Android Note (57) Android Summary: Basic article

What is Android

Android is a free and open source Linux-based operating system that is used primarily for mobile devices such as smartphones and tablets, led and developed by Google and the Open Cell Alliance. The current release is 6.0

Advantages of the Android platform

First, openness
On the edge, the Android platform is the first development, the platform to allow any mobile terminal manufacturers to join the Android Alliance. Significant openness makes it possible to have more developers, and as users and applications become richer, a new platform will soon mature.
Ii. Break free from the bondage of operators
In the past for a long time, especially in Europe and the United States, mobile phone applications are often restricted by operators, the use of what features access to what network, almost all by the operator control. Since the launch of the iphone, users have been able to connect more easily to the network, reducing operator constraints. With the edge, HSDPA these 2G to 3G mobile network gradual transition and promotion, mobile phone random access to the network is not the operator in the mouth of the joke.
Three, the rich choice of hardware
This is also related to the openness of the Android platform, due to the openness of Android, many manufacturers will be introduced strange, functional features of various products. Functional differences and features, but does not affect the synchronization of data, and even software compatibility. It's like you're switching from Nokia Symbian-style to Apple's iphone, and you can easily transfer the best software from Symbian to your iphone, contacts and more.
Iv. developers not subject to any restrictions
The Android platform provides a very broad, free environment for third-party developers. So will not be affected by a variety of rules and regulations, we can imagine how many new and unique software will be born. But there are also two sides, the bloody, violent, erotic aspects of the program and games as controllable is one of the puzzles left to Android.
Five, seamless combination of Google Apps
Now Google, hoot astonished the Internet, has passed its 10 history. From search giants to comprehensive internet penetration, Google services such as maps, mail, search and so on have become an important link between users and the Internet, and Android platform phones will seamlessly combine these excellent Google services.

Android's architecture

Android can be roughly divided into four-tier architectures and five areas:

1.Linux Core Layer

The Android system is based on the Linux2.6 core, providing the underlying driver for a variety of hardware.

2. System Runtime Layer

This layer provides, for example, the main feature support for Android systems through a number of C + + libraries, such as the SQLite library that provides database spending, opengl| The ES Library provides support for 3D drawings, the WebKit library provides a browser kernel, and so on.

Also on this tier is the Android runtime, which mainly provides core libraries that allow developers to write Android apps in the Java language, and the Android runtime also contains Dalvik virtual machines. It allows each Android app to run in a separate process and has its own Dalvik virtual machine instance, optimized for mobile memory, CPU, etc. compared to a Java virtual machine, and is specifically tailored to the Dalvik.

3. Application Framework Layer

This layer mainly provides the various APIs that may be used to build the application

4. Application Layer

All applications installed on the phone belong to this layer.

Android Engineering Catalog

After the project is completed, the directories and files are generated:

src : The Java source code that holds the project.

Gen: automatically generated by the system, there is a R.java file, and the resources we add in the project generate an ID in this file.

Assets : Store Some files packaged with the program, the contents of these files can be read dynamically while the program is running, and the resources inside it will not generate IDs in R.java.

Bin: the file generated automatically at compile time.

Libs : third-party jar packages

Res :

drawable-hdpi , drawable-ldpi , drawable-mdpi , drawable-xhdpi , drawable-xxhdpi:

(1) drawable-hdpi contains high-resolution images, such as WVGA (480x800), FWVGA (480x854)

(2) drawable-mdpi contains medium-resolution images, such as HVGA (320x480)

(3) drawable-ldpi contains low-resolution images, such as QVGA (240x320)

ldpi:240x320

mdpi:320x480

hdpi:480x800, 480x854

XHDPI: At least 960*720

xxhdpi:1280x720

The system will be based on the machine's resolution to each of these folders to find the corresponding picture

Layout : Storing layout files

Menu : used to define the contents of the Application menu

values: Storing string contents

dimens.xml Storage size content, can access the corresponding resources through R.dimens

Strings.xml holds some text strings that can be accessed through r.string to the application's resources

style.xml defines the format and appearance of UI elements that can be accessed through the R.style class

Androidmanifest.xml : The entire project configuration file, the four components of the program, as well as permissions, compatible versions, target versions and other content need to be declared here

project.properties : Specifies the version of the SDK to use when compiling the program

Android compilation process

Write A. java file → write A. java file to generate the. class file → convert. class files to DAVLIKVM supported. dex files → package. Dex as an unsigned. apk file → sign an unsigned. apk file

Android System Boot process:

Refer to blog post: Android system boot process

Android App startup process

Reference Blog: Android application launch process source code analysis

Android Note (57) Android Summary: Basic article