Android(安卓)Framework系统服务详解

Android Framework系统服务详解
操作环境系统：Linux (Ubuntu 12.04) 平台：高通
Android版本：5.1 PS: 符号...为省略N条代码
一、大致原理分析 Android本身有很多系统服务，如：AlarmManagerService、PowerManagerService、AudioService等，这些服务在手机系统启动时就进行开启或监听状态，由ServiceManager负责实例化运行。系统服务与本地新增的服务属于两个不同进程，必须通过AIDL(Android Interface Definition Language ：Android接口定义语言)进行跨进程通信
二、新增具体案例
2.1 创建AIDL接口文件
路径：frameworks/base/core/java/android/service/test/IMyTestManager.aidl

package android.service.test;interface IMyTestManager {    String sayHello();    int priFunction();}

2.2 将创建的AIDL加入编译中路径：frameworks/base/Android.mk

## READ ME: ############################################################ When updating this list of aidl files, consider if that aidl is## part of the SDK API.  If it is, also add it to the list below that## is preprocessed and distributed with the SDK.  This list should## not contain any aidl files for parcelables, but the one below should## if you intend for 3rd parties to be able to send those objects## across process boundaries.#### READ ME: ########################################################LOCAL_SRC_FILES += \...core/java/android/service/test/IMyTestManager.aidl \...

2.2.1 注释的大概意思：
当更新这个文件列表时,如果考虑aidl是SDK API的一部分。如果它是，同时添加到下面的列表进行预处理和分布式的SDK。这个列表不包含任何aidl文件parcelables接口。但是如果你想让第三方能够在整个过程发送这些对象的话，你就应该下面有一个的目标 2.2.2 LOCAL_SRC_FILES += \ 这个宏是编译管理AIDL的，很多系统AIDL在此添加进行编译 2.2.3 在frameworks/base/下用mm进行单编，把AIDL的java接口生成出来编译完成后检查路径： out/target/common/obj/JAVA_LIBRARIES/framework_intermediates/src/core/java/android/service/test/IMyTestManager.java
2.3 创建新的系统服务类
路径：frameworks/base/core/java/android/service/test/MyTestManagerService.java

public class MyTestManagerService extends IMyTestManager.Stub{    private static final String TAG = "MyTestManagerService";    private Context mContext;    public MyTestManagerService(Context context) {        mContext = context;    }    @Override    public String sayHello() throws RemoteException {        // TODO Auto-generated method stub        Log.d(TAG, "sayHello()");        return "Hello AIDL";    }        @Override    public int priFunction() throws RemoteException {        // TODO Auto-generated method stub        Log.d(TAG, "priFunction()");        return 0;    }}

2.4 创建系统服务公开接口管理类
路径：frameworks/base/core/java/android/service/test/MyTestManager.java

public class MyTestManager {    private static final String TAG = "MyTestManager";    private IMyTestManager mService;    public MyTestManager(IMyTestManager service) {        mService = service;    }    public String sayHello() throws RemoteException {        Log.d(TAG, "sayHello()");        return mService.sayHello();    }}

2.4.1 Android系统中很多系统服务API没有全部公开，都是在Frameworks层通过Manager类封装一层来进行管理公开接口。也就是说对Application层公开都是通过Manager封装来决定的，这里我只公开了sayHello()。priFunction()是我故意不公开的，方便理解

2.5 将创建的服务添加进ServiceManager 路径：frameworks/base/services/java/com/android/server/SystemServer.java

private void startOtherServices() {    ...    AudioService audioService = null;    MyTestManagerService mTestService = null;    ...    if (!disableMedia && !"0".equals(SystemProperties.get("system_init.startaudioservice"))) {        try {            Slog.i(TAG, "Audio Service");            audioService = new AudioService(context);            ServiceManager.addService(Context.AUDIO_SERVICE, audioService);        } catch (Throwable e) {            reportWtf("starting Audio Service", e);        }    }    ...    try {        Slog.i(TAG, "MyTestManager Service");        mTestService = new MyTestManagerService(context);        ServiceManager.addService(Context.MYTEST_SERVICE, mTestService);    } catch (Throwable e) {        reportWtf("starting MyTestManager", e);    }    ...}

2.5.1 为了阅读思路清晰，我保留了AudioService的服务添加代码。至于if条件，我们也可以添加，java里面控制的话可以在config.xml中定义bool类型，一般是为了区分多个项目的差异。涉及到项目的overlay，可根据操作项目的具体需求来进行。驱动底层一般都是宏控，稍微提一下。 2.5.2 代码中的Context.MYTEST_SERVICE服务常量添加路径：frameworks/base/core/java/android/content/Context.java

.../*** Use with {@link #getSystemService} to retrieve a* {@link android.media.AudioManager} for handling management of volume,* ringer modes and audio routing.** @see #getSystemService* @see android.media.AudioManager*/public static final String AUDIO_SERVICE = "audio";public static final String MYTEST_SERVICE = "mytest";...

2.6 注册服务
路径：frameworks/base/core/java/android/app/ContextImpl.java

static {    ...    registerService(AUDIO_SERVICE, new ServiceFetcher() {        public Object createService(ContextImpl ctx) {            return new AudioManager(ctx);        }    });        registerService(MYTEST_SERVICE, new ServiceFetcher() {        public Object createService(ContextImpl ctx) {            IBinder iBinder = ServiceManager.getService(Context.MYTEST_SERVICE);                if (iBinder == null) {                    return null;                }                IMyTestManager service = IMyTestManager.Stub                    .asInterface(iBinder);                return new MyTestManager(service);            }    });    ...}

2.6.1 在这里可以看到明显的对比，有一个差异就是AudioManager在注册服务的时候并没有像我添加的一样将服务传给IBinder，再通过IBinder来进行接口对接获取到服务。其实，AudioManger已经在内部类做了这层封装，原理是一样的，也有很多系统服务采用我这种方式进行注册。附AudioManager部分源码：路径：frameworks/base/media/java/android/media/AudioManager.java

public class AudioManager {    ...    private static IAudioService sService;    /**     * @hide     */    public AudioManager(Context context) {        mContext = context;        ...    }    private static IAudioService getService()    {        if (sService != null) {            return sService;        }        IBinder b = ServiceManager.getService(Context.AUDIO_SERVICE);        sService = IAudioService.Stub.asInterface(b);        return sService;    }    ...}

2.7 调用新增的系统服务

MyTestManager mTestManager = (MyTestManager) getSystemService(Context.MYTEST_SERVICE);try {    //这里调用不出priFunction()，MyTestManager没有对它进行再次封装    mTestManager.sayHello();} catch (RemoteException e) {    // TODO Auto-generated catch block    e.printStackTrace();}

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