Android系统源码之LocalServices

最新推荐文章于 2025-06-05 16:09:55 发布

原创最新推荐文章于 2025-06-05 16:09:55 发布 · 931 阅读

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#android #java

LocalServices类在Android框架中用于缓存系统服务实例，它使用ArrayMap存储服务对象，仅在系统进程中可用。服务在onStart时注册到LocalServices，通过getService获取。此机制简化了系统内部服务之间的调用。

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这个文件位于frameworks/base/core/java/com/android/server/LocalServices.java
代码也非常简单，就是用一个ArrayMap去缓存service实例

/**
 * This class is used in a similar way as ServiceManager, except the services registered here
 * are not Binder objects and are only available in the same process.
 *
 * Once all services are converted to the SystemService interface, this class can be absorbed
 * into SystemServiceManager.
 *
 * {@hide}
 */
public final class LocalServices {
    private LocalServices() {}

    private static final ArrayMap<Class<?>, Object> sLocalServiceObjects =
            new ArrayMap<Class<?>, Object>();

    /**
     * Returns a local service instance that implements the specified interface.
     *
     * @param type The type of service.
     * @return The service object.
     */
    @SuppressWarnings("unchecked")
    public static <T> T getService(Class<T> type) {
        synchronized (sLocalServiceObjects) {
            return (T) sLocalServiceObjects.get(type);
        }
    }

    /**
     * Adds a service instance of the specified interface to the global registry of local services.
     */
    public static <T> void addService(Class<T> type, T service) {
        synchronized (sLocalServiceObjects) {
            if (sLocalServiceObjects.containsKey(type)) {
                throw new IllegalStateException("Overriding service registration");
            }
            sLocalServiceObjects.put(type, service);
        }
    }

    /**
     * Remove a service instance, must be only used in tests.
     */
    @VisibleForTesting
    public static <T> void removeServiceForTest(Class<T> type) {
        synchronized (sLocalServiceObjects) {
            sLocalServiceObjects.remove(type);
        }
    }
}

全局搜索LocalServices.addService后可以发现，基本上在service的onStart的方法中会调用LocalServices.addService将自己缓存在LocalServices中。要使用的时候再调用getService取出来。
看注释能知道，这里面的service都要在系统进程中使用。这样缓存方便系统之间的服务调用。