裝過Android版的Facebook、lastfm的同學是否對於這些應用的功能感到驚喜，它們可以定期更新朋友的最新資訊，將最新近況和心情短語整合入聯絡人中。這些應用全部是以Android2.0後的賬戶和同步機制為基礎的。Google的例程中給出了名為SampleSyncAdpater的例子，通過分析該例子可以學會Android中的Account驗證、同步Adapter的使用。

詳細例子程式碼可以看sdk samples中提供的原始碼，現在拿2.2中的版本來簡要說明。

首先是 class Authenticator extends AbstractAccountAuthenticator ，該類是賬戶認證類，開啟手機的Setting裡，有Account&Sync 一項，Authenticator就是實現其中的賬號功能的類。

1. // in Authenticator.java
2.     public Bundle addAccount(AccountAuthenticatorResponse response,  
3.         String accountType, String authTokenType, String[] requiredFeatures,  
4.         Bundle options) {  
5.         final Intent intent = new Intent(mContext, AuthenticatorActivity.class);  
6.         intent.putExtra(AuthenticatorActivity.PARAM_AUTHTOKEN_TYPE,  
7.             authTokenType);  
8.         intent.putExtra(AccountManager.KEY_ACCOUNT_AUTHENTICATOR_RESPONSE,  
9.             response);  
10.         final Bundle bundle = new Bundle();  
11.         bundle.putParcelable(AccountManager.KEY_INTENT, intent);  
12.         return bundle;  
13.     }  

// in Authenticator.java public Bundle addAccount(AccountAuthenticatorResponse response, String accountType, String authTokenType, String[] requiredFeatures, Bundle options) { final Intent intent = new Intent(mContext, AuthenticatorActivity.class); intent.putExtra(AuthenticatorActivity.PARAM_AUTHTOKEN_TYPE, authTokenType); intent.putExtra(AccountManager.KEY_ACCOUNT_AUTHENTICATOR_RESPONSE, response); final Bundle bundle = new Bundle(); bundle.putParcelable(AccountManager.KEY_INTENT, intent); return bundle; }

其中addAccount方法用來定義需要增加賬號時的操作，如呼叫AuthenticatorActivity來進行賬號的新增認證。

在AuthenticatorActivity.java中定義了handleLogin()，此方法由login_activity.xml中的android:onClick="handleLogin"定義與ui中的okbutton的關聯。

1. // in layout/login_activity.xml
2. <Button  
3.             android:id="@+id/ok_button"
4.             android:layout_width="wrap_content"
5.             android:layout_height="wrap_content"
6.             android:layout_gravity="center_horizontal"
7.             android:minWidth="100dip"
8.             android:text="@string/login_activity_ok_button"
9.             android:onClick="handleLogin" />  

// in layout/login_activity.xml <Button android:id="@+id/ok_button" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_gravity="center_horizontal" android:minWidth="100dip" android:text="@string/login_activity_ok_button" android:onClick="handleLogin" />

handleLogin()將ui中的使用者名稱和密碼取得，並建立一個試圖認證的執行緒，通過網路去服務端驗證。

NetworkUtilities.java中的 public static boolean authenticate(String username, String password, Handler handler, final Context context)方法展示了通過網路驗證的具體流程。得到服務端驗證結果後，在sendResult()中通過handler.post呼叫來實現 onAuthenticationResult()在AuthenticatorActivity中的執行。 onAuthenticationResult()判斷驗證通過則結束AuthenticatorActivity，否則報出使用者名稱密碼錯，讓使用者在 AuthenticatorActivity中再次嘗試驗證。

1. // AuthenticatorActivity.java中的handleLogin()方法
2.     /** 
3.      * Handles onClick event on the Submit button. Sends username/password to 
4.      * the server for authentication. 
5.      *  
6.      * @param view The Submit button for which this method is invoked 
7.      */
8.     publicvoid handleLogin(View view) {  
9.         if (mRequestNewAccount) {  
10.             mUsername = mUsernameEdit.getText().toString();  
11.         }  
12.         mPassword = mPasswordEdit.getText().toString();  
13.         if (TextUtils.isEmpty(mUsername) || TextUtils.isEmpty(mPassword)) {  
14.             mMessage.setText(getMessage());  
15.         } else {  
16.             showProgress();  
17.             // Start authenticating...
18.             mAuthThread =  
19.                 NetworkUtilities.attemptAuth(mUsername, mPassword, mHandler,  
20.                     AuthenticatorActivity.this);  
21.         }  
22.     }  

// AuthenticatorActivity.java中的handleLogin()方法 /** * Handles onClick event on the Submit button. Sends username/password to * the server for authentication. * * @param view The Submit button for which this method is invoked */ public void handleLogin(View view) { if (mRequestNewAccount) { mUsername = mUsernameEdit.getText().toString(); } mPassword = mPasswordEdit.getText().toString(); if (TextUtils.isEmpty(mUsername) || TextUtils.isEmpty(mPassword)) { mMessage.setText(getMessage()); } else { showProgress(); // Start authenticating... mAuthThread = NetworkUtilities.attemptAuth(mUsername, mPassword, mHandler, AuthenticatorActivity.this); } }

1. // NetworkUtilities中的authenticate()方法通過網路訪問具體來實現服務端的驗證，sendResult()來使呼叫結果被AuthenticatorActivity的onAuthenticationResult()呼叫。
2.     /** 
3.      * Connects to the Voiper server, authenticates the provided username and 
4.      * password. 
5.      *  
6.      * @param username The user's username 
7.      * @param password The user's password 
8.      * @param handler The hander instance from the calling UI thread. 
9.      * @param context The context of the calling Activity. 
10.      * @return boolean The boolean result indicating whether the user was 
11.      *         successfully authenticated. 
12.      */
13.     publicstaticboolean authenticate(String username, String password,  
14.         Handler handler, final Context context) {  
15.         final HttpResponse resp;  
16.         final ArrayList<NameValuePair> params = new ArrayList<NameValuePair>();  
17.         params.add(new BasicNameValuePair(PARAM_USERNAME, username));  
18.         params.add(new BasicNameValuePair(PARAM_PASSWORD, password));  
19.         HttpEntity entity = null;  
20.         try {  
21.             entity = new UrlEncodedFormEntity(params);  
22.         } catch (final UnsupportedEncodingException e) {  
23.             // this should never happen.
24.             thrownew AssertionError(e);  
25.         }  
26.         final HttpPost post = new HttpPost(AUTH_URI);  
27.         post.addHeader(entity.getContentType());  
28.         post.setEntity(entity);  
29.         maybeCreateHttpClient();  
30.         try {  
31.             resp = mHttpClient.execute(post);  
32.             if (resp.getStatusLine().getStatusCode() == HttpStatus.SC_OK) {  
33.                 if (Log.isLoggable(TAG, Log.VERBOSE)) {  
34.                     Log.v(TAG, "Successful authentication");  
35.                 }  
36.                 sendResult(true, handler, context);  
37.                 returntrue;  
38.             } else {  
39.                 if (Log.isLoggable(TAG, Log.VERBOSE)) {  
40.                     Log.v(TAG, "Error authenticating" + resp.getStatusLine());  
41.                 }  
42.                 sendResult(false, handler, context);  
43.                 returnfalse;  
44.             }  
45.         } catch (final IOException e) {  
46.             if (Log.isLoggable(TAG, Log.VERBOSE)) {  
47.                 Log.v(TAG, "IOException when getting authtoken", e);  
48.             }  
49.             sendResult(false, handler, context);  
50.             returnfalse;  
51.         } finally {  
52.             if (Log.isLoggable(TAG, Log.VERBOSE)) {  
53.                 Log.v(TAG, "getAuthtoken completing");  
54.             }  
55.         }  
56.     }  
57.     /** 
58.      * Sends the authentication response from server back to the caller main UI 
59.      * thread through its handler. 
60.      *  
61.      * @param result The boolean holding authentication result 
62.      * @param handler The main UI thread's handler instance. 
63.      * @param context The caller Activity's context. 
64.      */
65.     privatestaticvoid sendResult(final Boolean result, final Handler handler,  
66.         final Context context) {  
67.         if (handler == null || context == null) {  
68.             return;  
69.         }  
70.         handler.post(new Runnable() {  
71.             publicvoid run() {  
72.                 ((AuthenticatorActivity) context).onAuthenticationResult(result);  
73.             }  
74.         });  
75.     }  

// NetworkUtilities中的authenticate()方法通過網路訪問具體來實現服務端的驗證，sendResult()來使呼叫結果被AuthenticatorActivity的onAuthenticationResult()呼叫。 /** * Connects to the Voiper server, authenticates the provided username and * password. * * @param username The user's username * @param password The user's password * @param handler The hander instance from the calling UI thread. * @param context The context of the calling Activity. * @return boolean The boolean result indicating whether the user was * successfully authenticated. */ public static boolean authenticate(String username, String password, Handler handler, final Context context) { final HttpResponse resp; final ArrayList<NameValuePair> params = new ArrayList<NameValuePair>(); params.add(new BasicNameValuePair(PARAM_USERNAME, username)); params.add(new BasicNameValuePair(PARAM_PASSWORD, password)); HttpEntity entity = null; try { entity = new UrlEncodedFormEntity(params); } catch (final UnsupportedEncodingException e) { // this should never happen. throw new AssertionError(e); } final HttpPost post = new HttpPost(AUTH_URI); post.addHeader(entity.getContentType()); post.setEntity(entity); maybeCreateHttpClient(); try { resp = mHttpClient.execute(post); if (resp.getStatusLine().getStatusCode() == HttpStatus.SC_OK) { if (Log.isLoggable(TAG, Log.VERBOSE)) { Log.v(TAG, "Successful authentication"); } sendResult(true, handler, context); return true; } else { if (Log.isLoggable(TAG, Log.VERBOSE)) { Log.v(TAG, "Error authenticating" + resp.getStatusLine()); } sendResult(false, handler, context); return false; } } catch (final IOException e) { if (Log.isLoggable(TAG, Log.VERBOSE)) { Log.v(TAG, "IOException when getting authtoken", e); } sendResult(false, handler, context); return false; } finally { if (Log.isLoggable(TAG, Log.VERBOSE)) { Log.v(TAG, "getAuthtoken completing"); } } } /** * Sends the authentication response from server back to the caller main UI * thread through its handler. * * @param result The boolean holding authentication result * @param handler The main UI thread's handler instance. * @param context The caller Activity's context. */ private static void sendResult(final Boolean result, final Handler handler, final Context context) { if (handler == null || context == null) { return; } handler.post(new Runnable() { public void run() { ((AuthenticatorActivity) context).onAuthenticationResult(result); } }); }

1. // AuthenticatorActivity.java中的onAuthenticationResult，來根據驗證結果來選擇結束認證或重新嘗試。
2.     /** 
3.      * Called when the authentication process completes (see attemptLogin()). 
4.      */
5.     publicvoid onAuthenticationResult(boolean result) {  
6.         Log.i(TAG, "onAuthenticationResult(" + result + ")");  
7.         // Hide the progress dialog
8.         hideProgress();  
9.         if (result) {  
10.             if (!mConfirmCredentials) {  
11.                 finishLogin();  
12.             } else {  
13.                 finishConfirmCredentials(true);  
14.             }  
15.         } else {  
16.             Log.e(TAG, "onAuthenticationResult: failed to authenticate");  
17.             if (mRequestNewAccount) {  
18.                 // "Please enter a valid username/password.
19.                 mMessage  
20.                     .setText(getText(R.string.login_activity_loginfail_text_both));  
21.             } else {  
22.                 // "Please enter a valid password." (Used when the
23.                 // account is already in the database but the password
24.                 // doesn't work.)
25.                 mMessage  
26.                     .setText(getText(R.string.login_activity_loginfail_text_pwonly));  
27.             }  
28.         }  
29.     }  

// AuthenticatorActivity.java中的onAuthenticationResult，來根據驗證結果來選擇結束認證或重新嘗試。 /** * Called when the authentication process completes (see attemptLogin()). */ public void onAuthenticationResult(boolean result) { Log.i(TAG, "onAuthenticationResult(" + result + ")"); // Hide the progress dialog hideProgress(); if (result) { if (!mConfirmCredentials) { finishLogin(); } else { finishConfirmCredentials(true); } } else { Log.e(TAG, "onAuthenticationResult: failed to authenticate"); if (mRequestNewAccount) { // "Please enter a valid username/password. mMessage .setText(getText(R.string.login_activity_loginfail_text_both)); } else { // "Please enter a valid password." (Used when the // account is already in the database but the password // doesn't work.) mMessage .setText(getText(R.string.login_activity_loginfail_text_pwonly)); } } }

Account的驗證完畢後，就生成了賬號，可以開始使用同步功能了。同步的主要邏輯在public class SyncAdapter extends AbstractThreadedSyncAdapter中實現。

1. // SyncAdapter.java中的OnPerformSync方法，主要的同步邏輯
2.     @Override
3.     publicvoid onPerformSync(Account account, Bundle extras, String authority,  
4.         ContentProviderClient provider, SyncResult syncResult) {  
5.         List<User> users;  
6.         List<Status> statuses;  
7.         String authtoken = null;  
8.          try {  
9.              // use the account manager to request the credentials
10.              authtoken =  
11.                 mAccountManager.blockingGetAuthToken(account,  
12.                     Constants.AUTHTOKEN_TYPE, true/* notifyAuthFailure */);  
13.              // fetch updates from the sample service over the cloud
14.              users =  
15.                 NetworkUtilities.fetchFriendUpdates(account, authtoken,  
16.                     mLastUpdated);  
17.             // update the last synced date.
18.             mLastUpdated = new Date();  
19.             // update platform contacts.
20.             Log.d(TAG, "Calling contactManager's sync contacts");  
21.             ContactManager.syncContacts(mContext, account.name, users);  
22.             // fetch and update status messages for all the synced users.
23.             statuses = NetworkUtilities.fetchFriendStatuses(account, authtoken);  
24.             ContactManager.insertStatuses(mContext, account.name, statuses);  
25.         } catch (final AuthenticatorException e) {  
26.             syncResult.stats.numParseExceptions++;  
27.             Log.e(TAG, "AuthenticatorException", e);  
28.         } catch (final OperationCanceledException e) {  
29.             Log.e(TAG, "OperationCanceledExcetpion", e);  
30.         } catch (final IOException e) {  
31.             Log.e(TAG, "IOException", e);  
32.             syncResult.stats.numIoExceptions++;  
33.         } catch (final AuthenticationException e) {  
34.             mAccountManager.invalidateAuthToken(Constants.ACCOUNT_TYPE,  
35.                 authtoken);  
36.             syncResult.stats.numAuthExceptions++;  
37.             Log.e(TAG, "AuthenticationException", e);  
38.         } catch (final ParseException e) {  
39.             syncResult.stats.numParseExceptions++;  
40.             Log.e(TAG, "ParseException", e);  
41.         } catch (final JSONException e) {  
42.             syncResult.stats.numParseExceptions++;  
43.             Log.e(TAG, "JSONException", e);  
44.         }  
45.     }  

// SyncAdapter.java中的OnPerformSync方法，主要的同步邏輯 @Override public void onPerformSync(Account account, Bundle extras, String authority, ContentProviderClient provider, SyncResult syncResult) { List<User> users; List<Status> statuses; String authtoken = null; try { // use the account manager to request the credentials authtoken = mAccountManager.blockingGetAuthToken(account, Constants.AUTHTOKEN_TYPE, true /* notifyAuthFailure */); // fetch updates from the sample service over the cloud users = NetworkUtilities.fetchFriendUpdates(account, authtoken, mLastUpdated); // update the last synced date. mLastUpdated = new Date(); // update platform contacts. Log.d(TAG, "Calling contactManager's sync contacts"); ContactManager.syncContacts(mContext, account.name, users); // fetch and update status messages for all the synced users. statuses = NetworkUtilities.fetchFriendStatuses(account, authtoken); ContactManager.insertStatuses(mContext, account.name, statuses); } catch (final AuthenticatorException e) { syncResult.stats.numParseExceptions++; Log.e(TAG, "AuthenticatorException", e); } catch (final OperationCanceledException e) { Log.e(TAG, "OperationCanceledExcetpion", e); } catch (final IOException e) { Log.e(TAG, "IOException", e); syncResult.stats.numIoExceptions++; } catch (final AuthenticationException e) { mAccountManager.invalidateAuthToken(Constants.ACCOUNT_TYPE, authtoken); syncResult.stats.numAuthExceptions++; Log.e(TAG, "AuthenticationException", e); } catch (final ParseException e) { syncResult.stats.numParseExceptions++; Log.e(TAG, "ParseException", e); } catch (final JSONException e) { syncResult.stats.numParseExceptions++; Log.e(TAG, "JSONException", e); } }

onPerformSync中的執行流程中，使用NetworkUtilities中的fetchFriendUpdates和 fetchFriendStatuses來訪問服務端的聯絡人更新，並使用了例程中自己封裝的ContactManager來讀取、更新聯絡人資訊。

那Account和SyncAdapter及其Service和xml定義之間是如何關聯的呢？ AndroidManifest.xml中定義了AccountAuthenticator，SyncAdapter及對應的Service和xml定義的關聯。

1. <application  
2.     android:icon="@drawable/icon"
3.     android:label="@string/label">  
4.     <!-- The authenticator service -->  
5.     <service  
6.         android:name=".authenticator.AuthenticationService"
7.         android:exported="true">  
8.         <intent-filter>  
9.             <action  
10.                 android:name="android.accounts.AccountAuthenticator" />  
11.         </intent-filter>  
12.         <meta-data  
13.             android:name="android.accounts.AccountAuthenticator"
14.             android:resource="@xml/authenticator" />  
15.     </service>  
16.     <service  
17.         android:name=".syncadapter.SyncService"
18.         android:exported="true">  
19.         <intent-filter>  
20.             <action  
21.                 android:name="android.content.SyncAdapter" />  
22.         </intent-filter>  
23.         <meta-data  
24.             android:name="android.content.SyncAdapter"
25.             android:resource="@xml/syncadapter" />  
26.         <meta-data  
27.             android:name="android.provider.CONTACTS_STRUCTURE"
28.             android:resource="@xml/contacts" />  
29.     </service>  
30.     <activity  
31.         android:name=".authenticator.AuthenticatorActivity"
32.         android:label="@string/ui_activity_title"
33.         android:theme="@android:style/Theme.Dialog"
34.         android:excludeFromRecents="true"
35.         >  
36.         <!--  
37.             No intent-filter here! This activity is only ever launched by  
38.             someone who explicitly knows the class name  
39.         -->  
40.     </activity>  
41. </application>  

<application android:icon="@drawable/icon" android:label="@string/label"> <!-- The authenticator service --> <service android:name=".authenticator.AuthenticationService" android:exported="true"> <intent-filter> <action android:name="android.accounts.AccountAuthenticator" /> </intent-filter> <meta-data android:name="android.accounts.AccountAuthenticator" android:resource="@xml/authenticator" /> </service> <service android:name=".syncadapter.SyncService" android:exported="true"> <intent-filter> <action android:name="android.content.SyncAdapter" /> </intent-filter> <meta-data android:name="android.content.SyncAdapter" android:resource="@xml/syncadapter" /> <meta-data android:name="android.provider.CONTACTS_STRUCTURE" android:resource="@xml/contacts" /> </service> <activity android:name=".authenticator.AuthenticatorActivity" android:label="@string/ui_activity_title" android:theme="@android:style/Theme.Dialog" android:excludeFromRecents="true" > <!-- No intent-filter here! This activity is only ever launched by someone who explicitly knows the class name --> </activity> </application>

更詳細的程式碼細節和執行流程，可以去把SDK中的SampleSyncAdapter程式碼執行起來體會一下，不過要實現整個流程，必須搭建聯絡人的伺服器端，例程中在目錄samplesyncadapter_server中也提供了簡單的server端python程式碼，需要搭建在google app engine上。搭建過程遇到一些問題，由於對python不熟我弄了幾天才解決好搭建成功，其中遇到的一個model moudle找不到的問題需要你在model中新建一個__init__.py的空檔案，來說明是一個python模組，如果你也遇到此問題，希望對你有幫助。

以上是從別人那裡看到的一篇不錯的文章，以下是自己在原始碼開發過程中的一些總結：

在AccountManagerService.java和RegisteredServicesCache.java的generateServicesMap()方法裡會解析所有的功能清單裡配置的有關帳戶同步的 service。如果沒有解析到會將當前加入的帳戶資訊刪除。


帳戶資訊儲存在：data/system/account.db
                                data/system/sync
                                data/system/registered-services下面

涉到的service包括：

<service
            android:name=".myservices.ContactsSyncAdapterService"
            android:exported="true">
            <intent-filter>
                <action android:name="android.content.SyncAdapter" />
            </intent-filter>
            <meta-data android:name="android.content.SyncAdapter"
                       android:resource="@xml/syncadapter_contacts" />
          </service>
        
          <service
            android:name=".myservices.CalendarSyncAdapterService"
            android:exported="true">
            <intent-filter>
                <action android:name="android.content.SyncAdapter" />
            </intent-filter>
            <meta-data android:name="android.content.SyncAdapter"
                       android:resource="@xml/syncadapter_calendar" />
          </service>   
        
          <service
            android:name=".myservices.SyncManager"
            android:enabled="true"
            >
          </service>   
        
          <service
            android:name=".service.EasAuthenticatorService"
            android:exported="true"
            android:enabled="true"
            >
            <intent-filter>
                <action android:name="android.accounts.AccountAuthenticator" />
            </intent-filter>
            <meta-data
                android:name="android.accounts.AccountAuthenticator"
                android:resource="@xml/authenticator"
                />
          </service>
                  
          <service
            android:name=".myservices.EasAuthenticatorServiceAlternate"
            android:exported="true"
            >
            <intent-filter>
                <action android:name="android.accounts.AccountAuthenticator" />
            </intent-filter>
            <meta-data
                android:name="android.accounts.AccountAuthenticator"
                android:resource="@xml/authenticator_alternate"
                />
          </service>