Android Architecture

Android Framework Libraries

  Next on the stack are the Android framework libraries, sometimes called just “the framework.” The framework includes all Java libraries that are not part of the standard Java runtime (java., javax., and so on) and is for the most part hosted under the android top-level package. The framework includes the basic blocks for building Android applications, such as the base classes for activities, services, and content providers (in the android.app.* packages); GUI widgets (in the android.view.* and android.widget packages); and classes for file and database access (mostly in the android.database.* and android.content.* packages). It also includes classes that let you interact with device hardware, as well as classes that take advantage of higher-level services offered by the system.

  Android framework 依赖通常被称为 framework，包括所有JAVA 依赖包，区别于标准Java runtime（java., javax.,等等 ），大部分是低于android 最高层的包。framework 包括Android 应用构建的很多基本的区域，例如四大组件，activity，service，content provide（以 android.app.* 包名）等的基类；GUI 组件（以android.view.* and android.widget的包名）和文件、数据库类（大部分以android.database.* and android.content.* 包名）。同时包含与硬件连接类和系统服务的高级services

  Even though almost all Android OS functionality above the kernel level is implemented as system services, it is not exposed directly in the framework but is accessed via facade classes called managers. Typically, each manager is backed by a corresponding system service; for example, the BluetoothManager is a facade for the BluetoothManagerService.

  虽然系统服务是Android OS 函数在核心功能，但是他们不会直接暴漏在framework层，而是通过一个管理类去通信。有代表性是，每一个管理者都会被相当于系统服务作为依赖，例如BluetoothManager 代表是 BluetoothManagerService.

System Services

   The layers introduced up until now make up the plumbing necessary to implement the core of Android—system services. System services (79 as of version 4.4) implement most of the fundamental Android features, including display and touch screen support, telephony, and network connectivity. Most system services are implemented in Java; some fundamental ones are written in native code.

   系统服务是Android核心，引入很多基本Android 特性，包括显示、屏幕触摸、电话、网络连接。很多系统服务属于java 层，一部分属于native层。

   With a few exceptions, each system service defines a remote interface that can be called from other services and applications. Coupled with the service discovery, mediation, and IPC provided by Binder, system services effectively implement an object-oriented OS on top of Linux.

   一些特殊，这些系统服务被定义为一个远程接口为其他服务和应用调用，通过Binder 对服务解耦、调解，通信，系统服务被引入作为Linux顶层系统