基于Andoird 4.2.2的Account Manager源代码分析学习：创建选定类型的系统帐号

AccountManager.addAccount()

    public AccountManagerFuture<Bundle> addAccount(final String accountType,
            final String authTokenType, final String[] requiredFeatures,
            final Bundle addAccountOptions,
            final Activity activity, AccountManagerCallback<Bundle> callback, Handler handler) {
        ...
    }

在程序中创建指定类型的系统帐号，需要提供一个AccountManagerCallback类型的回调，后面会讲到其作用。

本方法要求用户添加指定类型的帐号。
此种帐号类型对应的authenticator将加载对应的UI来处理这个请求。
方法返回一个AccountManagerFuture对象，可解析出一个Bundle，包含以下信息：
- KEY_ACCOUNT_NAME: 创建的帐号的名称
- KEY_ACCOUNT_TYPE: 帐号类型

本方法创建一个匿名AmsTask实例并启动：

        return new AmsTask(activity, handler, callback) {
            public void doWork() throws RemoteException {
                mService.addAcount(mResponse, accountType, authTokenType,
                        requiredFeatures, activity != null, optionsIn);
            }
        }.start();

这里，以异步的方式请求AccountManagerService.addAccount()

start()方法立即返回，返回值是AccountManagerFuture类型的。

AccountManagerService.addAccount()

这个方法中，创建一个Session类型的匿名实例，并调用其bind()方法，最终捆绑到应用程序提供的authenticator service：

            new Session(accounts, response, accountType, expectActivityLaunch,
                    true /* stripAuthTokenFromResult */) {
                public void run() throws RemoteException {
                    mAuthenticator.addAccount(this, mAccountType, authTokenType, requiredFeatures,
                            options);
                }

                protected String toDebugString(long now) {
                    return super.toDebugString(now) + ", addAccount"
                            + ", accountType " + accountType
                            + ", requiredFeatures "
                            + (requiredFeatures != null
                              ? TextUtils.join(",", requiredFeatures)
                              : null);
                }
            }.bind();

这是Session.bind()方法的相关细节：

        void bind() {
            ...
            if (!bindToAuthenticator(mAccountType)) {
                Log.d(TAG, "bind attempt failed for " + toDebugString());
                onError(AccountManager.ERROR_CODE_REMOTE_EXCEPTION, "bind failure");
            }
        }

bindToAuthenticator()方法找到对应的组件名称（应用程序中定义的相关service），并且对Service发起绑定：

        private boolean bindToAuthenticator(String authenticatorType) {
            final AccountAuthenticatorCache.ServiceInfo<AuthenticatorDescription> authenticatorInfo;
            authenticatorInfo = mAuthenticatorCache.getServiceInfo(
                    AuthenticatorDescription.newKey(authenticatorType), mAccounts.userId);
            ...

            Intent intent = new Intent();
            intent.setAction(AccountManager.ACTION_AUTHENTICATOR_INTENT);
            intent.setComponent(authenticatorInfo.componentName);
            ...

            if (!mContext.bindService(intent, this, Context.BIND_AUTO_CREATE, mAccounts.userId)) {
                ...
            }

            return true;
        }

Session类实现了ServiceConnection接口，因此，当成功绑定到对应的应用程序中的Service，其实现的onServiceConnected()方法将被调用：

        public void onServiceConnected(ComponentName name, IBinder service) {
            mAuthenticator = IAccountAuthenticator.Stub.asInterface(service);
            try {
                run();
            } catch (RemoteException e) {
                onError(AccountManager.ERROR_CODE_REMOTE_EXCEPTION,
                        "remote exception");
            }
        }

这里的service，即是AbstractAuthenticator抽象类提供的IBinder:

public abstract class AbstractAccountAuthenticator {
    ...

    private class Transport extends IAccountAuthenticator.Stub {
        public void addAccount(IAccountAuthenticatorResponse response, String accountType,
                String authTokenType, String[] features, Bundle options)
                throws RemoteException {
            ...

            try {
                final Bundle result = AbstractAccountAuthenticator.this.addAccount(
                    new AccountAuthenticatorResponse(response),
                        accountType, authTokenType, features, options);
                ...
            }
            ...
        }
        ...
    }
    ...
    private Transport mTransport = new Transport();

    /**
     * @return the IBinder for the AccountAuthenticator
     */
    public final IBinder getIBinder() {
        return mTransport.asBinder();
    }
    ...
}

AbstractAccountAuthenticator的内部类Transport是IAccountAuthenticator接口的一个实现。后者规定了Authenticator的一组行为。

以添加帐号的操作为例，作为接口实现的Transport的addAccount()方法调用了AbstractAccountAuthenticator类的addAccount()抽象方法，这个方法的具体实现，则由应用程序中定义的authenticator子类来完成。

这里涉及到IPC，应用程序是服务端，提供服务的实现，而AccountManagerService则是客户端，负责通过代理对象发起调用。

Email的authenticator实现：

    class PopImapAuthenticator extends AbstractAccountAuthenticator {
        ...

        @Override
        public Bundle addAccount(AccountAuthenticatorResponse response, String accountType,
                String authTokenType, String[] requiredFeatures, Bundle options)
                throws NetworkErrorException {
            // There are two cases here:
            // 1) We are called with a username/password; this comes from the traditional email
            //    app UI; we simply create the account and return the proper bundle
            if (options != null && options.containsKey(OPTIONS_PASSWORD)
                    && options.containsKey(OPTIONS_USERNAME)) {
                final Account account = new Account(options.getString(OPTIONS_USERNAME),
                        AccountManagerTypes.TYPE_POP_IMAP);
                AccountManager.get(PopImapAuthenticatorService.this).addAccountExplicitly(
                            account, options.getString(OPTIONS_PASSWORD), null);

                ...

                Bundle b = new Bundle();
                b.putString(AccountManager.KEY_ACCOUNT_NAME, options.getString(OPTIONS_USERNAME));
                b.putString(AccountManager.KEY_ACCOUNT_TYPE, AccountManagerTypes.TYPE_POP_IMAP);
                return b;
            // 2) The other case is that we're creating a new account from an Account manager
            //    activity.  In this case, we add an intent that will be used to gather the
            //    account information...
            } else {
                Bundle b = new Bundle();
                Intent intent =
                    AccountSetupBasics.actionSetupPopImapIntent(PopImapAuthenticatorService.this);
                intent.putExtra(AccountManager.KEY_ACCOUNT_AUTHENTICATOR_RESPONSE, response);
                b.putParcelable(AccountManager.KEY_INTENT, intent);
                return b;
            }
        }

1) 如果是Email应用程序内部添加新的电子邮件帐号，此时已经取得了帐号的用户名和密码，那么直接创建对应的系统帐号，并调用AccountManager.addAccountExplicitly()将其添加到系统帐号数据库中，并返回帐号名称和类型。

2) 如果是从外部，比如系统设置中添加Email帐号，则创建指向Email应用中创建帐号对应的activity的Intent，并返回。这样，AmsTask实例在完成时会通过Handler机制调用AddAccountSettings活动提交的一个回调：

   private AccountManagerCallback<Bundle> mCallback = new AccountManagerCallback<Bundle>() {
        public void run(AccountManagerFuture<Bundle> future) {
            boolean done = true;
            try {
                Bundle bundle = future.getResult();
                //bundle.keySet();
                Intent intent = (Intent) bundle.get(AccountManager.KEY_INTENT);
                if (intent != null) {
                    done = false;
                    Bundle addAccountOptions = new Bundle();
                    addAccountOptions.putParcelable(KEY_CALLER_IDENTITY, mPendingIntent);
                    addAccountOptions.putBoolean(EXTRA_HAS_MULTIPLE_USERS,
                            Utils.hasMultipleUsers(AddAccountSettings.this));
                    intent.putExtras(addAccountOptions);
                    startActivityForResult(intent, ADD_ACCOUNT_REQUEST);
            ...
    }

这样就会启动Email创建帐号的activity，之后又会走到1)中的步骤了。