Blazin: Using Content Provider in Android

In Android security model, one application cannot directly access (read/write) other application's data. Every application has its own id data directory and own protected memory area.
Content provider is the best way to share data across applications. Content provider is a set of data wrapped up in a custom API to read and write. Applications/Processes have to register themselves as a provider of data. Other applications can request Android to read/write that data through a fixed API.
Content provider API adheres to CRUD principle.


Examples for content provider are Contacts-that exposes user information to other applications, Media store-Allows other applications to access,store media files.

Content providers are simple interfaces which uses standard insert(), query(), update(), delete() methods to access application data. So it is easy to implement a content provider.

A special URI starting with content:// will be assigned to each content providers and that will be recognized across applications.

Writing a content provider:
The ContentProvider class is the central component of a content provider. To create a content provider we have to
1. Create sub class for ContentProvider.
2. Define content URI
3. Implement all the unimplemented methods. insert(), update(), query(), delete(), getType().
4. Declare the content provider in AndroidManifest.xml

Defining URI:
Content provider URI consists of four parts.
content://authority/path/id
content:// All the content provider URIs should start with this value
'authority' is Java namespace of the content provider implementation. (fully qualified Java package name)
'path' is the virtual directory within the provider that identifies the kind of data being requested.
'id' is optional part that specifies the primary key of a record being requested. We can omit this part to request all records.

Adding new records:
We need to override insert() method of the ContentProvider to insert new record to the database via content provider. The caller method will have to specify the content provider URI and the values to be inserted without the ID. Successful insert operation will return the URI value with the newly inserted ID.
For example: If we insert a new record to the content provider content://com.example/sample
the insert method will return content://com.example/sample/1

Updating records:
To update one or more records via content provider we need to specify the content provider URI. update() method of the ContentProvider is used to update records. We have to specify the ID of the record to update a single record. To update multiple records, we have to specify 'selection' parameter to indicate which rows are to be changed.
This method will return the number of rows updated.

Deleting records:
Deleting one or more records is similar to update process. We need to specify either ID or 'selection' to delete records. delete() method of the ContentProvider will return the number of records deleted.

Querying the content provider:
To query the data via content provider we orverride query() method of ContentProvider. This method has many parameters.  We can specify list columns to put into the result cursor using 'projection' parameter. We can specify 'selection' criteria. We can specify 'sortOrder' too.
If we do not specify projection, all the columns will be included in the result cursor. If we do not specify sortOrder the provider will choose its own sort order.

getType() method:
This method is used handle requests for the MIME type of the data at the given URI. We use either vnd.android.cursor.item or vnd.android.cursor.dir/
vnd.android.cursor.item is used to represent specific item. Another one is used to specify all items.

Registering the provider in AndroidManifest.xml
As with any other major parts of Android application, we have to register the content providers too in the AndroidManifest.xml.  element is used to register the content providers. is its parent element.

Here authorities is the URI authority to access the content provider. Typically this will be the fully qualified name of the content provider class.

1. Application 'MyProvider'

This application will create a content provider and share its data. This uses SQLite database 'mydb'. It has a table called 'names'. The table names have two columns id,name.

The URI of this content provider is content://com.androidBlazin.contentproviderexample.MyProvider/cte

We have layout to insert new records to the database table.

Layout xml file:

Content provider class: MyProvider.java

package com.androidblazin.contentproviderexample;

import java.util.HashMap;

import android.content.ContentProvider;
import android.content.ContentUris;
import android.content.ContentValues;
import android.content.Context;
import android.content.UriMatcher;
import android.database.Cursor;
import android.database.SQLException;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import android.database.sqlite.SQLiteQueryBuilder;
import android.net.Uri;

public class MyProvider extends ContentProvider {
 static final String PROVIDER_NAME = "com.example.contentproviderexample.MyProvider";
 static final String URL = "content://" + PROVIDER_NAME + "/cte";
 static final Uri CONTENT_URI = Uri.parse(URL);

 static final String id = "id";
 static final String name = "name";
 static final int uriCode = 1;
 static final UriMatcher uriMatcher;
 private static HashMap values;
 static {
  uriMatcher = new UriMatcher(UriMatcher.NO_MATCH);
  uriMatcher.addURI(PROVIDER_NAME, "cte", uriCode);
  uriMatcher.addURI(PROVIDER_NAME, "cte/*", uriCode);
 }

 @Override
 public int delete(Uri uri, String selection, String[] selectionArgs) {
  int count = 0;
  switch (uriMatcher.match(uri)) {
  case uriCode:
   count = db.delete(TABLE_NAME, selection, selectionArgs);
   break;
  default:
   throw new IllegalArgumentException("Unknown URI " + uri);
  }
  getContext().getContentResolver().notifyChange(uri, null);
  return count;
 }

 @Override
 public String getType(Uri uri) {
  switch (uriMatcher.match(uri)) {
  case uriCode:
   return "vnd.android.cursor.dir/cte";

  default:
   throw new IllegalArgumentException("Unsupported URI: " + uri);
  }
 }

 @Override
 public Uri insert(Uri uri, ContentValues values) {
  long rowID = db.insert(TABLE_NAME, "", values);
  if (rowID > 0) {
   Uri _uri = ContentUris.withAppendedId(CONTENT_URI, rowID);
   getContext().getContentResolver().notifyChange(_uri, null);
   return _uri;
  }
  throw new SQLException("Failed to add a record into " + uri);
 }

 @Override
 public boolean onCreate() {
  Context context = getContext();
  DatabaseHelper dbHelper = new DatabaseHelper(context);
  db = dbHelper.getWritableDatabase();
  if (db != null) {
   return true;
  }
  return false;
 }

 @Override
 public Cursor query(Uri uri, String[] projection, String selection,
   String[] selectionArgs, String sortOrder) {
  SQLiteQueryBuilder qb = new SQLiteQueryBuilder();
  qb.setTables(TABLE_NAME);

  switch (uriMatcher.match(uri)) {
  case uriCode:
   qb.setProjectionMap(values);
   break;
  default:
   throw new IllegalArgumentException("Unknown URI " + uri);
  }
  if (sortOrder == null || sortOrder == "") {
   sortOrder = name;
  }
  Cursor c = qb.query(db, projection, selection, selectionArgs, null,
    null, sortOrder);
  c.setNotificationUri(getContext().getContentResolver(), uri);
  return c;
 }

 @Override
 public int update(Uri uri, ContentValues values, String selection,
   String[] selectionArgs) {
  int count = 0;
  switch (uriMatcher.match(uri)) {
  case uriCode:
   count = db.update(TABLE_NAME, values, selection, selectionArgs);
   break;
  default:
   throw new IllegalArgumentException("Unknown URI " + uri);
  }
  getContext().getContentResolver().notifyChange(uri, null);
  return count;
 }

 private SQLiteDatabase db;
 static final String DATABASE_NAME = "mydb";
 static final String TABLE_NAME = "names";
 static final int DATABASE_VERSION = 1;
 static final String CREATE_DB_TABLE = " CREATE TABLE " + TABLE_NAME
   + " (id INTEGER PRIMARY KEY AUTOINCREMENT, "
   + " name TEXT NOT NULL);";

 private static class DatabaseHelper extends SQLiteOpenHelper {
  DatabaseHelper(Context context) {
   super(context, DATABASE_NAME, null, DATABASE_VERSION);
  }

  @Override
  public void onCreate(SQLiteDatabase db) {
   db.execSQL(CREATE_DB_TABLE);
  }

  @Override
  public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
   db.execSQL("DROP TABLE IF EXISTS " + TABLE_NAME);
   onCreate(db);
  }
 }
}

Activity calss: MainActivity.java

package com.androidblazin.contentproviderexample;

import android.app.Activity;
import android.content.ContentValues;
import android.net.Uri;
import android.os.Bundle;
import android.view.Menu;
import android.view.View;
import android.widget.EditText;
import android.widget.Toast;

public class MainActivity extends Activity {

 @Override
 protected void onCreate(Bundle savedInstanceState) {
  super.onCreate(savedInstanceState);
  setContentView(R.layout.activity_main);
 }

 @Override
 public boolean onCreateOptionsMenu(Menu menu) {
  // Inflate the menu; this adds items to the action bar if it is present.
  getMenuInflater().inflate(R.menu.activity_main, menu);
  return true;
 }

 public void onClickAddName(View view) {
  ContentValues values = new ContentValues();
  values.put(MyProvider.name, ((EditText) findViewById(R.id.txtName))
    .getText().toString());
  Uri uri = getContentResolver().insert(MyProvider.CONTENT_URI, values);
  Toast.makeText(getBaseContext(), "New record inserted", Toast.LENGTH_LONG)
    .show();
 }
}

Manifest.xml

?xml version="1.0" encoding="utf-8"?>