Android SQLite and ContentProvider

Table of Contents

Preface

1. Welcome

2. Prerequisites

3. How this book is organized

4. Kindle Edition

5. Errata

6. About the Author

7. Acknowledgement

1. SQLite and Android

1.1. What is SQLite

1.2. SQLite in Android

2. SQlite Overview

2.1. Packages

2.2. SQLiteOpenHelper

2.3. SQLiteDatabase

2.4. rawQuery() Example

2.5. query() Example

2.6. Cursor

2.7. ListViews, ListActivities and SimpleCursorAdapter

3. Conventions for the tutorials of this book

4. Tutorial: Using SQLite

4.1. Introduction

4.2. Create Project

4.3. Database and Data Model

4.4. User Interface

4.5. Running the apps

5. ContentProvider

5.1. Overview

5.2. Own ContentProvider

5.3. Security

5.4. Thread Safety

6. Tutorial: Using existing ContentProviders

6.1. Overview

6.2. Create contacts on your emulator

6.3. Using the Contact Content Provider

7. Loader and Activities

7.1. Activities

7.2. Loader

8. Tutorial: SQLite, own ContentProvider and Loader

8.1. Overview

8.2. Project

8.3. Database classes

8.4. Create ContentProvider

8.5. Resources

8.6. Layouts

8.7. Activities

8.8. Start your application

9. Accessing your SQLite database

9.1. Requirements

9.2. Using the shell

Android SQLite and ContentProvider

Database handling on Android

Lars Vogel

Version 4.0

Copyright © 2009, 2010, 2011, 2012 Lars Vogel

The vogella name and logo, Wizard's Wand, and related trade dress are trademarks of Lars Vogel.

All other trademarks referenced in this book are trademarks of their respective firms.

The publisher and author(s) assume no responsibility for errors or omissions or for damages resulting from the use of the information contained herein.

Portions of this book, especially the Android robot, are modifications based on work created and shared by Google and used according to terms described in the Creative Commons 3.0 Attribution License.

The title page of this book uses the Android robot graphic from http://en.wikipedia.org/wiki/File:Android_robot.svg. Please see the website for the contributing authors.

This book is also available online in a slightly different version.

17.01.2012

Preface

1. Welcome

Thank you for purchasing this book.

If you come to this book after having read other books from the Wandering Wizard Series, thank you for sticking to the series!

If you have bought to this book after having learned about SQLite and Android on my vogella.de website, thanks for getting the offline version. I hope that having this material available offline will help you work more efficiently.

I hope you enjoy your learning experience.

2. Prerequisites

This book assumes that you have prior knowledge in developing Android applications, i.e. that you know how to create Android applications via the wizard and how to work on the project resources. It also assumes that you know how to install and use the Android Development Tools for Eclipse.

The tutorials in this book can be exercised under Linux, Windows or Mac OS X. The screenshots were taken under Windows and Linux.

In case you picked this book in order to learn about basic Android programming or SQL you should start with a different reference first.

3. How this book is organized

This book demonstrates how you can develop Android applications using the integrated SQLite database. It also demonstrates how to use and create ContentProviders for accessing data. ContentProviders are Java classes which allow to share data between applications. They also provide a structured interface to access data.

The tutorials of this book have been developed and tested with Android 4.0.3, API Level 15.

The book assumes that you are already familiar with the Android Development Tools for Eclipse and with creating simple Android applications.

The first chapter gives an introduction into SQLite and its usage on Android.

The second chapter introduces the main SQLite classes and how to use them. It also gives examples how to create and run queries to your database.

The third chapter contains a tutorial in which you create a new Android project which uses SQLite to store its data. In the tutorial you will use a wrapper class (data access object) which handles the access to the database.

In the fourth chapter we have a look at ContentProviders. It explains what a ContentProvider is, how you can access existing ones and how to define your own one.

In this chapter you also learn how to define a ContentProviders that is only visible to your application and learn about thread-safety with ContentProviders.

The next chapter is a tutorial which shows how to access an existing ContentProvider. You create an Android application which accesses the data from the "People" application .

The sixth chapter explains the Loader API which was introduced in Android 3.0. Loader loads the data asynchronously. Activities should use this new API to manage their database connection (Cursor).

The seventh chapter is a tutorial in which you create an application to manage your tasks. You create your own ContentProvider for accessing the SQLite database and use the Loader API for accessing and managing the database Cursor.

Accessing the SQLite database directly on the command line is part of the eighth chapter.

4. Kindle Edition

The space on the Kindle is limited which affects the readability of example coding. I tried to create the coding as condense as possible. You still might want to switch to landscape mode for reading the coding.

5. Errata

Every book has errors to a certain degree. You can find a list of the known bugs on the errata page of the vogella.de website. The URL to this page is http://www.vogella.de/book/androidsqlite/errata.html

In case you find errors which are not yet reported please let me know under: erratavogella@gmail.com.

Errors might be one of the following:

- Typographical errors

- Examples that do not work as described in the book

- Factual errors that cannot be open to interpretation

6. About the Author

Lars Vogel is an Eclipse and Android Evangelist and maintains the website vogella.de with many Android and Eclipse related tutorials. vogella.de has more then 40 000 daily visitors.

He works as an independent Android and Eclipse consultant and trainer.

He is a regular speaker at international conferences, as for example EclipseCon, Devoxx, Droidcon, O'Reilly's Android Open and has also presented at the Google Headquarters in Mountain View.

In 2010, Lars received the "Eclipse Top Contributor Award".

7. Acknowledgement

The creation of this book did not follow the typical book creation process. It started (and still is) as a tutorial on my webpage.

I got many suggestions or corrections from countless readers of my website and I would like to express my deepest gratitude for their contributions.

Chapter 1. SQLite and Android

This chapter introduces the SQLite database and explains how SQLite relates to Android. It also mentions ContentProviders as a way to share data between applications.

1.1. What is SQLite

SQLite is an Open Source Database which is embedded into Android. SQLite supports standard relational database features like SQL syntax, transactions and prepared statements. In addition it requires only little memory at runtime (approx. 250 KByte).

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 saving them 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 available on every Android device. Using an SQLite database in Android does not require any database setup or administration.

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 filesystem. This can be slow. Therefore it is recommended to perform database operations asynchronously, for example via the AsyncTask class. .

If your application creates a database, this database is 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.

Chapter 2. SQlite Overview

In this chapter you learn about the important SQLite related Android classes. You learn about SQLiteOpenHelper and SQLiteDatabase to open and work with databases. The Cursor class will also be discussed. Cursor allows to access data from a database query.

2.1. Packages

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

2.2. SQLiteOpenHelper

To create and upgrade a database in your Android application you usually subclass SQLiteOpenHelper. 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 onCreate() and onUpgrade() methods.

onCreate() is called by the framework, if the database does not exists.

onUpgrade() is called, if the database version is increased in your application code. This method allows you to update the database schema.

Both methods receive an SQLiteDatabase object as parameter which represents the database.

SQLiteOpenHelper provides the methods getReadableDatabase() and getWriteableDatabase() 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.

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

2.3. 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 SQL 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 statement as input.

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

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

2.4. rawQuery() Example

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

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

2.5. 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 2.1. Parameters of the query() method

Parameter

Comment

String dbName

The table name to compile the query against.

int[] 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.

2.6. 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.

2.7. 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.

This tutorial will use ListActivities but not look into the details of them.

Chapter 3. Conventions for the tutorials of this book

The tutorials of this book have been developed and tested with Android 4.0.3, API Level 15.

Please use this version for all tutorials in this book.

The base package for the projects is always the same as the project name, e.g. if you are asked to create a project "de.vogella.android.sqlite.first" then the corresponding package name is "de.vogella.android.sqlite.first".

The Application name, which must be entered on the Android project generation wizard, will not be predefined. Choose a name you like.

Chapter 4. Tutorial: Using SQLite

In this chapter you create a Android application which uses a SQLite database. The application will use a data access object to access the data so that the user can focus on the main concepts of the database.

4.1. Introduction

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 withUse 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 a project de.vogella.android.sqlite.first with the "TestDatabaseActivity" Activity.

4.3. Database and Data Model

Create the MySQLiteHelper class. This class is responsible for creating the database. The onUpdate() 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);
// To show how to query
Cursor cursor = database.query(MySQLiteHelper.TABLE_COMMENTS,
allColumns, MySQLiteHelper.COLUMN_ID + " = " + insertId, null,
null, null, null);
cursor.moveToFirst();
return cursorToComment(cursor);
}

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 layout file "main.xml" in the folder "res/layout" 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="fill_parent"
android:layout_height="fill_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="fill_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.

Chapter 5. ContentProvider

This chapter explains what a ContentProvider is, how you can access existing ones and how to define your own one. It also gives pointers about security and thread-safety.

5.1. Overview

An SQLite database is private to the application which creates it. If you want to share data with other applications you can use a ContentProvider.

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

A ContentProvider can be used internally in an application to access data. If the data should be shared with another application a ContentProvider allows this.

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

Many Android datasources, e.g. the contacts, are accessible via ContentProviders. Typically the implementing classes for a ContentProviders provide public constants for the URI's.

5.2. Own ContentProvider

To create your own ContentProvider you have to define a class which extends android.content.ContentProvider. You also define your ContentProvider in the "AndroidManifest.xml" file. This entry must specify the android:authorities attribute which allows to identify the ContentProvider. 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 ContentProvider must implement several methods, e.g. query(), insert(), update(), delete(), getType() and onCreate(). In case you don't support certain methods its good practice to throw an UnsupportedOperationException().

The query() method must return a Cursor object.

5.3. Security

Per default a ContentProvider will be available to other programs. If you want to use your ContentProvider only internally you can use the attribute android:exported=false in the definition of your ContentProvider in the AndroidManifest.xml.

5.4. Thread Safety

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

The ContentProvider 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 ContentProvider, 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 ContentProvider, 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).

Chapter 6. Tutorial: Using existing ContentProviders

This chapter demonstrates how to access the data from the "People" application. The "People" app allows to store contact data.

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 menu entry "People" to create contacts.

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.

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 de.vogella.android.contentprovider with the Activity "ContactsView".

Change the layout file "main.xml" in the folder "res/layout". Rename the ID of the existing TextView to "contactview". Delete the default text. Also change the layout_height to "fill_parent".

The resulting "main.xml" 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="fill_parent"
android:layout_height="fill_parent"
android:orientation="vertical" >

<TextView
android:id="@+id/contactview"
android:layout_width="fill_parent"
android:layout_height="fill_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 "Uses Permission". From the drop-down list select the entry "android.permission.READ_CONTACTS".

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 ContactsView extends Activity {
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
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 but I wanted to keep this example simple.

Chapter 7. Loader and Activities

Loader have been introduced in Android 3.0 and are the preferred way to manage the Cursor for an Activity. This chapter introduces the concepts of a CursorLoader in conjunction with an Activity.

7.1. Activities

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.

7.2. Loader

Loaders have been introduced in Android 3.0 and are part of the compatibility layer for older Android versions (from Android 1.6). They are available in every Activity and Fragment.

Loaders allow to load data asynchronously, can monitor the source of the data and deliver new results when the content changes. They reconnect to the last Loaders Cursor after a configuration change.

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

An Activity which uses a Loader for managing a Cursor would implement the LoaderManager.LoaderCallbacks interface.

The Activity can trigger the creation of the Loader via the getLoaderManager().initLoader(0, null, this) method call.

The third parameter of initLoader() is the class which is called once the initialization has been started (callback class). Typically the Activity is used as callback class. The first parameter is a unique ID which can be used by the callback class to identify which Loader should be created. The second parameter is a bundle which can be given to the callback class for more information.

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 is created the onLoadFinished() method of the callback class is called. Here you can update your user interface. The SimpleCursorAdapter class, which can be used with ListViews, has the swapCursor() method which allows to safely use the new Cursor for the ListView.

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

Chapter 8. Tutorial: SQLite, own ContentProvider and Loader

In this chapter the user will create an SQLite database and a ContentProvider for accessing it. The Loader class will be used, for accessing and managing the Cursor.

8.1. 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.

8.2. Project

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

8.3. 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.

8.4. 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>

8.5. 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>

8.6. 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 don't 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 Development 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="fill_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="fill_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="fill_parent"
android:layout_height="fill_parent"
android:orientation="vertical" >

<ListView
android:id="@android:id/list"
android:layout_width="fill_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="fill_parent"
android:layout_height="fill_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="fill_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="fill_parent"
android:layout_height="fill_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>

8.7. 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);
startActivityForResult(i, ACTIVITY_CREATE);
}

// 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);

// Activity returns an result if called with startActivityForResult
startActivityForResult(i, ACTIVITY_EDIT);
}

// Called with the result of the other activity
// requestCode was the origin request code send to the activity
// resultCode is the return code, 0 is everything is ok
// intend can be used to get data
@Override
protected void onActivityResult(int requestCode, int resultCode,
Intent intent) {
super.onActivityResult(requestCode, resultCode, intent);
}

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.

8.8. 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.

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

Chapter 9. Accessing your SQLite database

This chapter gives an overview how you can access your database directly.

9.1. Requirements

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.

9.2. Using the shell

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 9.1. 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 .