most basic modules in Android. Generally, an Android application is composed of multiple activities
. Android applications between these multiple activities can jump to each other.
Service
- Service is a component in the android system, which is similar to the Activity level, but it cannot run by itself, it
can only run in the background, and can interact with other components. Service is a long life cycle code without an interface.
For example, open a music player program. If you want to go online at this time, then open the Android browser
. Although you have entered the browser program at this time, the song playback does not stop, but continues in the background.
Continue playing one after another. In fact, this playback is controlled by the Service that plays music.
Broadcast Receiver (BroadcastReceiver)
- In Android, Broadcast is a widely used mechanism for transferring information between applications.
Content Provider
- Content Provider is a third-party application data access solutions provided by Android
in Android, data protection is very strict, in addition to data on the SD card, an application data held by
libraries, files, etc., are No other direct access is allowed. Of course, Android does not really make every application an
island. It prepares a window for all applications. This is the Content Provider.
06 Platform advantages
Development
- In terms of advantages, the Android platform is first of all its openness, and the developed platform allows any mobile terminal manufacturer to join the Android
Alliance. Significant openness can enable it to have more developers. As users and applications become more abundant, a brand-new platform will soon mature.
Openness is conducive to the accumulation of popularity for the development of Android. Popularity here includes consumers and manufacturers. For consumers
, the biggest benefit is the abundant software resources. An open platform will also bring greater competition. In this way, consumers will be able to buy their favorite mobile phones at a lower price.
Rich hardware
- This point is still related to the openness of the Android platform. Due to the openness of Android, many manufacturers will launch
a variety of products with various functions and features. The functional differences and features will not affect data synchronization or even software compatibility, just like
switching from a Nokia Symbian style phone to an Apple iPhone, and at the same time, you can also bring the excellent software in Symbian to the iPhone
for use, contacts, etc. Data can be transferred easily.
Convenient development
- The Android platform provides third-party developers with a very broad and free environment that will not be hindered by all kinds of restrictions. It is
conceivable that how many novel and unique software will be born. But there are also two sides. How to control bloody, violent, and erotic programs and games is one of the problems left to Android.
Google app
- Google on the Internet has gone through 10 years of history. From a search giant to a comprehensive Internet penetration, Google services such as maps,
mail, search, etc. have become an important link between users and the Internet, and Android platform mobile phones will seamlessly combine these excellent Google services.