Android's system architecture detailed

What is Andriod?

First, as Dan Morrill, director of Android Open source and compatibility technology, explains in the Android Development manual compatibility section, "Android is not a specification or distribution version of the traditional Linux style, nor is it a series of reusable component integrations, Android is a piece of software used to connect devices. ”

What is Andriod?

Linux

The bottom of everything is a stable Linux kernel that stays updated (the Nexus I use now is the 2.6.32 kernel), and our elaborate energy management components, and of course, the extensions and common components that integrate them into the upper Linux code.

Dalvik

Another important part of Android, including virtual machines and an important set of operating environments. Its design is very ingenious, is a very good mobile phone terminal application of the bottom.

How does the code build?

The Dalvik virtual machine executes only. Dex's executable file. When the Java program is compiled, it will eventually need to be converted to a. dex format by using the tools in the SDK to perform on the virtual machine.

What I need to emphasize is that the Android app itself can be seen as code that runs on the platform and invokes APIs, so there's no need to pay special attention to how the code is generated.

Special apps.

Some of the apps that are based on Dalvik virtual machines appear to be part of Android, actually provided by Google, including dialer, Contacts, Calendar, Gmail and chat. The vast majority of them are open source and reusable. There are only a few exceptions, such as Google Maps and Android Market.

Open source, those things.

In the figure below, most of the green components are open source based on Apache licenses, with the rest based on the GPL, LGPL and BSD.

Open-Source Android

Android Framework

There's a lot of space on the Android Developer Network (developer.android.com) to help you use it, and you're not going to get tired of it.

Android Framework

Standard library

Here "standard" refers to "developers in the open source environment is generally available."

What's inside the app?

An Android app is contained in a compressed folder that we call APK, and apk has nothing to say, and it needs to be noted that the Android manifest--interface between the app and the Android system.

What's Inside the app (1)

What's Inside the app (2)

Other

Most applications are based on Dalvik, and I mean apps other than games. Game developers often want to write with C + + to exclude the use of virtual machines, so they can be developed through Andriod NDK.