Part 1 - How It Works
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There are two classes involved in a
ContentProvider – Implements an API that exposes a set of data in a standard way. The main methods are Query, Insert, Update and Delete.
ContentResolver – A static proxy that communicates with a
ContentProvider to access its data, either from within the same application or
from another application.
A content provider is normally backed by an SQLite database, but the API
means that consuming code does not need to know anything about the underlying
SQL. Queries are done via a Uri using constants to reference column names (to
reduce dependencies on the underlying data structure), and an
returned for the consuming code to iterate over.
Consuming a ContentProvider
ContentProviders expose their functionality through a Uri that is registered
in the AndroidManifest.xml of the application that
publishes the data. There is a convention where the Uri and the data columns
that are exposed should be available as constants to make it easy to bind to the
data. Android’s built-in
ContentProviders all provide convenience classes with
constants that reference the data structure in the
Android offers access to a wide range of system and user data using
Browser – bookmarks and browser history (requires permission
CallLog – recent calls made or received with the device.
Contacts – detailed information from the user’s contact list, including people, phones, photos & groups.
MediaStore – contents of the user’s device: audio (albums, artists, genres, playlists), images (including thumbnails) & video.
Settings – system-wide device settings and preferences.
UserDictionary – contents of the user-defined dictionary used for predictive text input.
Voicemail – history of voicemail messages.
The primary classes used when working with a
ContentProvider are shown here:
The purpose of each class is described below:
ContentProvider – Implement this abstract class’s methods to expose data. The API is made available to other classes and applications via the Uri attribute that is added to the class definition.
SQLiteOpenHelper – Helps implement the SQLite datastore
that is exposed by the
UriMatcher – Use
UriMatcher in your
ContentProvider implementation to help manage Uris that are used to
query the content.
ContentResolver – Consuming code uses a
ContentProvider instance. The two classes together take care of the
inter-process communication issues, allowing data to be easily shared between
applications. Consuming code never creates a
ContentProvider class explicity;
instead, the data is accessed by creating a cursor based on a Uri exposed by the
CursorAdapter – Use
SimpleCursorAdapter to display data accessed via a
ContentProvider API allows consumers to perform a variety of operations
on the data, such as:
- Query data to return lists or individual records.
- Modify individual records.
- Add new records.
- Delete records.
This document contains an example that uses a system-provided
as well as a simple read-only example that implements a custom