基于Andoird 4.2.2的Account Manager源代码分析学习：AccountManager的简要工作流程

- 对于帐号管理，由接口IAccountManager描述其相关的一组行为
- AccountManagerService是Android的系统服务。它实现了接口IAccountManager定义的这一组行为。这些行为的实现依赖应用程序中定义的Authenticator。

- AccountManager是一个面向应用程序开发的组件。它提供一组对应于IAccountManager协议的应用程序接口。这组接口通过Binder机制与系统服务AccountManagerService进行通信，协作完成帐户相关的操作。同时，AccountManager接收应用程序提供的回调，以此在帐号操作完成之后向应用程序返回对应的结果，同时触发应用程序层对这个结果的处理。

以addAccount()操作为例，步骤如下:

1. AccountManager初始化一个匿名的AmsTask子类实例。AmsTask是AccountManager的内部类:

[java] private abstract class AmsTask extends FutureTask<Bundle> implements AccountManagerFuture<Bundle> {
    final IAccountManagerResponse mResponse;
    final Handler mHandler;
    final AccountManagerCallback<Bundle> mCallback;
    final Activity mActivity;
    public AmsTask(Activity activity, Handler handler, AccountManagerCallback<Bundle> callback) {
        super(new Callable<Bundle>() {
            public Bundle call() throws Exception {
                throw new IllegalStateException("this should never be called");
            }
        });

        mHandler = handler;
        mCallback = callback;
        mActivity = activity;
        mResponse = new Response();
    }
    ...

    private abstract class AmsTask extends FutureTask<Bundle> implements AccountManagerFuture<Bundle> {
        final IAccountManagerResponse mResponse;
        final Handler mHandler;
        final AccountManagerCallback<Bundle> mCallback;
        final Activity mActivity;
        public AmsTask(Activity activity, Handler handler, AccountManagerCallback<Bundle> callback) {
            super(new Callable<Bundle>() {
                public Bundle call() throws Exception {
                    throw new IllegalStateException("this should never be called");
                }
            });

            mHandler = handler;
            mCallback = callback;
            mActivity = activity;
            mResponse = new Response();
        }
        ...
它是一个FutureTask子类，执行异步的任务，并返回结果。
addAccount()中的匿名子类实现了AmsTask.doWork()方法:

[java] public AccountManagerFuture<Bundle> addAccount(final String accountType,
        final String authTokenType, final String[] requiredFeatures,
        final Bundle addAccountOptions,
        final Activity activity, AccountManagerCallback<Bundle> callback, Handler handler) {
    ...
    return new AmsTask(activity, handler, callback) {
        public void doWork() throws RemoteException {
            mService.addAcount(mResponse, accountType, authTokenType,
                    requiredFeatures, activity != null, optionsIn);
        }
    }.start();
}

    public AccountManagerFuture<Bundle> addAccount(final String accountType,
            final String authTokenType, final String[] requiredFeatures,
            final Bundle addAccountOptions,
            final Activity activity, AccountManagerCallback<Bundle> callback, Handler handler) {
        ...
        return new AmsTask(activity, handler, callback) {
            public void doWork() throws RemoteException {
                mService.addAcount(mResponse, accountType, authTokenType,
                        requiredFeatures, activity != null, optionsIn);
            }
        }.start();
    }

在doWork()方法的实现中，调用AccountManager持有的AccountManagerService的代理对象（mService）向AccountManagerService发起IPC。

2. AccountManger调用AmsTask匿名子类的start()方法启动任务。
3. start()方法会调用本类的doWork()方法，在这里就是执行AccountManagerService的addAccount()操作。
4. 根据FutureTask的实现机制，在任务执行的结束时期，会调用本类的done()方法。AmsTask类覆盖了这个方法:

[java] protected void done() {
    if (mCallback != null) {
        postToHandler(mHandler, mCallback, this);
    }
}

        protected void done() {
            if (mCallback != null) {
                postToHandler(mHandler, mCallback, this);
            }
        }
这里的实现调用了AccountManager.postHandler()方法。看名字就可以猜到，这里将mCallback回调对象里面的run()方法传送给主线程的handler进行调用:

[java] private void postToHandler(Handler handler, final AccountManagerCallback<Bundle> callback,
final AccountManagerFuture<Bundle> future) {
handler = handler == null ? mMainHandler : handler;

补充：移动开发 , Android ,