BasicSyncAdapter.zip
The sync adapter framework assumes that your sync adapter transfers data between device storage associated with an account and server storage that requires login access. For this reason, the framework expects you to provide a component called an authenticator as part of your sync adapter. This component plugs into the Android accounts and authentication framework and provides a standard interface for handling user credentials such as login information.
Even if your app doesn't use accounts, you still need to provide an authenticator component. If you don't use accounts or server login, the information handled by the authenticator is ignored, so you can provide an authenticator component that contains stub method implementations. You also need to provide a bound {@link android.app.Service} that allows the sync adapter framework to call the authenticator's methods.
This lesson shows you how to define all the parts of a stub authenticator that you need to satisfy the requirements of the sync adapter framework. If you need to provide a real authenticator that handles user accounts, read the reference documentation for {@link android.accounts.AbstractAccountAuthenticator}.
To add a stub authenticator component to your app, create a class that extends {@link android.accounts.AbstractAccountAuthenticator}, and then stub out the required methods, either by returning {@code null} or by throwing an exception.
The following snippet shows an example of a stub authenticator class:
/*
* Implement AbstractAccountAuthenticator and stub out all
* of its methods
*/
public class Authenticator extends AbstractAccountAuthenticator {
// Simple constructor
public Authenticator(Context context) {
super(context);
}
// Editing properties is not supported
@Override
public Bundle editProperties(
AccountAuthenticatorResponse r, String s) {
throw new UnsupportedOperationException();
}
// Don't add additional accounts
@Override
public Bundle addAccount(
AccountAuthenticatorResponse r,
String s,
String s2,
String[] strings,
Bundle bundle) throws NetworkErrorException {
return null;
}
// Ignore attempts to confirm credentials
@Override
public Bundle confirmCredentials(
AccountAuthenticatorResponse r,
Account account,
Bundle bundle) throws NetworkErrorException {
return null;
}
// Getting an authentication token is not supported
@Override
public Bundle getAuthToken(
AccountAuthenticatorResponse r,
Account account,
String s,
Bundle bundle) throws NetworkErrorException {
throw new UnsupportedOperationException();
}
// Getting a label for the auth token is not supported
@Override
public String getAuthTokenLabel(String s) {
throw new UnsupportedOperationException();
}
// Updating user credentials is not supported
@Override
public Bundle updateCredentials(
AccountAuthenticatorResponse r,
Account account,
String s, Bundle bundle) throws NetworkErrorException {
throw new UnsupportedOperationException();
}
// Checking features for the account is not supported
@Override
public Bundle hasFeatures(
AccountAuthenticatorResponse r,
Account account, String[] strings) throws NetworkErrorException {
throw new UnsupportedOperationException();
}
}
In order for the sync adapter framework to access your authenticator, you must create a bound Service for it. This service provides an Android binder object that allows the framework to call your authenticator and pass data between the authenticator and the framework.
Since the framework starts this {@link android.app.Service} the first time it needs to access the authenticator, you can also use the service to instantiate the authenticator, by calling the authenticator constructor in the {@link android.app.Service#onCreate Service.onCreate()} method of the service.
The following snippet shows you how to define the bound {@link android.app.Service}:
/**
* A bound Service that instantiates the authenticator
* when started.
*/
public class AuthenticatorService extends Service {
...
// Instance field that stores the authenticator object
private Authenticator mAuthenticator;
@Override
public void onCreate() {
// Create a new authenticator object
mAuthenticator = new Authenticator(this);
}
/*
* When the system binds to this Service to make the RPC call
* return the authenticator's IBinder.
*/
@Override
public IBinder onBind(Intent intent) {
return mAuthenticator.getIBinder();
}
}
To plug your authenticator component into the sync adapter and account frameworks, you need to provide these framework with metadata that describes the component. This metadata declares the account type you've created for your sync adapter and declares user interface elements that the system displays if you want to make your account type visible to the user. Declare this metadata in a XML file stored in the {@code /res/xml/} directory in your app project. You can give any name to the file, although it's usually called {@code authenticator.xml}.
This XML file contains a single element <account-authenticator> that
has the following attributes:
android:accountType
If your server doesn't require login, you still have to provide an account type. For the value, use a domain name that you control. While the framework uses it to manage your sync adapter, the value is not sent to your server.
android:icon
android:userVisible="true" in res/xml/syncadapter.xml,
then you must provide this icon resource. It appears in the Accounts section of
the system's Settings app.
android:smallIcon
android:icon in the Accounts section of the system's Settings app,
depending on the screen size.
android:label
android:userVisible="true" in
res/xml/syncadapter.xml, then you should provide this string. It appears in the
Accounts section of the system's Settings app, next to the icon you define for the
authenticator.
The following snippet shows the XML file for the authenticator you created previously:
<?xml version="1.0" encoding="utf-8"?>
<account-authenticator
xmlns:android="http://schemas.android.com/apk/res/android"
android:accountType="example.com"
android:icon="@drawable/ic_launcher"
android:smallIcon="@drawable/ic_launcher"
android:label="@string/app_name"/>
In a previous step, you created a bound {@link android.app.Service} that links the authenticator
to the sync adapter framework. To identify this service to the system, declare it in your app
manifest by adding the following
<service>
element as a child element of
<application>:
<service
android:name="com.example.android.syncadapter.AuthenticatorService">
<intent-filter>
<action android:name="android.accounts.AccountAuthenticator"/>
</intent-filter>
<meta-data
android:name="android.accounts.AccountAuthenticator"
android:resource="@xml/authenticator" />
</service>
The
<intent-filter>
element sets up a filter that's triggered by the intent action
{@code android.accounts.AccountAuthenticator}, which sent by the system to run the
authenticator. When the filter is triggered, the system starts {@code AuthenticatorService},
the bound {@link android.app.Service} you have provided to wrap the authenticator.
The
<meta-data>
element declares the metadata for the authenticator. The
android:name
attribute links the meta-data to the authentication framework. The
android:resource
element specifies the name of the authenticator metadata file you created previously.
Besides an authenticator, a sync adapter also requires a content provider. If your app doesn't use a content provider already, go to the next lesson to learn how to create a stub content provider; otherwise, go to the lesson Creating a Sync Adapter.