android账号与同步之同步实现

时间:2024-04-18 16:05:49

上一篇博文我先介绍了账号与同步的账号管理,这篇就介绍一下还有一部分。就是android给提供的sync同步机制的使用。

事实上sync机制的使用和上一篇博文中介绍的账号管理非常类似,也是基于binder机制的跨进程通信。首先它须要一个Service。这个服务提供一个Action给系统以便系统能找到它。然后就是继承和实现AbstractThreadedSyncAdapter。此类中包括实现了ISyncAdapter.Stub内部类。这个内部类封装了远程接口调用,这个类getSyncAdapterBinder()方法,返回内部类的IBinder形式,以便对AbstractThreadedSyncAdapte进行远程调用;在manifest中须要对Service注冊,并且指定meta-data。这个meta-data是一个xml文件,在SampleSyncAdapter实例中,它的名字是syncadapter.xml,这个文件指定了账号和被监听的contentprovider。

以下分别介绍这几个文件:

SyncService.java

SyncService是一个继承普通Service的服务,用来给远端进程提供服务,在onBind方法中返回IBinder。

public class SyncService extends Service {

private static final Object sSyncAdapterLock = new Object();

private static SyncAdapter sSyncAdapter = null;

@Override

    public void onCreate() {

        synchronized (sSyncAdapterLock) {

            if (sSyncAdapter == null) {

                sSyncAdapter = new SyncAdapter(getApplicationContext(), true);

            }

        }

    }

@Override

    public IBinder onBind(Intent intent) {

        return sSyncAdapter.getSyncAdapterBinder();

    }

}

它的action取值为android.content.SyncAdapter。注冊例如以下:

 <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" />

</service>

一个适配器仅仅能同步一个Authority,若想使一个账户同步多个Authority,能够向系统注冊多个绑定同一账户的sync-adapter。

syncadapter.xml

syncadapter.xml文件指定了此Service所监听的contentprovider的Authority,还指定了监听此Authority的账号类型accountType,这个账号类型和上一篇文章中的账号类型是相关的。

<sync-adapter xmlns:android="http://schemas.android.com/apk/res/android"

    android:contentAuthority="com.android.contacts"

    android:accountType="com.example.android.samplesync"

    android:supportsUploading="false"

    android:userVisible="true"

/>

android:contentAuthority 指定要同步的ContentProvider在其AndroidManifest.xml文件里有个android:authorities属性。

android:accountType 表示进行同步的账号的类型。

attributes indicate which content authority and for which account types this sync adapter serves.

android:userVisible 设置是否在“设置”中显示

defaults to true and controls whether or not this sync adapter shows up in the Sync Settings screen.

android:supportsUploading 设置是否必须notifyChange通知才干同步

defaults to true and if true an upload-only sync will be requested for all syncadapters associated with an authority whenever that authority's content provider does a notifyChange(android.net.Uri, android.database.ContentObserver, boolean) with syncToNetwork
set to true.

android:allowParallelSyncs 是否支持多账号同一时候同步

defaults to false and if true indicates that the sync adapter can handle syncs for multiple accounts at the same time. Otherwise the SyncManager will wait until the sync adapter is not in use before requesting that it sync an account's data.

android:isAlwaysSyncable 设置全部账号的isSyncable为1

defaults to false and if true tells the SyncManager to intialize the isSyncable state to 1 for that sync adapter for each account that is added.

android:syncAdapterSettingsAction 指定一个能够设置同步的activity的Action。

defaults to null and if supplied it specifies an Intent action of an activity that can be used to adjust the sync adapter's sync settings. The activity must live in the same package as the sync adapter.

SyncAdapter.java

SyncAdapter是继承自抽象类AbstractThreadedSyncAdapter的。它实现了AbstractThreadedSyncAdapter中的方法,例如以下:

@Override

    public void onPerformSync(Account account, Bundle extras, String authority,

        ContentProviderClient provider, SyncResult syncResult) {

//TODO 进行同步操作

    }

AbstractThreadedSyncAdapter内部提供startSync()和cancelSync()两个方法。两个方法主要是被远端系统进程调用。

startSync()将会启动一个线程,通过在该线程中调用

AbstractThreadedSyncAdapter的 onPerformSync(Account, Bundle, String, ContentProviderClient, SyncResult) 方法来运行同步操作。所以上面onPerformSync方法中的操作都

是在新线程中运行的。cancelSync()将会中断同步操作。