Here, comes the elegant way of sharing your app data with other apps reliably. Content Providers!
Content provider is a wrapper over the database which allows other applications to access data generated by our app. The wrapper consists of the methods written for database's read, update & delete operations on SQLite database.
For custom content provider, we need to have the app database built up and we will be providing the wrapper over it for other applications. To make other apps aware that a content provider is available, declare it in AndroidManifest.xml as:
Here the name refers to the class MyContentProvider which extends ContentProvider class. You need to override following methods in this class.
- onCreate()
- delete(Uri, String, String[])
- getType(Uri)
- insert(Uri, ContentValues)
- query(Uri, String[], String, String[], String)
- update(Uri, ContentValues, String, String[])
public class MyContentProvider extends ContentProvider {
DatabaseHelper mDatabase;
private static final int RECORDS = 1;
public static final Uri CONTENT_URI = Uri
.parse("content://com.example.android.contentprovider");
public static final String AUTHORITY = "com.example.android.contentprovider";
private static final UriMatcher matcher = new UriMatcher(
UriMatcher.NO_MATCH);
static {
matcher.addURI(AUTHORITY, "records", RECORDS);
}
@Override
public int delete(Uri uri, String selection, String[] selectionArgs) {
// the app specific code for deleting records from database goes here
return 0;
}
@Override
public String getType(Uri uri) {
int matchType = matcher.match(uri);
switch (matchType) {
case RECORDS:
return ContentResolver.CURSOR_DIR_BASE_TYPE + "/records";
default:
throw new IllegalArgumentException("Unknown or Invalid URI " + uri);
}
}
@Override
public Uri insert(Uri uri, ContentValues values) {
//your app specific insertion code goes here
// it can be as simple as follows; inserting all values in database and returning the record id
long id = mDatabase.getWritableDatabase().insert(Helper.TABLE_NAME,
null, values);
uri = Uri.withAppendedPath(uri, "/" + id);
return uri;
}
@Override
public boolean onCreate() {
//initialize your database constructs
return true;
}
@Override
public Cursor query(Uri uri, String[] projection, String selection,
String[] selectionArgs, String sortOrder) {
//build your query with SQLiteQueryBuilder
SQLiteQueryBuilder qBuilder = new SQLiteQueryBuilder();
qBuilder.setTables(Helper.TABLE_NAME);
int uriType = matcher.match(uri);
//query the database and get result in cursor
Cursor resultCursor = qBuilder.query(mDatabase.getWritableDatabase(),
projection, selection, selectionArgs, null, null, sortOrder,
null);
resultCursor.setNotificationUri(getContext().getContentResolver(), uri);
return resultCursor;
}
@Override
public int update(Uri uri, ContentValues values, String selection,
String[] selectionArgs) {
// to be implemented
return 0;
}
}
By providing a content provider you avoid giving access to your database to other developers and also reduce the chances of database inconsistency.
