账户拉活

手机系统设置里会有“帐户”一项功能，任何第三方APP都可以通过此功能将数据在一定时间内同步到服务器中去。系统在将APP帐户同步时，会将未启动的APP进程拉活。
https://github.com/googlesamples/android-BasicSyncAdapter google关于账户拉活的相关demo
首先，我们要有一个账户服务

public class AuthenticationService extends Service {

    private AccountAuthenticator accountAuthenticator;

    @Nullable
    @Override
    public IBinder onBind(Intent intent) {
        return accountAuthenticator.getIBinder();
    }

    @Override
    public void onCreate() {
        super.onCreate();
        accountAuthenticator = new AccountAuthenticator(this);
    }


    static class AccountAuthenticator extends AbstractAccountAuthenticator {


        public AccountAuthenticator(Context context) {
            super(context);
        }

        @Override
        public Bundle editProperties(AccountAuthenticatorResponse response, String accountType) {
            return null;
        }

        @Override
        public Bundle addAccount(AccountAuthenticatorResponse response, String accountType,
                                 String authTokenType, String[] requiredFeatures, Bundle options)
                throws NetworkErrorException {
            return null;
        }

        @Override
        public Bundle confirmCredentials(AccountAuthenticatorResponse response, Account account,
                                         Bundle options) throws NetworkErrorException {
            return null;
        }

        @Override
        public Bundle getAuthToken(AccountAuthenticatorResponse response, Account account, String
                authTokenType, Bundle options) throws NetworkErrorException {
            return null;
        }

        @Override
        public String getAuthTokenLabel(String authTokenType) {
            return null;
        }

        @Override
        public Bundle updateCredentials(AccountAuthenticatorResponse response, Account account,
                                        String authTokenType, Bundle options) throws
                NetworkErrorException {
            return null;
        }

        @Override
        public Bundle hasFeatures(AccountAuthenticatorResponse response, Account account,
                                  String[] features) throws NetworkErrorException {
            return null;
        }
    }
}

该服务由系统启动，不需要手动去bind，同时，我们还需要到清单文件中去注册该服务

<!--账户服务-->
<service android:name=".account.AuthenticationService">
    <intent-filter>
        <action android:name="android.accounts.AccountAuthenticator" />
    </intent-filter>
    <meta-data
        android:name="android.accounts.AccountAuthenticator"
        android:resource="@xml/accountauthenticator" />
</service>

注意上述的action必须为“android.accounts.AccountAuthenticator”，否则系统无法启动该服务，
另外我们的meta-data中需要制定一个resource

<?xml version="1.0" encoding="utf-8"?>
<account-authenticator xmlns:android="http://schemas.android.com/apk/res/android"
    android:accountType="com.dongnao.daemon.account"
    android:icon="@mipmap/ic_launcher"
    android:label="@string/app_name" />

上述的icon代表在手机账户下显示的图标。label为手机账户下显示的名称
接下来我们允许一下我们的app，然后打开设计设置页里面的账户，便能看到如图这代表我们的app已经拥有了账号服务，拥有了账号服务之后，我们再来试图往里面添加一个账号试试

public class AccountHelper {

    private static final String TAG = "AccountHelper";

    public static final String ACCOUNT_TYPE = "com.dongnao.daemon.account";

    public static void addAccount(Context context) {
        AccountManager am = (AccountManager) context.getSystemService(Context.ACCOUNT_SERVICE);
        //获得此类型的账户
        Account[] accounts = am.getAccountsByType(ACCOUNT_TYPE);
        if (accounts.length > 0) {
            Log.e(TAG, "账户已存在");
            return;
        }
        //给这个账户类型添加一个账户
        Account dongnao = new Account("dongnao", ACCOUNT_TYPE);
        am.addAccountExplicitly(dongnao, "dn", new Bundle());
    }

    /**
     * 设置 账户自动同步
     */
    public static void autoSync() {
        Account dongnao = new Account("dongnao", ACCOUNT_TYPE);
        //设置同步
        ContentResolver.setIsSyncable(dongnao, "com.dongnao.daemon.provider", 1);
        //自动同步
        ContentResolver.setSyncAutomatically(dongnao, "com.dongnao.daemon.provider", true);
        //设置同步周期
        ContentResolver.addPeriodicSync(dongnao, "com.dongnao.daemon.provider", new Bundle(), 1);

    }

}

通过addAccount，我们向系统中添加一个账户，增加后的效果为当然，上述向系统添加账户的方式需要获取相应的权限

<uses-permission android:name="android.permission.GET_ACCOUNTS"/>
<uses-permission android:name="android.permission.AUTHENTICATE_ACCOUNTS"/>

添加完账户之后，我们需要来进行账户同步，这个时候我们还需要创建一个service来进行账户同步

public class SyncService extends Service {
    SyncAdapter syncAdapter;

    private static final String TAG = "SyncService";

    @Nullable
    @Override
    public IBinder onBind(Intent intent) {
        return syncAdapter.getSyncAdapterBinder();
    }

    @Override
    public void onCreate() {
        super.onCreate();
        syncAdapter = new SyncAdapter(getApplicationContext(), true);
    }

    static class SyncAdapter extends AbstractThreadedSyncAdapter {

        public SyncAdapter(Context context, boolean autoInitialize) {
            super(context, autoInitialize);
        }

        @Override
        public void onPerformSync(Account account, Bundle extras, String authority,
                                  ContentProviderClient provider, SyncResult syncResult) {
            Log.e(TAG,"同步账户");
            //与互联网 或者 本地数据库同步账户
        }
    }
}

该service同样有系统调用，系统在执行账户同步到时候会获取ibinder，而同步数据则在onPerformSync中执行，在onPerformSync当中我们可与编写同步代码，当然，我们本节内容主要是为了
让系统拉活app，所以可以不需要编写同步代码；
我们还需要在AndroidManifest中注册该service

<service android:name=".account.SyncService">
    <intent-filter>
        <action android:name="android.content.SyncAdapter" />
    </intent-filter>
    <meta-data
        android:name="android.content.SyncAdapter"
        android:resource="@xml/sync_adapter" />
</service>
<provider
    android:name=".account.SyncProvider"
    android:authorities="com.dongnao.daemon.provider" />

action必须为”android.content.SyncAdapter“，否则系统无法启动服务，另外也必须声明resource

<?xml version="1.0" encoding="utf-8"?>
<sync-adapter xmlns:android="http://schemas.android.com/apk/res/android"
    android:accountType="com.dongnao.daemon.account"
    android:contentAuthority="com.dongnao.daemon.provider"
    android:allowParallelSyncs="false"
    android:isAlwaysSyncable="true"
    android:userVisible="false"/>
<!--contentAuthority 系统在进行账户同步的时候会查找 此auth的ContentProvider-->
<!-- allowParallelSyncs 允许多个同步-->

public class SyncProvider extends ContentProvider {
    @Override
    public boolean onCreate() {
        return false;
    }

    @Nullable
    @Override
    public Cursor query(@NonNull Uri uri, @Nullable String[] projection, @Nullable String
            selection, @Nullable String[] selectionArgs, @Nullable String sortOrder) {
        return null;
    }

    @Nullable
    @Override
    public String getType(@NonNull Uri uri) {
        return null;
    }

    @Nullable
    @Override
    public Uri insert(@NonNull Uri uri, @Nullable ContentValues values) {
        return null;
    }

    @Override
    public int delete(@NonNull Uri uri, @Nullable String selection, @Nullable String[]
            selectionArgs) {
        return 0;
    }

    @Override
    public int update(@NonNull Uri uri, @Nullable ContentValues values, @Nullable String selection, @Nullable String[] selectionArgs) {
        return 0;
    }
}

我们接下来再设置一下同步周期并设置自动同步

/**
 * 设置 账户自动同步
 */
public static void autoSync() {
    Account dongnao = new Account("dongnao", ACCOUNT_TYPE);
    //设置同步
    ContentResolver.setIsSyncable(dongnao, "com.dongnao.daemon.provider", 1);
    //自动同步
    ContentResolver.setSyncAutomatically(dongnao, "com.dongnao.daemon.provider", true);
    //设置同步周期
    ContentResolver.addPeriodicSync(dongnao, "com.dongnao.daemon.provider", new Bundle(), 1);
}

通过系统的账户同步功能来进行拉活算是一种比较可靠的方式，但是缺点就是拉活周期无法把控，不知道过多久拉活一次