Android 框架简介

======================= 第一节 ===========================

这里简单的介绍了Android的java环境基础，在后面一节中会结合具体的实例来理解这一节的内容。

一、Dalvik虚拟机

Dalvik是Android的程序的java虚拟机，代码在dalvik/下，

./

|-- Android.mk

|-- CleanSpec.mk

|-- MODULE_LICENSE_APACHE2

|-- NOTICE

|-- README.txt

|-- dalvikvm 虚拟机的实现库

|-- dexdump

|-- dexlist

|-- dexopt

|-- docs

|-- dvz

|-- dx

|-- hit

|-- libcore

|-- libcore-disabled

|-- libdex

|-- libnativehelper 使用JNI调用本地代码时用到这个库

|-- run-core-tests.sh

|-- tests

|-- tools

`-- vm

二、Android的java框架

Android层次中第3层是java框架，第四层就是java应用程序。

Android的java类代码，主要是在frameworks/base/core/java/下，

./

|-- Android

|-- com

|-- jarjar-rules.txt

`-- overview.html

我们再看一下frameworks/base/目录

./

|-- Android.mk

|-- CleanSpec.mk

|-- MODULE_LICENSE_APACHE2

|-- NOTICE

|-- api

|-- awt

|-- build

|-- camera

|-- cmds

|-- common

|-- core

|-- data

|-- docs

|-- graphics

|-- include

|-- keystore

|-- libs

|-- location

|-- media

|-- native

|-- obex

|-- opengl

|-- packages

|-- preloaded-classes

|-- sax

|-- services

|-- telephony

|-- test-runner

|-- tests

|-- tools

|-- vpn

`-- wifi

这里也有Android的java框架代码。

三、JNI

在Android中，通过JNI，java可以调用C写的代码，主要的实现是在frameworks/base/core/jni，通过查看Android.mk，我们可以看到最后生成了libandroid_runtime.so，具体实现JNI功能需要上面我们介绍的libnativehelper.so，

四、系统服务之java

1、binder，提供Android的IPC功能

2、servicemanager，服务管理的服务器端

3、系统进程zygote，负责孵化所有的新应用

======================= 第二节 ==========================

在我平时工作中主要是进行linux网络子系统的模块开发、linux应用程序(C/C++)开发。在学习和从事驱动模块开发的过程中，如果你对linux系统本身，包括应用程序开发都不了解，那么读内核代码就如同天书，毫无意义，所以我分析框架也是从基本系统api开始的，当然也不会太多涉及到应用程序开发。

好，开始这节主要是讲一个简单的adnroid应用程序，从应用程序出发，到框架代码。

分析的应用程序我们也奉行拿来主义:froyo/development/samples/HelloActivity

./

|-- Android.mk

|-- AndroidManifest.xml

|-- res

|-- src

`-- tests

其他的就多说了，看代码

/**

* Copyright (C) 2006 The Android Open Source Project

*

* Licensed under the Apache License, Version 2.0 (the License);

* you may not use this file except in compliance with the License.

* You may obtain a copy of the License at

*

* http://www.apache.org/licenses/LICENSE-2.0

*

* Unless required by applicable law or agreed to in writing, software

* distributed under the License is distributed on an AS IS BASIS,

* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

* See the License for the specific language governing permissions and

* limitations under the License.

*/

package Android.util;

import com.Android.internal.os.RuntimeInit;

import java.io.PrintWriter;

import java.io.StringWriter;

/**

* API for sending log output.

*

*

Generally, use the Log.v() Log.d() Log.i() Log.w() and Log.e()

* methods.

*

*

The order in terms of verbosity, from least to most is

* ERROR, WARN, INFO, DEBUG, VERBOSE. Verbose should never be compiled

* into an application except during development. Debug logs are compiled

* in but stripped at runtime. Error, warning and info logs are always kept.

*

*

Tip: A good convention is to declare a TAG constant

* in your class:

*

*

private static final String TAG = MyActivity;

*

* and use that in subsequent calls to the log methods.

*

*

*

Tip: Don't forget that when you make a call like

*

Log.v(TAG, index= + i);

* that when you're building the string to pass into Log.d, the compiler uses a

* StringBuilder and at least three allocations occur: the StringBuilder

* itself, the buffer, and the String object. Realistically, there is also

* another buffer allocat