Context框架
Context框架
Android程序Context的数量= Activity + Service + Application
ContextThemeWrapper、ContextWrapper功能委托给ContextImpl实现；
1. ContextImpl::getSystemService
public Object getSystemService(String name) {
return SystemServiceRegistry.getSystemService(this, name);
}
public String getSystemServiceName(Class<?> serviceClass) { // 2
return SystemServiceRegistry.getSystemServiceName(serviceClass);
}
2. SystemServiceRegistry::getSystemService
public static Object getSystemService(ContextImpl ctx, String name) {
ServiceFetcher<?> fetcher = SYSTEM_SERVICE_FETCHERS.get(name);
return fetcher != null ? fetcher.getService(ctx) : null;
}
public static String getSystemServiceName(Class<?> serviceClass) {
return SYSTEM_SERVICE_NAMES.get(serviceClass); // 4
}
3. SystemServiceRegistry::SYSTEM_SERVICE_NAMES初始化
static {
...
registerService(Context.ACTIVITY_SERVICE, ActivityManager.class,
new CachedServiceFetcher<ActivityManager>() {
@Override
public ActivityManager createService(ContextImpl ctx) {
return new ActivityManager(ctx.getOuterContext(), ctx.mMainThread.getHandler());
}});
...
}
static块，会在类被加载的时候执行且仅会被执行一次，一般用来初始化静态变量和调用静态方法。
4. SystemServiceRegistry::registerService
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);
}
5. SystemServiceRegistry::SYSTEM_SERVICE_FETCHERS 保存服务引用且final
// Service registry information.
// This information is never changed once static initialization has completed.
private static final HashMap<String, ServiceFetcher<?>> SYSTEM_SERVICE_FETCHERS =
new HashMap<String, ServiceFetcher<?>>();
private static final HashMap<Class<?>, String> SYSTEM_SERVICE_NAMES =
new HashMap<Class<?>, String>();
