一个简单的SystemService(vibrator)

Android 6.0
1:应用怎么使用vibrator
   Vibrator mVibrator = (Vibrator) getSystemService(Context.VIBRATOR_SERVICE);   //获取Vibrator实例
   mVibrator.vibrate(500);
   frameworks/base/core/java/android/app/SystemServiceRegistry.java

               public static Object getSystemService(ContextImpl ctx, String name) {
               ServiceFetcher<?> fetcher = SYSTEM_SERVICE_FETCHERS.get(name);
               return fetcher != null ? fetcher.getService(ctx) : null;

               } //获取Vibrator
               SYSTEM_SERVICE_FETCHERS是一个HashMap，通过我们服务的名字name字符串，从这个HashMap里取出一个ServiceFetcher，
               再return这个ServiceFetcher的getService()。ServiceFetcher是什么？它的getService()又是什么？
               既然他是从SYSTEM_SERVICE_FETCHERS这个HashMap里get出来的，那就找一找这个HashMap都put了什么。
               通过搜索SystemServiceRegistry可以找到如下代码：

               private static <T> void registerService(String serviceName, Class<T> serviceClass,
                   ServiceFetcher<T> serviceFetcher) {
               SYSTEM_SERVICE_NAMES.put(serviceClass, serviceName);
               SYSTEM_SERVICE_FETCHERS.put(serviceName, serviceFetcher);
               }
               调用
               final class SystemServiceRegistry {
               registerService(Context.VIBRATOR_SERVICE, Vibrator.class, //使用private static <T> void registerService
                   new CachedServiceFetcher<Vibrator>() {
               @Override
               public Vibrator createService(ContextImpl ctx) {
                   return new SystemVibrator(ctx);
               }};
               } //注册

   分析一： frameworks/base/core/java/android/os/Vibrator.java //Vibrator只是定义在android.os 包里的一个抽象类
       public abstract class Vibrator{
           abstract void cancel() 取消振动
           abstract boolean hasVibrator() 是否有振动功能
           abstract void vibrate(long[] pattern, int repeat) 按节奏重复振动
           abstract void vibrate(long milliseconds) 持续振动
       }
       方法在./frameworks/base/core/java/android/os/SystemVibrator.java中实现
       public class SystemVibrator extends Vibrator {
             private final IVibratorService mService; //IVibratorService在 frameworks/base/core/java/android/os/IVibratorService.aidl 实现

               public SystemVibrator(Context context) {
                   super(context);
                   mService = IVibratorService.Stub.asInterface(   //接口，
                   ServiceManager.getService("vibrator"));
               }


               public boolean hasVibrator() {                   //实现方法
                   return mService.hasVibrator();               //调用接口
               }
       }
   二：       IVibratorService在 frameworks/base/core/java/android/os/IVibratorService.aidl //接口定义，
               interface IVibratorService
               {
                   boolean hasVibrator();
                   void vibrate(int uid, String opPkg, long milliseconds, int usageHint, IBinder token);
                   void vibratePattern(int uid, String opPkg, in long[] pattern, int repeat, int usageHint, IBinder token);
                   void cancelVibrate(IBinder token);
               }
           接口定实现在./frameworks/base/services/core/java/com/android/server/VibratorService.java

JNI  ./frameworks/base/services/core/jni/com_android_server_VibratorService.cpp
               public class VibratorService extends IVibratorService.Stub
                       implements InputManager.InputDeviceListener {


               }
               可以看到 VibratorService实现了IVibratorService定义的所有接口，并通过JNI调用到native层，进行更底层的实现

三：VibratorService 是怎么成为系统服务的
   frameworks/base/services/java/com/android/server/SystemServer.java
       VibratorService vibrator = null;
       vibrator = new VibratorService(context); //实例化VibratorService并添加到ServiceManager
       ServiceManager.addService("vibrator", vibrator);

           try {
               vibrator.systemReady(); ////通知服务系统启动完成
           } catch (Throwable e) {
               reportWtf("making Vibrator Service ready", e);
           }

mService 相当于IVibratorService在应用层的一个代理，所有的实现还是在SystemServer的VibratorService里。
看代码时可以发现registerService是在static代码块里静态调用的，所以getSystemServcr获得的各个Manager也都是单例的

从上面的分析，我们可以总结出Vibrator服务的整个实现流程：

1：定义一个抽象类Vibrator，定义了应用中可以访问的一些抽象方法
   frameworks/base/core/java/android/os/Vibrator.java
   定义具体的类SystemVibrator继承Vibrator，实现抽象方法
   frameworks/base/core/java/android/os/SystemVibrator.java
2：定义一个AIDL接口文件IVibratorService，定义系统服务接口
   frameworks/base/core/java/android/os/IVibratorService.aidl
   定义服务VibratorService，实现IVibratorService定义的接口
   ./frameworks/base/services/core/java/com/android/server/VibratorService.java
   public class VibratorService extends IVibratorService.Stub
3：将VibratorServicey添加到系统服务
   frameworks/base/services/java/com/android/server/SystemServer.java
   VibratorService vibrator = null;
   vibrator = new VibratorService(context); //实例化VibratorService并添加到ServiceManager
   ServiceManager.addService("vibrator", vibrator);

       try {
           vibrator.systemReady(); ////通知服务系统启动完成
       } catch (Throwable e) {
           reportWtf("making Vibrator Service ready", e);
       }

4:在SystemVibrator中通过IVibratorService的代理连接到VibratorService，这样SystemVibrator的接口实现里就可以调用IVibratorService的接口：
frameworks/base/core/java/android/os/SystemVibrator.java

       public class SystemVibrator extends Vibrator {
               private final IVibratorService mService;

               public SystemVibrator(Context context) {
                   super(context);
                   mService = IVibratorService.Stub.asInterface(
                   ServiceManager.getService("vibrator"));
               }


               public boolean hasVibrator() {
                   return mService.hasVibrator();
               }
       }

5:在Context里定义一个代表Vibrator服务的字符串
   frameworks/base/core/java/android/content/Context.java
   public abstract class Context {

   public static final String VIBRATOR_SERVICE = "vibrator";
   }
   frameworks/base/core/java/android/app/SystemServiceRegistry.java //添加SystemVibrator的实例化过程

       final class SystemServiceRegistry {
       registerService(Context.VIBRATOR_SERVICE, Vibrator.class,
           new CachedServiceFetcher<Vibrator>() {
       @Override
       public Vibrator createService(ContextImpl ctx) {
           return new SystemVibrator(ctx);
       }});
       }
6 在应用中使用Vibrator的接口

Vibrator mVibrator = (Vibrator) getSystemService(Context.VIBRATOR_SERVICE);
mVibrator.vibrate(500);

//目前是2个问题，一个是要注册系统服务了 VibratorService 为什么还要在SystemServiceRegistry.java中实例化

一个简单的SystemService(vibrator)

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