Android 框架簡介

======================= 第一節 ===========================

這里簡單的介紹了Android的java環境基礎，在后面一節中會結合具體的實例來理解這一節的內容。

一、Dalvik虛擬機

Dalvik是Android的程序的java虛擬機，代碼在dalvik/下，

./

|-- Android.mk

|-- CleanSpec.mk

|-- MODULE_LICENSE_APACHE2

|-- NOTICE

|-- README.txt

|-- dalvikvm 虛擬機的實現庫

|-- dexdump

|-- dexlist

|-- dexopt

|-- docs

|-- dvz

|-- dx

|-- hit

|-- libcore

|-- libcore-disabled

|-- libdex

|-- libnativehelper 使用JNI調用本地代碼時用到這個庫

|-- run-core-tests.sh

|-- tests

|-- tools

`-- vm

二、Android的java框架

Android層次中第3層是java框架，第四層就是java應用程序。

Android的java類代碼，主要是在frameworks/base/core/java/下，

./

|-- Android

|-- com

|-- jarjar-rules.txt

`-- overview.html

我們再看一下frameworks/base/目錄

./

|-- 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

這里也有Android的java框架代碼。

三、JNI

在Android中，通過JNI，java可以調用C寫的代碼，主要的實現是在frameworks/base/core/jni，通過查看Android.mk，我們可以看到最后生成了libandroid_runtime.so，具體實現JNI功能需要上面我們介紹的libnativehelper.so，

四、系統服務之java

1、binder，提供Android的IPC功能

2、servicemanager，服務管理的服務器端

3、系統進程zygote，負責孵化所有的新應用

======================= 第二節 ==========================

在我平時工作中主要是進行linux網絡子系統的模塊開發、linux應用程序(C/C++)開發。在學習和從事驅動模塊開發的過程中，如果你對linux系統本身，包括應用程序開發都不了解，那么讀內核代碼就如同天書，毫無意義，所以我分析框架也是從基本系統api開始的，當然也不會太多涉及到應用程序開發。

好，開始這節主要是講一個簡單的adnroid應用程序，從應用程序出發，到框架代碼。

分析的應用程序我們也奉行拿來主義:froyo/development/samples/HelloActivity

./

|-- Android.mk

|-- AndroidManifest.xml

|-- res

|-- src

`-- tests

其他的就多說了，看代碼

/**

* 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 allocation and copy, and even more pressure on the gc.

* That means that if your log message is filtered out, you might be doing