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Android SQLite database and content provider - Tutorial

Based on Android 4.3

Lars Vogel

Version 5.0

19.08.2014

Revision History
Revision 0.1 - 4.9 22.12.2010 - 19.08.2014 Lars
Vogel
bug fixes and enhancements

Using the Android SQLite Database

This tutorial describes how to use the SQLite database in Android applications. It also demonstrates how to use existing ContentProvider and how to define new ones. It also demonstrates the usage of the Loader framework which allows to load data asynchronously.

The tutorial is based on Eclipse 4.2, Java 1.6 and Android 4.2.


Table of Contents

1. SQLite and Android
1.1. What is SQLite?
1.2. SQLite in Android
2. Prerequisites for this tutorial
3. SQLite architecture
3.1. Packages
3.2. Creating and updating database with SQLiteOpenHelper
3.3. SQLiteDatabase
3.4. rawQuery() Example
3.5. query() Example
3.6. Cursor
3.7. ListViews, ListActivities and SimpleCursorAdapter
4. Tutorial: Using SQLite
4.1. Introduction to the project
4.2. Create Project
4.3. Database and Data Model
4.4. User Interface
4.5. Running the apps
5. Content provider and sharing data
5.1. What is a content provider?
5.2. Accessing a content provider
5.3. Custom content provider
5.4. Security and content provider
5.5. Thread Safety
6. Tutorial: Using ContentProvider
6.1. Overview
6.2. Create contacts on your emulator
6.3. Using the Contact Content Provider
7. Loader
7.1. Purpose of the Loader class
7.2. Implementing a Loader
7.3. SQLite database and CursorLoader
8. Cursors and Loaders
9. Tutorial: SQLite, custom ContentProvider and Loader
9.1. Overview
9.2. Project
9.3. Database classes
9.4. Create ContentProvider
9.5. Resources
9.6. Layouts
9.7. Activities
9.8. Start your application
10. Accessing SQLite databases directly
10.1. Storage location of the SQLite database
10.2. Shell access to the database
11. More on ListViews
12. Performance
13. Get the Book
14. Support this website
14.1. Thank you
14.2. Questions and Discussion
15. Links and Literature
15.1. Source Code
15.2. Android SQLite resources
15.3. vogella Resources

Get the book Android SQLite book

1. SQLite and Android

1.1. What is SQLite?

SQLite is an Open Source database. SQLite supports standard relational database features like SQL syntax, transactions and prepared statements. The database requires limited memory at runtime (approx. 250 KByte) which makes it a good candidate from being embedded into other runtimes.

SQLite supports the data types TEXT (similar to String in Java), INTEGER (similar to long in Java) and REAL (similar to double in Java). All other types must be converted into one of these fields before getting saved in the database. SQLite itself does not validate if the types written to the columns are actually of the defined type, e.g. you can write an integer into a string column and vice versa.

More information about SQLite can be found on the SQLite website: http://www.sqlite.org.

1.2. SQLite in Android

SQLite is embedded into every Android device. Using an SQLite database in Android does not require a setup procedure or administration of the database.

You only have to define the SQL statements for creating and updating the database. Afterwards the database is automatically managed for you by the Android platform.

Access to an SQLite database involves accessing the file system. This can be slow. Therefore it is recommended to perform database operations asynchronously.

If your application creates a database, this database is by default saved in the directory DATA/data/APP_NAME/databases/FILENAME.

The parts of the above directory are constructed based on the following rules. DATA is the path which the Environment.getDataDirectory() method returns. APP_NAME is your application name. FILENAME is the name you specify in your application code for the database.

2. Prerequisites for this tutorial

The following assumes that you have already basic knowledge in Android development. Please check the Android development tutorial to learn the basics.

3. SQLite architecture

3.1. Packages

The android.database package contains all necessary classes for working with databases. The android.database.sqlite package contains the SQLite specific classes.

3.2. Creating and updating database with SQLiteOpenHelper

To create and upgrade a database in your Android application you create a subclass of the SQLiteOpenHelper class. In the constructor of your subclass you call the super() method of SQLiteOpenHelper, specifying the database name and the current database version.

In this class you need to override the following methods to create and update your database.

  • onCreate() - is called by the framework, if the database is accessed but not yet created.

  • onUpgrade() - called, if the database version is increased in your application code. This method allows you to update an existing database schema or to drop the existing database and recreate it via the onCreate() method.

Both methods receive an SQLiteDatabase object as parameter which is the Java representation of the database.

The SQLiteOpenHelper class provides the getReadableDatabase() and getWriteableDatabase() methods to get access to an SQLiteDatabase object; either in read or write mode.

The database tables should use the identifier _id for the primary key of the table. Several Android functions rely on this standard.

Tip

It is good practice to create a separate class per table. This class defines static onCreate() and onUpgrade() methods. These methods are called in the corresponding methods of SQLiteOpenHelper. This way your implementation of SQLiteOpenHelper stays readable, even if you have several tables.

3.3. SQLiteDatabase

SQLiteDatabase is the base class for working with a SQLite database in Android and provides methods to open, query, update and close the database.

More specifically SQLiteDatabase provides the insert(), update() and delete() methods.

In addition it provides the execSQL() method, which allows to execute an SQL statement directly.

The object ContentValues allows to define key/values. The key represents the table column identifier and the value represents the content for the table record in this column. ContentValues can be used for inserts and updates of database entries.

Queries can be created via the rawQuery() and query() methods or via the SQLiteQueryBuilder class .

rawQuery() directly accepts an SQL select statement as input.

query() provides a structured interface for specifying the SQL query.

SQLiteQueryBuilder is a convenience class that helps to build SQL queries.

3.4. rawQuery() Example

The following gives an example of a rawQuery() call.


Cursor cursor = getReadableDatabase().
  rawQuery("select * from todo where _id = ?", new String[] { id }); 

3.5. query() Example

The following gives an example of a query() call.


return database.query(DATABASE_TABLE, 
  new String[] { KEY_ROWID, KEY_CATEGORY, KEY_SUMMARY, KEY_DESCRIPTION }, 
  null, null, null, null, null);
 

The method query() has the following parameters.

Table 1. Parameters of the query() method

Parameter Comment
String dbName The table name to compile the query against.
String[] columnNames A list of which table columns to return. Passing "null" will return all columns.
String whereClause Where-clause, i.e. filter for the selection of data, null will select all data.
String[] selectionArgs You may include ?s in the "whereClause"". These placeholders will get replaced by the values from the selectionArgs array.
String[] groupBy A filter declaring how to group rows, null will cause the rows to not be grouped.
String[] having Filter for the groups, null means no filter.
String[] orderBy Table columns which will be used to order the data, null means no ordering.


If a condition is not required you can pass null, e.g. for the group by clause.

The "whereClause" is specified without the word "where", for example a "where" statement might look like: "_id=19 and summary=?".

If you specify placeholder values in the where clause via ?, you pass them as the selectionArgs parameter to the query.

3.6. Cursor

A query returns a Cursor object. A Cursor represents the result of a query and basically points to one row of the query result. This way Android can buffer the query results efficiently; as it does not have to load all data into memory.

To get the number of elements of the resulting query use the getCount() method.

To move between individual data rows, you can use the moveToFirst() and moveToNext() methods. The isAfterLast() method allows to check if the end of the query result has been reached.

Cursor provides typed get*() methods, e.g. getLong(columnIndex), getString(columnIndex) to access the column data for the current position of the result. The "columnIndex" is the number of the column you are accessing.

Cursor also provides the getColumnIndexOrThrow(String) method which allows to get the column index for a column name of the table.

A Cursor needs to be closed with the close() method call.

3.7. ListViews, ListActivities and SimpleCursorAdapter

ListViews are Views which allow to display a list of elements.

ListActivities are specialized activities which make the usage of ListViews easier.

To work with databases and ListViews you can use the SimpleCursorAdapter. The SimpleCursorAdapter allows to set a layout for each row of the ListViews.

You also define an array which contains the column names and another array which contains the IDs of Views which should be filled with the data.

The SimpleCursorAdapter class will map the columns to the Views based on the Cursor passed to it.

To obtain the Cursor you should use the Loader class.

4. Tutorial: Using SQLite

4.1. Introduction to the project

The following demonstrates how to work with an SQLite database. We will use a data access object (DAO) to manage the data for us. The DAO is responsible for handling the database connection and for accessing and modifying the data. It will also convert the database objects into real Java Objects, so that our user interface code does not have to deal with the persistence layer.

The resulting application will look like the following.

Using a DAO is not always the right approach. A DAO creates Java model objects; using a database directly or via a ContentProvider is typically more resource efficient as you can avoid the creation of model objects.

I still demonstrate the usage of the DAO in this example to have a relatively simple example to begin with. Use the latest version of Android 4.0. This is currently API Level 15. Otherwise I would have to introduce the Loader class, which should be used as of Android 3.0 for managing a database Cursor. And this class introduces additional complexity.

4.2. Create Project

Create the new Android project with the name de.vogella.android.sqlite.first and an activity called TestDatabaseActivity.

4.3. Database and Data Model

Create the MySQLiteHelper class. This class is responsible for creating the database. The onUpgrade() method will simply delete all existing data and re-create the table. It also defines several constants for the table name and the table columns.

package de.vogella.android.sqlite.first;

import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import android.util.Log;

public class MySQLiteHelper extends SQLiteOpenHelper {

  public static final String TABLE_COMMENTS = "comments";
  public static final String COLUMN_ID = "_id";
  public static final String COLUMN_COMMENT = "comment";

  private static final String DATABASE_NAME = "commments.db";
  private static final int DATABASE_VERSION = 1;

  // Database creation sql statement
  private static final String DATABASE_CREATE = "create table "
      + TABLE_COMMENTS + "(" + COLUMN_ID
      + " integer primary key autoincrement, " + COLUMN_COMMENT
      + " text not null);";

  public MySQLiteHelper(Context context) {
    super(context, DATABASE_NAME, null, DATABASE_VERSION);
  }

  @Override
  public void onCreate(SQLiteDatabase database) {
    database.execSQL(DATABASE_CREATE);
  }

  @Override
  public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
    Log.w(MySQLiteHelper.class.getName(),
        "Upgrading database from version " + oldVersion + " to "
            + newVersion + ", which will destroy all old data");
    db.execSQL("DROP TABLE IF EXISTS " + TABLE_COMMENTS);
    onCreate(db);
  }

} 

Create the Comment class. This class is our model and contains the data we will save in the database and show in the user interface.

package de.vogella.android.sqlite.first;

public class Comment {
  private long id;
  private String comment;

  public long getId() {
    return id;
  }

  public void setId(long id) {
    this.id = id;
  }

  public String getComment() {
    return comment;
  }

  public void setComment(String comment) {
    this.comment = comment;
  }

  // Will be used by the ArrayAdapter in the ListView
  @Override
  public String toString() {
    return comment;
  }
} 

Create the CommentsDataSource class. This class is our DAO. It maintains the database connection and supports adding new comments and fetching all comments.

package de.vogella.android.sqlite.first;

import java.util.ArrayList;
import java.util.List;

import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.SQLException;
import android.database.sqlite.SQLiteDatabase;

public class CommentsDataSource {

  // Database fields
  private SQLiteDatabase database;
  private MySQLiteHelper dbHelper;
  private String[] allColumns = { MySQLiteHelper.COLUMN_ID,
      MySQLiteHelper.COLUMN_COMMENT };

  public CommentsDataSource(Context context) {
    dbHelper = new MySQLiteHelper(context);
  }

  public void open() throws SQLException {
    database = dbHelper.getWritableDatabase();
  }

  public void close() {
    dbHelper.close();
  }

  public Comment createComment(String comment) {
    ContentValues values = new ContentValues();
    values.put(MySQLiteHelper.COLUMN_COMMENT, comment);
    long insertId = database.insert(MySQLiteHelper.TABLE_COMMENTS, null,
        values);
    Cursor cursor = database.query(MySQLiteHelper.TABLE_COMMENTS,
        allColumns, MySQLiteHelper.COLUMN_ID + " = " + insertId, null,
        null, null, null);
    cursor.moveToFirst();
    Comment newComment = cursorToComment(cursor);
    cursor.close();
    return newComment;
  }

  public void deleteComment(Comment comment) {
    long id = comment.getId();
    System.out.println("Comment deleted with id: " + id);
    database.delete(MySQLiteHelper.TABLE_COMMENTS, MySQLiteHelper.COLUMN_ID
        + " = " + id, null);
  }

  public List<Comment> getAllComments() {
    List<Comment> comments = new ArrayList<Comment>();

    Cursor cursor = database.query(MySQLiteHelper.TABLE_COMMENTS,
        allColumns, null, null, null, null, null);

    cursor.moveToFirst();
    while (!cursor.isAfterLast()) {
      Comment comment = cursorToComment(cursor);
      comments.add(comment);
      cursor.moveToNext();
    }
    // make sure to close the cursor
    cursor.close();
    return comments;
  }

  private Comment cursorToComment(Cursor cursor) {
    Comment comment = new Comment();
    comment.setId(cursor.getLong(0));
    comment.setComment(cursor.getString(1));
    return comment;
  }
} 

4.4. User Interface

Change your main.xml layout file in the res/layout folder to the following. This layout has two buttons for adding and deleting comments and a ListView which will be used to display the existing comments. The comment text will be generated later in the activity by a small random generator.

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical" >

    <LinearLayout
        android:id="@+id/group"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content" >

        <Button
            android:id="@+id/add"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="Add New" 
            android:onClick="onClick"/>

        <Button
            android:id="@+id/delete"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="Delete First" 
            android:onClick="onClick"/>
        
    </LinearLayout>

    <ListView
        android:id="@android:id/list"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="@string/hello" />

</LinearLayout> 

Change your TestDatabaseActivity class. to the following. We use here a ListActivity for displaying the data.

package de.vogella.android.sqlite.first;

import java.util.List;
import java.util.Random;

import android.app.ListActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.ArrayAdapter;

public class TestDatabaseActivity extends ListActivity {
  private CommentsDataSource datasource;

  @Override
  public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);

    datasource = new CommentsDataSource(this);
    datasource.open();

    List<Comment> values = datasource.getAllComments();

    // use the SimpleCursorAdapter to show the
    // elements in a ListView
    ArrayAdapter<Comment> adapter = new ArrayAdapter<Comment>(this,
        android.R.layout.simple_list_item_1, values);
    setListAdapter(adapter);
  }

  // Will be called via the onClick attribute
  // of the buttons in main.xml
  public void onClick(View view) {
    @SuppressWarnings("unchecked")
    ArrayAdapter<Comment> adapter = (ArrayAdapter<Comment>) getListAdapter();
    Comment comment = null;
    switch (view.getId()) {
    case R.id.add:
      String[] comments = new String[] { "Cool", "Very nice", "Hate it" };
      int nextInt = new Random().nextInt(3);
      // save the new comment to the database
      comment = datasource.createComment(comments[nextInt]);
      adapter.add(comment);
      break;
    case R.id.delete:
      if (getListAdapter().getCount() > 0) {
        comment = (Comment) getListAdapter().getItem(0);
        datasource.deleteComment(comment);
        adapter.remove(comment);
      }
      break;
    }
    adapter.notifyDataSetChanged();
  }

  @Override
  protected void onResume() {
    datasource.open();
    super.onResume();
  }

  @Override
  protected void onPause() {
    datasource.close();
    super.onPause();
  }

} 

4.5. Running the apps

Install your application and use the Add and Delete button. Restart your application to validate that the data is still there.

5. Content provider and sharing data

5.1. What is a content provider?

A SQLite database is private to the application which creates it. If you want to share data with other applications you can use a content provider (short provider).

A provider allows applications to access data. In most cases this data is stored in an SQlite database.

While a content provider can be used within an application to access data, its is typically used to share data with other application. As application data is by default private, a content provider is a convenient to share you data with other application based on a structured interface.

A content provider must be declared in the AndroidManifest.xml file.

5.2. Accessing a content provider

The access to a content provider is done via an URI. The basis for the URI is defined in the declaration of the provider in the AndroidManifest.xml file via the android:authorities attribute.

Tip

As it is required to know the URIs of a provider to access it, it is good practice to provide public constants for the URIs to document them to other developers.

Many Android datasources, e.g. the contacts, are accessible via content providers.

5.3. Custom content provider

To create your custom content provider you have to define a class which extends android.content.ContentProvider. You must declare this class as content provider in the Android manifest file. The corresponding entry must specify the android:authorities attribute which allows identifying the content provider. This authority is the basis for the URI to access data and must be unique.

<provider
       android:authorities="de.vogella.android.todos.contentprovider"
       android:name=".contentprovider.MyTodoContentProvider" >
</provider> 

Your content provider must implement several methods, e.g. query(), insert(), update(), delete(), getType() and onCreate(). In case you do not support certain methods its good practice to throw an UnsupportedOperationException().

The query() method must return a Cursor object.

5.4. Security and content provider

Until Android version 4.2 a content provider is by default available to other Android applications. As of Android 4.2 a content provider must be explicitly exported.

To set the visibility of your content provider use the android:exported=false|true parameter in the declaration of your content provider in the AndroidManifest.xml file.

Tip

It is good practice to always set the android:exported parameter to ensure correct behavior across Android versions.

5.5. Thread Safety

If you work directly with databases and have multiple writers from different threads you may run into concurrency issues.

A content provider can be accessed from several programs at the same time, therefore you must implement the access thread-safe. The easiest way is to use the keyword synchronized in front of all methods of the provider, so that only one thread can access these methods at the same time.

If you do not require that Android synchronizes data access to the provider, set the android:multiprocess=true attribute in your <provider> definition in the AndroidManifest.xml file. This permits an instance of the provider to be created in each client process, eliminating the need to perform interprocess communication (IPC).

6. Tutorial: Using ContentProvider

6.1. Overview

The following example will use an existing ContentProvider from the People application.

6.2. Create contacts on your emulator

For this example we need a few maintained contacts. Select the home menu and then the People entry to create contacts.

Selecting the "Contacts" application from the application choicer

The app will ask you if you want to login. Either login or select "Not now". Press ""Create a new contact". You can create local contacts.

Create a new contact

Details for a maintained contact

Finish adding your first contact. Afterwards the app allows you to add more contacts via the + button. As a result you should have a few new contacts in your application.

6.3. Using the Contact Content Provider

Create a new Android project called de.vogella.android.contentprovider with the activity called ContactsActivity.

Change the corresponding layout file in the res/layout folder. Rename the ID of the existing TextView to contactview. Delete the default text.

The resulting layout file should look like the following.

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical" >

    <TextView
        android:id="@+id/contactview"
        android:layout_width="match_parent"
        android:layout_height="match_parent" />

</LinearLayout> 

Access to the contact ContentProvider requires a certain permission, as not all applications should have access to the contact information. Open the AndroidManifest.xml file, and select the Permissions tab. On that tab click the Add button, and select the Uses Permission. From the drop-down list select the android.permission.READ_CONTACTS entry.

Change the coding of the activity.

package de.vogella.android.contentprovider;

import android.app.Activity;
import android.database.Cursor;
import android.net.Uri;
import android.os.Bundle;
import android.provider.ContactsContract;
import android.widget.TextView;

public class ContactsActivity extends Activity {
  
/** Called when the activity is first created. */
@Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_contacts); TextView contactView = (TextView) findViewById(R.id.contactview); Cursor cursor = getContacts(); while (cursor.moveToNext()) { String displayName = cursor.getString(cursor .getColumnIndex(ContactsContract.Data.DISPLAY_NAME)); contactView.append("Name: "); contactView.append(displayName); contactView.append("\n"); } } private Cursor getContacts() { // Run query Uri uri = ContactsContract.Contacts.CONTENT_URI; String[] projection = new String[] { ContactsContract.Contacts._ID, ContactsContract.Contacts.DISPLAY_NAME }; String selection = ContactsContract.Contacts.IN_VISIBLE_GROUP + " = '" + ("1") + "'"; String[] selectionArgs = null; String sortOrder = ContactsContract.Contacts.DISPLAY_NAME + " COLLATE LOCALIZED ASC"; return managedQuery(uri, projection, selection, selectionArgs, sortOrder); } }

If you run this application the data is read from the ContentProvider of the People application and displayed in a TextView. Typically you would display such data in a ListView.

7. Loader

7.1. Purpose of the Loader class

The Loader class allow you to load data asynchronously in an activity or fragment. They can monitor the source of the data and deliver new results when the content changes. They also persist data between configuration changes.

If the result is retrieved by the Loader after the object has been disconnected from its parent (activity or fragment), it can cache the data.

Loaders have been introduced in Android 3.0 and are part of the compatibility layer for Android versions as of 1.6.

7.2. Implementing a Loader

You can use the abstract AsyncTaskLoader class as the basis for your own Loader implementations.

The LoaderManager of an activity or fragment manages one or more Loader instances. The creation of a Loader is done via the following method call.

# start a new loader or re-connect to existing one
getLoaderManager().initLoader(0, null, this); 

The first parameter is a unique ID which can be used by the callback class to identify that Loader later. The second parameter is a bundle which can be given to the callback class for more information.

The third parameter of initLoader() is the class which is called once the initialization has been started (callback class). This class must implement the LoaderManager.LoaderCallbacks interface. It is good practice that an activity or the fragment which uses a Loader implements the LoaderManager.LoaderCallbacks interface.

The Loader is not directly created by the getLoaderManager().initLoader() method call, but must be created by the callback class in the onCreateLoader() method.

Once the Loader has finished reading data asynchronously, the onLoadFinished() method of the callback class is called. Here you can update your user interface.

7.3. SQLite database and CursorLoader

Android provides a Loader default implementation to handle SQlite database connections, the CursorLoader class.

For a ContentProvider based on an SQLite database you would typically use the CursorLoader class. This Loader performs the database query in a background thread so that the application is not blocked.

The CursorLoader class is the replacement for Activity-managed cursors which are deprecated now.

If the Cursor becomes invalid, the onLoaderReset() method is called on the callback class.

8. Cursors and Loaders

One of the challenges with accessing databases is that this access is slow. The other challenge is that the application needs to consider the life cycle of the components correctly, e.g. opening and closing the cursor if a configuration change happens.

To manage the life cycle you could use the managedQuery() method in activities prior to Android 3.0.

As of Android 3.0 this method is deprecated and you should use the Loader framework to access the ContentProvider.

The SimpleCursorAdapter class, which can be used with ListViews, has the swapCursor() method. Your Loader can use this method to update the Cursor in its onLoadFinished() method.

The CursorLoader class reconnect the Cursor after a configuration change.

9. Tutorial: SQLite, custom ContentProvider and Loader

9.1. Overview

The following demo is also available in the Android Market. To allow more users to play with the app, it has been downported to Android 2.3. If you have a barcode scanner installed on your Android phone, you can scan the following QR Code to go to the example app in the Android market. Please note that the app looks and behaves differently due to the different Android versions, e.g. you have an OptionMenu instead of the ActionBar and the theme is different.

We will create a "To-do" application which allows the user to enter tasks for himself. These items will be stored in the SQLite database and accessed via a ContentProvider.

The tasks are called "todo items" or "todos" in this tutorial.

The application consists out of two activities, one for seeing a list of all todo items and one for creating and changing a specific todo item. Both activities will communicate via Intents.

To asynchronously load and manage the Cursor the main activity will use a Loader.

The resulting application will look similar to the following.

Todo Example application OverviewActivity

Todo Example application DetailsActivity

9.2. Project

Create the project de.vogella.android.todos with the activity called TodosOverviewActivity. Create another activity called TodoDetailActivity.

9.3. Database classes

Create the package de.vogella.android.todos.database. This package will store the classes for the database handling.

As said earlier I consider having one separate class per table as best practice. Even though we have only one table in this example we will follow this practice. This way we are prepared in case our database schema grows.

Create the following class. This class also contains constants for the table name and the columns.

package de.vogella.android.todos.database;

import android.database.sqlite.SQLiteDatabase;
import android.util.Log;

public class TodoTable {

  // Database table
  public static final String TABLE_TODO = "todo";
  public static final String COLUMN_ID = "_id";
  public static final String COLUMN_CATEGORY = "category";
  public static final String COLUMN_SUMMARY = "summary";
  public static final String COLUMN_DESCRIPTION = "description";

  // Database creation SQL statement
  private static final String DATABASE_CREATE = "create table " 
      + TABLE_TODO
      + "(" 
      + COLUMN_ID + " integer primary key autoincrement, " 
      + COLUMN_CATEGORY + " text not null, " 
      + COLUMN_SUMMARY + " text not null," 
      + COLUMN_DESCRIPTION
      + " text not null" 
      + ");";

  public static void onCreate(SQLiteDatabase database) {
    database.execSQL(DATABASE_CREATE);
  }

  public static void onUpgrade(SQLiteDatabase database, int oldVersion,
      int newVersion) {
    Log.w(TodoTable.class.getName(), "Upgrading database from version "
        + oldVersion + " to " + newVersion
        + ", which will destroy all old data");
    database.execSQL("DROP TABLE IF EXISTS " + TABLE_TODO);
    onCreate(database);
  }
} 

Create the following TodoDatabaseHelper class. This class extends SQLiteOpenHelper and calls the static methods of the TodoTable helper class.


package de.vogella.android.todos.database;

import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;

public class TodoDatabaseHelper extends SQLiteOpenHelper {

  private static final String DATABASE_NAME = "todotable.db";
  private static final int DATABASE_VERSION = 1;

  public TodoDatabaseHelper(Context context) {
    super(context, DATABASE_NAME, null, DATABASE_VERSION);
  }

  // Method is called during creation of the database
  @Override
  public void onCreate(SQLiteDatabase database) {
    TodoTable.onCreate(database);
  }

  // Method is called during an upgrade of the database,
  // e.g. if you increase the database version
  @Override
  public void onUpgrade(SQLiteDatabase database, int oldVersion,
      int newVersion) {
    TodoTable.onUpgrade(database, oldVersion, newVersion);
  }
}
 

We will use a ContentProvider for accessing the database; we will not write a data access object (DAO) as we did in the previous SQlite example.

9.4. Create ContentProvider

Create the package de.vogella.android.todos.contentprovider.

Create the following MyTodoContentProvider class which extends ContentProvider.

package de.vogella.android.todos.contentprovider;

import java.util.Arrays;
import java.util.HashSet;

import android.content.ContentProvider;
import android.content.ContentResolver;
import android.content.ContentValues;
import android.content.UriMatcher;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteQueryBuilder;
import android.net.Uri;
import android.text.TextUtils;
import de.vogella.android.todos.database.TodoDatabaseHelper;
import de.vogella.android.todos.database.TodoTable;

public class MyTodoContentProvider extends ContentProvider {

  // database
  private TodoDatabaseHelper database;

  // used for the UriMacher
  private static final int TODOS = 10;
  private static final int TODO_ID = 20;

  private static final String AUTHORITY = "de.vogella.android.todos.contentprovider";

  private static final String BASE_PATH = "todos";
  public static final Uri CONTENT_URI = Uri.parse("content://" + AUTHORITY
      + "/" + BASE_PATH);

  public static final String CONTENT_TYPE = ContentResolver.CURSOR_DIR_BASE_TYPE
      + "/todos";
  public static final String CONTENT_ITEM_TYPE = ContentResolver.CURSOR_ITEM_BASE_TYPE
      + "/todo";

  private static final UriMatcher sURIMatcher = new UriMatcher(UriMatcher.NO_MATCH);
  static {
    sURIMatcher.addURI(AUTHORITY, BASE_PATH, TODOS);
    sURIMatcher.addURI(AUTHORITY, BASE_PATH + "/#", TODO_ID);
  }

  @Override
  public boolean onCreate() {
    database = new TodoDatabaseHelper(getContext());
    return false;
  }

  @Override
  public Cursor query(Uri uri, String[] projection, String selection,
      String[] selectionArgs, String sortOrder) {

    // Uisng SQLiteQueryBuilder instead of query() method
    SQLiteQueryBuilder queryBuilder = new SQLiteQueryBuilder();

    // check if the caller has requested a column which does not exists
    checkColumns(projection);

    // Set the table
    queryBuilder.setTables(TodoTable.TABLE_TODO);

    int uriType = sURIMatcher.match(uri);
    switch (uriType) {
    case TODOS:
      break;
    case TODO_ID:
      // adding the ID to the original query
      queryBuilder.appendWhere(TodoTable.COLUMN_ID + "="
          + uri.getLastPathSegment());
      break;
    default:
      throw new IllegalArgumentException("Unknown URI: " + uri);
    }

    SQLiteDatabase db = database.getWritableDatabase();
    Cursor cursor = queryBuilder.query(db, projection, selection,
        selectionArgs, null, null, sortOrder);
    // make sure that potential listeners are getting notified
    cursor.setNotificationUri(getContext().getContentResolver(), uri);

    return cursor;
  }

  @Override
  public String getType(Uri uri) {
    return null;
  }

  @Override
  public Uri insert(Uri uri, ContentValues values) {
    int uriType = sURIMatcher.match(uri);
    SQLiteDatabase sqlDB = database.getWritableDatabase();
    int rowsDeleted = 0;
    long id = 0;
    switch (uriType) {
    case TODOS:
      id = sqlDB.insert(TodoTable.TABLE_TODO, null, values);
      break;
    default:
      throw new IllegalArgumentException("Unknown URI: " + uri);
    }
    getContext().getContentResolver().notifyChange(uri, null);
    return Uri.parse(BASE_PATH + "/" + id);
  }

  @Override
  public int delete(Uri uri, String selection, String[] selectionArgs) {
    int uriType = sURIMatcher.match(uri);
    SQLiteDatabase sqlDB = database.getWritableDatabase();
    int rowsDeleted = 0;
    switch (uriType) {
    case TODOS:
      rowsDeleted = sqlDB.delete(TodoTable.TABLE_TODO, selection,
          selectionArgs);
      break;
    case TODO_ID:
      String id = uri.getLastPathSegment();
      if (TextUtils.isEmpty(selection)) {
        rowsDeleted = sqlDB.delete(TodoTable.TABLE_TODO,
            TodoTable.COLUMN_ID + "=" + id, 
            null);
      } else {
        rowsDeleted = sqlDB.delete(TodoTable.TABLE_TODO,
            TodoTable.COLUMN_ID + "=" + id 
            + " and " + selection,
            selectionArgs);
      }
      break;
    default:
      throw new IllegalArgumentException("Unknown URI: " + uri);
    }
    getContext().getContentResolver().notifyChange(uri, null);
    return rowsDeleted;
  }

  @Override
  public int update(Uri uri, ContentValues values, String selection,
      String[] selectionArgs) {

    int uriType = sURIMatcher.match(uri);
    SQLiteDatabase sqlDB = database.getWritableDatabase();
    int rowsUpdated = 0;
    switch (uriType) {
    case TODOS:
      rowsUpdated = sqlDB.update(TodoTable.TABLE_TODO, 
          values, 
          selection,
          selectionArgs);
      break;
    case TODO_ID:
      String id = uri.getLastPathSegment();
      if (TextUtils.isEmpty(selection)) {
        rowsUpdated = sqlDB.update(TodoTable.TABLE_TODO, 
            values,
            TodoTable.COLUMN_ID + "=" + id, 
            null);
      } else {
        rowsUpdated = sqlDB.update(TodoTable.TABLE_TODO, 
            values,
            TodoTable.COLUMN_ID + "=" + id 
            + " and " 
            + selection,
            selectionArgs);
      }
      break;
    default:
      throw new IllegalArgumentException("Unknown URI: " + uri);
    }
    getContext().getContentResolver().notifyChange(uri, null);
    return rowsUpdated;
  }

  private void checkColumns(String[] projection) {
    String[] available = { TodoTable.COLUMN_CATEGORY,
        TodoTable.COLUMN_SUMMARY, TodoTable.COLUMN_DESCRIPTION,
        TodoTable.COLUMN_ID };
    if (projection != null) {
      HashSet<String> requestedColumns = new HashSet<String>(Arrays.asList(projection));
      HashSet<String> availableColumns = new HashSet<String>(Arrays.asList(available));
      // check if all columns which are requested are available
      if (!availableColumns.containsAll(requestedColumns)) {
        throw new IllegalArgumentException("Unknown columns in projection");
      }
    }
  }

} 

MyTodoContentProvider implements update(), insert(), delete() and query() methods. These methods map more or less directly to the SQLiteDatabase interface.

It also has the checkColumns() method to validate that a query only requests valid columns.

Register your ContentProvider in your AndroidManifest.xml file.

<application
  <!-- Place the following after the Activity
       Definition
  -->
  <provider
      android:name=".contentprovider.MyTodoContentProvider"
      android:authorities="de.vogella.android.todos.contentprovider" >
   </provider>
</application> 

9.5. Resources

Our application requires several resources. First define a menu listmenu.xml in the folder res/menu. If you use the Android resource wizard to create the "listmenu.xml" file, the folder will be created for you; if you create the file manually you also need to create the folder manually.

This XML file will be used to define the option menu in our application. The android:showAsAction="always" attribute will ensure that this menu entry is displayed in the ActionBar of our application.

<?xml version="1.0" encoding="utf-8"?>
<menu xmlns:android="http://schemas.android.com/apk/res/android" >

    <item
        android:id="@+id/insert"
        android:showAsAction="always"
        android:title="Insert">
    </item>

</menu> 

The user will be able to select the priority for the todo items. For the priorities we create a string array. Create the following file priority.xml in the res/values folder .

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

    <string-array name="priorities">
        <item>Urgent</item>
        <item>Reminder</item>
    </string-array>

</resources> 

Define also additional strings for the application. Edit strings.xml under res/values.

<?xml version="1.0" encoding="utf-8"?>
<resources>
  <string name="hello">Hello World, Todo!</string>
  <string name="app_name">Todo</string>
  <string name="no_todos">Currently there are no Todo items maintained</string>
  <string name="menu_insert">Add Item</string>
  <string name="menu_delete">Delete Todo</string>
  <string name="todo_summary">Summary</string>
  <string name="todo_description">Delete Todo</string>
  <string name="todo_edit_summary">Summary</string>
  <string name="todo_edit_description">Description</string>
  <string name="todo_edit_confirm">Confirm</string>
</resources> 

9.6. Layouts

We will define three layouts. One will be used for the display of a row in the list, the other ones will be used by our activities.

The row layout refers to an icon called reminder. Paste an icon of type "png" called "reminder.png" into your res/drawable folders (drawable-hdpi, drawable-mdpi, drawable-ldpi)

If you do not have an icon available you can copy the icon created by the Android wizard (ic_launcher.png in the res/drawable* folders) or rename the reference in the layout file. Please note that the Android Developer Tools sometimes change the name of this generated icon , so your file might not be called "ic_launcher.png".

Alternatively you could remove the icon definition from the "todo_row.xml" layout definition file which you will create in the next step.

Create the "todo_row.xml" layout file in the folder res/layout.


<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="wrap_content" >

    <ImageView
        android:id="@+id/icon"
        android:layout_width="30dp"
        android:layout_height="24dp"
        android:layout_marginLeft="4dp"
        android:layout_marginRight="8dp"
        android:layout_marginTop="8dp"
        android:src="@drawable/reminder" >
    </ImageView>

    <TextView
        android:id="@+id/label"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_marginTop="6dp"
        android:lines="1"
        android:text="@+id/TextView01"
        android:textSize="24dp" 
        >
    </TextView>

</LinearLayout> 

Create the todo_list.xml layout file. This layout defines how the list looks like.


<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical" >

    <ListView
        android:id="@android:id/list"
        android:layout_width="match_parent"
        android:layout_height="wrap_content" >
    </ListView>

    <TextView
        android:id="@android:id/empty"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/no_todos" />

</LinearLayout> 

Create the todo_edit.xml layout file. This layout will be used to display and edit an individual todo item in the TodoDetailActivity activity.


<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical" >

    <Spinner
        android:id="@+id/category"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:entries="@array/priorities" >
    </Spinner>

    <LinearLayout
        android:id="@+id/LinearLayout01"
        android:layout_width="match_parent"
        android:layout_height="wrap_content" >

        <EditText
            android:id="@+id/todo_edit_summary"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:hint="@string/todo_edit_summary"
            android:imeOptions="actionNext" >
        </EditText>
    </LinearLayout>

    <EditText
        android:id="@+id/todo_edit_description"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_weight="1"
        android:gravity="top"
        android:hint="@string/todo_edit_description"
        android:imeOptions="actionNext" >
    </EditText>

    <Button
        android:id="@+id/todo_edit_button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/todo_edit_confirm" >
    </Button>

</LinearLayout> 

9.7. Activities

Change the coding of your activities to the following. First TodosOverviewActivity.java.

package de.vogella.android.todos;

import android.app.ListActivity;
import android.app.LoaderManager;
import android.content.CursorLoader;
import android.content.Intent;
import android.content.Loader;
import android.database.Cursor;
import android.net.Uri;
import android.os.Bundle;
import android.view.ContextMenu;
import android.view.ContextMenu.ContextMenuInfo;
import android.view.Menu;
import android.view.MenuInflater;
import android.view.MenuItem;
import android.view.View;
import android.widget.AdapterView.AdapterContextMenuInfo;
import android.widget.ListView;
import android.widget.SimpleCursorAdapter;
import de.vogella.android.todos.contentprovider.MyTodoContentProvider;
import de.vogella.android.todos.database.TodoTable;

/*
 * TodosOverviewActivity displays the existing todo items
 * in a list
 * 
 * You can create new ones via the ActionBar entry "Insert"
 * You can delete existing ones via a long press on the item
 */

public class TodosOverviewActivity extends ListActivity implements
    LoaderManager.LoaderCallbacks<Cursor> {
  private static final int ACTIVITY_CREATE = 0;
  private static final int ACTIVITY_EDIT = 1;
  private static final int DELETE_ID = Menu.FIRST + 1;
  // private Cursor cursor;
  private SimpleCursorAdapter adapter;

  
/** Called when the activity is first created. */
@Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.todo_list); this.getListView().setDividerHeight(2); fillData(); registerForContextMenu(getListView()); } // create the menu based on the XML defintion @Override public boolean onCreateOptionsMenu(Menu menu) { MenuInflater inflater = getMenuInflater(); inflater.inflate(R.menu.listmenu, menu); return true; } // Reaction to the menu selection @Override public boolean onOptionsItemSelected(MenuItem item) { switch (item.getItemId()) { case R.id.insert: createTodo(); return true; } return super.onOptionsItemSelected(item); } @Override public boolean onContextItemSelected(MenuItem item) { switch (item.getItemId()) { case DELETE_ID: AdapterContextMenuInfo info = (AdapterContextMenuInfo) item .getMenuInfo(); Uri uri = Uri.parse(MyTodoContentProvider.CONTENT_URI + "/" + info.id); getContentResolver().delete(uri, null, null); fillData(); return true; } return super.onContextItemSelected(item); } private void createTodo() { Intent i = new Intent(this, TodoDetailActivity.class); startActivity(i); } // Opens the second activity if an entry is clicked @Override protected void onListItemClick(ListView l, View v, int position, long id) { super.onListItemClick(l, v, position, id); Intent i = new Intent(this, TodoDetailActivity.class); Uri todoUri = Uri.parse(MyTodoContentProvider.CONTENT_URI + "/" + id); i.putExtra(MyTodoContentProvider.CONTENT_ITEM_TYPE, todoUri); startActivity(i); } private void fillData() { // Fields from the database (projection) // Must include the _id column for the adapter to work String[] from = new String[] { TodoTable.COLUMN_SUMMARY }; // Fields on the UI to which we map int[] to = new int[] { R.id.label }; getLoaderManager().initLoader(0, null, this); adapter = new SimpleCursorAdapter(this, R.layout.todo_row, null, from, to, 0); setListAdapter(adapter); } @Override public void onCreateContextMenu(ContextMenu menu, View v, ContextMenuInfo menuInfo) { super.onCreateContextMenu(menu, v, menuInfo); menu.add(0, DELETE_ID, 0, R.string.menu_delete); } // creates a new loader after the initLoader () call @Override public Loader<Cursor> onCreateLoader(int id, Bundle args) { String[] projection = { TodoTable.COLUMN_ID, TodoTable.COLUMN_SUMMARY }; CursorLoader cursorLoader = new CursorLoader(this, MyTodoContentProvider.CONTENT_URI, projection, null, null, null); return cursorLoader; } @Override public void onLoadFinished(Loader<Cursor> loader, Cursor data) { adapter.swapCursor(data); } @Override public void onLoaderReset(Loader<Cursor> loader) { // data is not available anymore, delete reference adapter.swapCursor(null); } }

And TodoDetailActivity.java

package de.vogella.android.todos;

import android.app.Activity;
import android.content.ContentValues;
import android.database.Cursor;
import android.net.Uri;
import android.os.Bundle;
import android.text.TextUtils;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Spinner;
import android.widget.Toast;
import de.vogella.android.todos.contentprovider.MyTodoContentProvider;
import de.vogella.android.todos.database.TodoTable;

/*
 * TodoDetailActivity allows to enter a new todo item 
 * or to change an existing
 */
public class TodoDetailActivity extends Activity {
  private Spinner mCategory;
  private EditText mTitleText;
  private EditText mBodyText;

  private Uri todoUri;

  @Override
  protected void onCreate(Bundle bundle) {
    super.onCreate(bundle);
    setContentView(R.layout.todo_edit);

    mCategory = (Spinner) findViewById(R.id.category);
    mTitleText = (EditText) findViewById(R.id.todo_edit_summary);
    mBodyText = (EditText) findViewById(R.id.todo_edit_description);
    Button confirmButton = (Button) findViewById(R.id.todo_edit_button);

    Bundle extras = getIntent().getExtras();

    // check from the saved Instance
    todoUri = (bundle == null) ? null : (Uri) bundle
        .getParcelable(MyTodoContentProvider.CONTENT_ITEM_TYPE);

    // Or passed from the other activity
    if (extras != null) {
      todoUri = extras
          .getParcelable(MyTodoContentProvider.CONTENT_ITEM_TYPE);

      fillData(todoUri);
    }

    confirmButton.setOnClickListener(new View.OnClickListener() {
      public void onClick(View view) {
        if (TextUtils.isEmpty(mTitleText.getText().toString())) {
          makeToast();
        } else {
          setResult(RESULT_OK);
          finish();
        }
      }

    });
  }

  private void fillData(Uri uri) {
    String[] projection = { TodoTable.COLUMN_SUMMARY,
        TodoTable.COLUMN_DESCRIPTION, TodoTable.COLUMN_CATEGORY };
    Cursor cursor = getContentResolver().query(uri, projection, null, null,
        null);
    if (cursor != null) {
      cursor.moveToFirst();
      String category = cursor.getString(cursor
          .getColumnIndexOrThrow(TodoTable.COLUMN_CATEGORY));

      for (int i = 0; i < mCategory.getCount(); i++) {

        String s = (String) mCategory.getItemAtPosition(i);
        if (s.equalsIgnoreCase(category)) {
          mCategory.setSelection(i);
        }
      }

      mTitleText.setText(cursor.getString(cursor
          .getColumnIndexOrThrow(TodoTable.COLUMN_SUMMARY)));
      mBodyText.setText(cursor.getString(cursor
          .getColumnIndexOrThrow(TodoTable.COLUMN_DESCRIPTION)));

      // always close the cursor
      cursor.close();
    }
  }

  protected void onSaveInstanceState(Bundle outState) {
    super.onSaveInstanceState(outState);
    saveState();
    outState.putParcelable(MyTodoContentProvider.CONTENT_ITEM_TYPE, todoUri);
  }

  @Override
  protected void onPause() {
    super.onPause();
    saveState();
  }

  private void saveState() {
    String category = (String) mCategory.getSelectedItem();
    String summary = mTitleText.getText().toString();
    String description = mBodyText.getText().toString();

    // only save if either summary or description
    // is available

    if (description.length() == 0 && summary.length() == 0) {
      return;
    }

    ContentValues values = new ContentValues();
    values.put(TodoTable.COLUMN_CATEGORY, category);
    values.put(TodoTable.COLUMN_SUMMARY, summary);
    values.put(TodoTable.COLUMN_DESCRIPTION, description);

    if (todoUri == null) {
      // New todo
      todoUri = getContentResolver().insert(MyTodoContentProvider.CONTENT_URI, values);
    } else {
      // Update todo
      getContentResolver().update(todoUri, values, null, null);
    }
  }

  private void makeToast() {
    Toast.makeText(TodoDetailActivity.this, "Please maintain a summary",
        Toast.LENGTH_LONG).show();
  }
} 

The resulting AndroidManifest.xml looks like the following.

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="de.vogella.android.todos"
    android:versionCode="1"
    android:versionName="1.0" >

    <uses-sdk android:minSdkVersion="15" />

    <application
        android:icon="@drawable/icon"
        android:label="@string/app_name" >
        <activity
            android:name=".TodosOverviewActivity"
            android:label="@string/app_name" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
        <activity
            android:name=".TodoDetailActivity"
            android:windowSoftInputMode="stateVisible|adjustResize" >
        </activity>

        <provider
            android:name=".contentprovider.MyTodoContentProvider"
            android:authorities="de.vogella.android.todos.contentprovider" >
        </provider>
    </application>

</manifest> 

Please note that android:windowSoftInputMode="stateVisible|adjustResize" is defined for the TodoDetailActivity. This makes the keyboard harmonize better with the widgets, but it is not required for this tutorial.

9.8. Start your application

Start your application. You should be able to enter a new todo item via the "Insert" button in the ActionBar.

An existing todo item can be deleted on the list via a long press.

Deleting an todo item

To change an existing todo item, touch the corresponding row. This starts the second activity.

10. Accessing SQLite databases directly

10.1. Storage location of the SQLite database

SQlite stores the whole database in a file. If you have access to this file, you can work directly with the data base. Accessing the SQlite database file only works in the emulator or on a rooted device.

A standard Android device will not grant read-access to the database file.

10.2. Shell access to the database

It is possible to access an SQLite database on the emulator or a rooted device via the command line. For this use the following command to connect to the device.

adb shell 

The command adb is located in your Android SDK installation folder in the "platform-tools" subfolder.

Afterwards you use the "cd" command to switch the database directory and use the "sqlite3" command to connect to a database. For example in my case:

# Switch to the data directory
cd /data/data
# Our application
cd de.vogella.android.todos
# Switch to the database dir
cd databases
# Check the content
ls
# Assuming that there is a todotable file
# connect to this table
sqlite3 todotable.db 

The most important commands are:

Table 2. SQlite commands

Command Description
.help List all commands and options.
.exit Exit the sqlite3 command.
.schema Show the CREATE statements which were used to create the tables of the current database.


You find the complete documentation of SQlite at http://www.sqlite.org/sqlite.html.

11. More on ListViews

Please see Android ListView Tutorial for an introduction into ListViews and ListActivities .

12. Performance

Changes in SQLite are ACID (atomic, consistent, isolated, durable). This means that every update, insert and delete operation is ACID. Unfortunately this requires some overhead in the database processing therefore you should wrap updates in the SQLite database in an transaction and commit this transaction after several operations. This can significantly improve performance.

The following code demonstrates that performance optimization.

db.beginTransaction();
try {
   for (int i= 0; i< values.lenght; i++){
     // TODO prepare ContentValues object values
     db.insert(your_table, null, values);
     // In case you do larger updates
     yieldIfContededSafely()
     }
     db.setTransactionSuccessful();     
    } finally {
      db.endTransaction();
} 

For larger data updates you should use the yieldIfContededSafely() method. SQLite locks the database during an transaction. With this call, Android checks if someone else queries the data and if finish automatically the transaction and opens a new one. This way the other process can access the data in between.

13. Get the Book

This tutorial is part of a book available in electronic form for your Kindle.

14. Support this website

This tutorial is Open Content under the CC BY-NC-SA 3.0 DE license. Source code in this tutorial is distributed under the Eclipse Public License. See the vogella License page for details on the terms of reuse.

Writing and updating these tutorials is a lot of work. If this free community service was helpful, you can support the cause by giving a tip as well as reporting typos and factual errors.

14.1. Thank you

Please consider a contribution if this article helped you.

Flattr this

14.2. Questions and Discussion

If you find errors in this tutorial, please notify me (see the top of the page). Please note that due to the high volume of feedback I receive, I cannot answer questions to your implementation. Ensure you have read the vogella FAQ as I don't respond to questions already answered there.

15. Links and Literature

15.1. Source Code

Source Code of Examples

15.3. vogella Resources

vogella Training Android and Eclipse Training from the vogella team

Android Tutorial Introduction to Android Programming

GWT Tutorial Program in Java, compile to JavaScript and HTML

Eclipse RCP Tutorial Create native applications in Java

JUnit Tutorial Test your application

Git Tutorial Put all your files in a distributed version control system