Android 各种Manager实例的创建

具体实现类 base/core/java/android/app/ContextImpl.java

里面含有静态代码块，registerService(SENSOR_SERVICE, new ServiceFetcher() {
                  public Object createService(ContextImpl ctx) {
                      return new SystemSensorManager(ctx.mMainThread.getHandler().getLooper());
                  }});

各种实例都在其中，主要是通过Map来集中管理，

        private static final HashMap<String, ServiceFetcher> SYSTEM_SERVICE_MAP =
 268             new HashMap<String, ServiceFetcher>();
 269
 270     private static int sNextPerContextServiceCacheIndex = 0;
 271     private static void registerService(String serviceName, ServiceFetcher fetcher) {
 272         if (!(fetcher instanceof StaticServiceFetcher)) {
 273             fetcher.mContextCacheIndex = sNextPerContextServiceCacheIndex++;
 274         }
 275         SYSTEM_SERVICE_MAP.put(serviceName, fetcher);
 276     }

   @Override
1478     public Object getSystemService(String name) {
1479         ServiceFetcher fetcher = SYSTEM_SERVICE_MAP.get(name);
1480         return fetcher == null ? null : fetcher.getService(this);
1481     }

              fetch.getService会调用createService，然后直接返回 代码如下

 public Object getService(ContextImpl ctx) {
 215             ArrayList<Object> cache = ctx.mServiceCache;
 216             Object service;
 217             synchronized (cache) {
 218                 if (cache.size() == 0) {
 219                     // Initialize the cache vector on first access.
 220                     // At this point sNextPerContextServiceCacheIndex
 221                     // is the number of potential services that are
 222                     // cached per-Context.
 223                     for (int i = 0; i < sNextPerContextServiceCacheIndex; i++) {
 224                         cache.add(null);
 225                     }
 226                 } else {
 227                     service = cache.get(mContextCacheIndex);
 228                     if (service != null) {
 229                         return service;
 230                     }
 231                 }
 232                 service = createService(ctx);
 233                 cache.set(mContextCacheIndex, service);
 234                 return service;
 235             }
 236         }

 

          获取的时候直接在SYSTEM_SERVICE_MAP取出来，

    @Override
1478     public Object getSystemService(String name) {
1479         ServiceFetcher fetcher = SYSTEM_SERVICE_MAP.get(name);
1480         return fetcher == null ? null : fetcher.getService(this);
1481     }