Android - Content Provider

About

A content provider is a facade between the data store (Xml, Database) and the applications.

Articles Related

Benefits

Change the underlying data source without changing the application code
Leverage standard android library. SyncAdapters, Loaders and CursorsAdapters use ContentProvider. SimpleCursorAdapter
Allow others apps to access your data source securely (because of the content provider).

Steps

get Permission to use the Content Provider
Access and perform sime data operation (query, insert, update, delete)
Display a feedback (Information ,…)

Built-In Content Provider

Built-in ContentProviders

UserDictionary
AlarmClock
Calendar Provider Guide Calendar API URI: CalendarContract;Calendars.CONTENT_URI
Contacts Provider
internal audio store: MediaStore.Audio.Media.INTERNAL_CONTENT_URI
…

Model

Content URI

The content URI, see:

content://com.example.packageName:Location:Query

where:

Scheme: content. It refers to a content provider
Authority: A unique string use to locate the content provider (generally the package name of the application)
Location: Which generally points to a database table
Query: Optional. Ex: 1234?date=201260807

Manipulation example:

// The authority
public static final String CONTENT_AUTHORITY = "com.example.packageName";
// The location
public static final String PATH_LOCATION = "location";
// The content base URI
public static final Uri BASE_CONTENT_URI = Uri.parse("content://" + CONTENT_AUTHORITY);
// The URI content with location
public static final Uri CONTENT_URI = BASE_CONTENT_URI.buildUpon().appendPath(PATH_LOCATION).build();
// Add a query path element: Use buildUpon() to obtain a builder representing an existing URI.
Uri = CONTENT_URI.buildUpon().appendPath(queryString).build();

UriMatcher

PATH matches PATH exactly
PATH/# matches PATH followed by a number
PATH/* matches PATH followed by any string
PATH/*/OTHER/# matches PATH followed by a string followed by OTHER followed by a number

reference/android/content/UriMatcher.html

Content Resolver

The content resolver locates the provider through the authority part of the content URI.

Content Resolver function mapping:

query: Read from the data
insert: Add to the data
])|update: Change preexisting data
])|delete: Delete from the data

Cursor

Android - Cursor

Code

In a onCreate activity function:

import android.content.ContentResolver;

public class MainActivity extends ActionBarActivity {

public static final String LOG_TAG = MainActivity.class.getSimpleName();

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        
        super.onCreate(savedInstanceState);
        
        // Get the TextView which will be populated with the Dictionary ContentProvider data.
        setContentView(R.layout.activity_main);
        TextView dictTextView = (TextView) findViewById(R.id.dictionary_text_view);

        // Get the ContentResolver which will send a message to the ContentProvider
        ContentResolver resolver = getContentResolver();

        // Get a Cursor containing all of the rows in the Words table
        Cursor cursor = resolver.query(UserDictionary.Words.CONTENT_URI, null, null, null, null);

        try {

            dictTextView.append("The user dictionary contains: " + cursor.getCount() + "\n");

            int idIndex = cursor.getColumnIndex(Words._ID);
            int idWord = cursor.getColumnIndex(Words.WORD);
            int idFrequency = cursor.getColumnIndex(Words.FREQUENCY);
            
            while (cursor.moveToNext()) {
               
                String wordRow = cursor.getString(idIndex) + " - " + cursor.getString(idWord) + " - " + cursor.getString(idFrequency) + "\n";
                Log.v(LOG_TAG, wordRow);
                dictTextView.append(wordRow);
                
            }

        } finally {
            cursor.close();
        }
        
    }
}

Registration

Registration of the content provider with the package manager.

See The provider element in the manifest file.

<manifest >
    <application>
         ...............
         <!-- Content Authority = Normally the package of your application -->
         <!-- Content Provider Class = Can be relative to the content authority package -->
         <!-- android:exported="true" : the provider is shared with others application -->
         <!-- android:permission. When exported="true" a license permission can be given -->
        <provider
            android:authorities="CONTENT AUTHORITY"  
            android:name="CONTENT PROVIDER CLASS" 
            android:enabled="true"
            android:exported="true" 
            android:permission="com.myapp.license"
            />
    </application>
    
    <!-- android:permission. When exported="true" a license permission can be given -->    
    <permission
        android:name="com.myapp.license"
        android:protectionlevel="dangerous"
        android:label="Licence description"
     </permission>
     
</manifest>

Example:

<manifest >
    <application>
         ...............
        <provider
            android:authorities="com.example.android.sunshine.app"
            android:name="com.example.android.sunshine.app.data.WeatherProvider"
            />
    </application>
</manifest>

Test checks to make sure that the content provider is registered correctly:

public void testProviderRegistry() {

	String providerName = WeatherProvider.class.getSimpleName();
	String providerClass = WeatherProvider.class.getName();
	String contentAuthority = WeatherContract.CONTENT_AUTHORITY;

	// Get the package manager
	PackageManager pm = mContext.getPackageManager();

	// We define the component name based on the package name from the context and the
	// WeatherProvider class.
	ComponentName componentName = new ComponentName(mContext.getPackageName(),providerClass);
	try {

		// Fetch the provider info using the component name from the PackageManager
		// This throws an exception if the provider isn't registered.
		ProviderInfo providerInfo = pm.getProviderInfo(componentName, 0);

		// Make sure that the registered authority matches the authority from the Contract.
		assertEquals("Error: "+providerName+" registered with authority: " + providerInfo.authority +
				" instead of authority: " + contentAuthority,
				providerInfo.authority, contentAuthority);

	} catch (PackageManager.NameNotFoundException e) {
		// I guess the provider isn't registered correctly.
		assertTrue("Error: "+providerName+" not registered at " + mContext.getPackageName(),
				false);
	}
}