Android SQLite Database and ContentProvider - Tutorial
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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 3.7, Java 1.6 and Android 4.0.
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. 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. ContentProvider and sharing data
- 5.1. ContentProvider Overview
- 5.2. Own ContentProvider
- 5.3. Security and ContentProvider
- 5.4. Thread Safety
- 6. Tutorial: Using ContentProvider
- 6.1. Overview
- 6.2. Create contacts on your emulator
- 6.3. Using the Contact Content Provider
- 7. Activities, Loader and ContentProvider
- 7.1. Activities and Databases
- 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 SQLite databases directly
- 9.1. Storage location of the SQLite database
- 9.2. Shell access to the database
- 10. More on ListViews
- 11. Get the Kindle edition
- 12. Questions and Discussion
- 13. Links and Literature
- 13.1. Source Code
- 13.2. Android SQLite resources
- 13.3. Android Resources
- 13.4. vogella Resources
1. SQLite and Android
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 theAsyncTask
class. .
If your application creates a database, this database is saved in the directoryDATA/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 theAndroid development tutorial to learn the basics.
3. SQLite Architecture
3.1. Packages
The package android.database
contains all general classes for working with databases.android.database.sqlite
contains the SQLite specific classes.
3.2. SQLiteOpenHelper
To create and upgrade a database in your Android application you usually subclassSQLiteOpenHelper
. In the constructor of your subclass you call thesuper()
method of SQLiteOpenHelper
, specifying the database name and the current database version.
In this class you need to override the onCreate()
andonUpgrade()
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 anSQLiteDatabase
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 staticonCreate()
and onUpdate()
methods. These methods are called in the corresponding methods ofSQLiteOpenHelper
. This way your implementation of SQLiteOpenHelper
will stay 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 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.
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
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()
andmoveToNext()
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.
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 theSimpleCursorAdapter
. The SimpleCursorAdapter
allows to set a layout for each row of theListViews
.
You also define an array which contains the column names and another array which contains the IDs ofViews
which should be filled with the data.
The SimpleCursorAdapter
class will map the columns to theViews
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.
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 aContentProvider
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 theLoader
class, which should be used as of Android 3.0 for managing a databaseCursor
. And this class introduces additional complexity.
4.2. Create Project
Create the new Android project with the name de.vogella.android.sqlite.first
and anActivity
called TestDatabaseActivity.
4.3. Database and Data Model
Create the MySQLiteHelper
class. This class is responsible for creating the database. TheonUpdate()
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 statementprivate 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);}@Overridepublic void onCreate(SQLiteDatabase database) {database.execSQL(DATABASE_CREATE);}@Overridepublic 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@Overridepublic 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 fieldsprivate 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 cursorcursor.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 aListView
which will be used to display the existing comments. The comment text will be generated later in theActivity
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;@Overridepublic 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 ListViewArrayAdapter<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.xmlpublic 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 databasecomment = 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();}@Overrideprotected void onResume() {datasource.open();super.onResume();}@Overrideprotected void onPause() {datasource.close();super.onPause();}}
4.5. Running the apps
Install your application and use the
and button. Restart your application to validate that the data is still there.5. ContentProvider and sharing data
5.1. ContentProvider Overview
An SQLite database is private to the application which creates it. If you want to share data with other applications you can use aContentProvider
.
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 aContentProvider
allows this.
The access to a ContentProvider
is done via an URI. The basis for the URI is defined in the declaration of theContentProvider
in the AndroidManifest.xml
file via theandroid: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 URIs.
5.2. Own ContentProvider
To create your own ContentProvider
you have to define a class which extendsandroid.content.ContentProvider
. You also define your ContentProvider
in the AndroidManifest.xml
file. This entry must specify theandroid:authorities
attribute which allows to identify theContentProvider
. 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 do not support certain methods its good practice to throw anUnsupportedOperationException()
.
The query() method must return a Cursor object.
5.3. Security and ContentProvider
By default a ContentProvider
will be available to other programs. If you want to use yourContentProvider
only internally you can use the attributeandroid: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 keywordsynchronized
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 theAndroidManifest.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 thePeople application.
6.2. Create contacts on your emulator
For this example we need a few maintained contacts. Select the home menu and then thePeople entry 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 theActivity
called ContactsView.
Change the main.xml
layout file in the res/layout
folder. 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 theAndroidManifest.xml
file, and select the "Permissions" tab. On that tab click the 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. */@Overridepublic 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 queryUri 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 aTextView
. Typically you would display such data in a ListView
but I wanted to keep this example simple.
7. Activities, Loader and ContentProvider
7.1. Activities and Databases
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 inActivities 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 everyActivity
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 lastLoaders
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 aCursor
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 theActivity
is used as callback class. The first parameter is a unique ID which can be used by the callback class to identify whichLoader
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 theonCreateLoader()
method.
Once the Loader
is created the onLoadFinished()
method of the callback class is called. Here you can update your user interface. TheSimpleCursorAdapter
class, which can be used with ListViews
, has the swapCursor()
method which allows to safely use the newCursor
for the ListView
.
If the Cursor
becomes invalid, the onLoaderReset()
method is called on the callback class.
8. Tutorial: SQLite, own ContentProvider and Loader
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 anOptionMenu
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 aContentProvider
.
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. BothActivities will communicate via Intents
.
To asynchronously load and manage the Cursor
the mainActivity
will use a Loader
.
The resulting application will look similar to the following.
8.2. Project
Create the project de.vogella.android.todos
with theActivity
called TodosOverviewActivity
. Create anotherActivity
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 tablepublic 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 statementprivate 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 extendsSQLiteOpenHelper
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@Overridepublic void onCreate(SQLiteDatabase database) {TodoTable.onCreate(database);}// Method is called during an upgrade of the database,// e.g. if you increase the database version@Overridepublic 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 extendsContentProvider
.
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 {// databaseprivate TodoDatabaseHelper database;// Used for the UriMacherprivate 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);}@Overridepublic boolean onCreate() {database = new TodoDatabaseHelper(getContext());return false;}@Overridepublic Cursor query(Uri uri, String[] projection, String selection,String[] selectionArgs, String sortOrder) {// Uisng SQLiteQueryBuilder instead of query() methodSQLiteQueryBuilder queryBuilder = new SQLiteQueryBuilder();// Check if the caller has requested a column which does not existscheckColumns(projection);// Set the tablequeryBuilder.setTables(TodoTable.TABLE_TODO);int uriType = sURIMatcher.match(uri);switch (uriType) {case TODOS:break;case TODO_ID:// Adding the ID to the original queryqueryBuilder.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 notifiedcursor.setNotificationUri(getContext().getContentResolver(), uri);return cursor;}@Overridepublic String getType(Uri uri) {return null;}@Overridepublic 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);}@Overridepublic 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;}@Overridepublic 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 availableif (!availableColumns.containsAll(requestedColumns)) {throw new IllegalArgumentException("Unknown columns in projection");}}}}
MyTodoContentProvider
implements update()
, insert()
, delete()
andquery()
methods. These methods map more or less directly to theSQLiteDatabase
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 theActionBar
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 filepriority.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
underres/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 ourActivities.
The row layout refers to an icon called reminder. Paste an icon of type "png" called "reminder.png" into yourres/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 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 theTodoDetailActivity
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 implementsLoaderManager.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. */@Overridepublic 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@Overridepublic boolean onCreateOptionsMenu(Menu menu) {MenuInflater inflater = getMenuInflater();inflater.inflate(R.menu.listmenu, menu);return true;}// Reaction to the menu selection@Overridepublic boolean onOptionsItemSelected(MenuItem item) {switch (item.getItemId()) {case R.id.insert:createTodo();return true;}return super.onOptionsItemSelected(item);}@Overridepublic 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@Overrideprotected 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 startActivityForResultstartActivityForResult(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@Overrideprotected 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 workString[] from = new String[] { TodoTable.COLUMN_SUMMARY };// Fields on the UI to which we mapint[] 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);}@Overridepublic 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@Overridepublic 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;}@Overridepublic void onLoadFinished(Loader<Cursor> loader, Cursor data) {adapter.swapCursor(data);}@Overridepublic void onLoaderReset(Loader<Cursor> loader) {// data is not available anymore, delete referenceadapter.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;@Overrideprotected 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 InstancetodoUri = (bundle == null) ? null : (Uri) bundle.getParcelable(MyTodoContentProvider.CONTENT_ITEM_TYPE);// Or passed from the other activityif (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 cursorcursor.close();}}protected void onSaveInstanceState(Bundle outState) {super.onSaveInstanceState(outState);saveState();outState.putParcelable(MyTodoContentProvider.CONTENT_ITEM_TYPE, todoUri);}@Overrideprotected 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 availableif (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 todotodoUri = getContentResolver().insert(MyTodoContentProvider.CONTENT_URI, values);} else {// Update todogetContentResolver().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 theTodoDetailActivity
. 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 secondActivity
.
9. Accessing SQLite databases directly
9.1. 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.
9.2. 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 directorycd /data/data# Our applicationcd de.vogella.android.todos# Switch to the database dircd databases# Check the contentls# Assuming that there is a todotable file# connect to this tablesqlite3 todotable.db
The most important commands are:
Table 2. SQlite commands
You find the complete documentation of SQlite at http://www.sqlite.org/sqlite.html .
10. More on ListViews
Please see Android ListView Tutorial for an introduction into ListViews
and ListActivities
.
11. Get the Kindle edition
This tutorial is available for your Kindle.
12. Questions and Discussion
Before posting questions, please see the vogella FAQ. If you have questions or find an error in this article please use thewww.vogella.com Google Group. I have created a short listhow to create good questions which might also help you.
13. Links and Literature
13.1. Source Code
Source Code of Examples
13.2. Android SQLite resources
SQlite website
SQL Tutorial
SQLiteManager Eclipse Plug-in
13.3. Android Resources
Android Tutorial
ListView Tutorial
Intents
Android Background Processing Tutorial
Android Location API and Google Maps
Android and Networking
13.4. vogella Resources
vogella TrainingAndroid and Eclipse Training from the vogella team
Android TutorialIntroduction to Android Programming
GWT TutorialProgram in Java and compile to JavaScript and HTML
Eclipse RCP TutorialCreate native applications in Java
JUnit TutorialTest your application
Git TutorialPut everything you have under distributed version control system
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