Create Database Helper Class
Description
A good practice for dealing with databases is to create a helper class to encapsulate all the complexities of accessing the data.
Example
package com.java2s.myapplication3.app;
// ww w. j a va 2 s . c o m
import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.SQLException;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import android.util.Log;
public class DBAdapter {
static final String KEY_ROWID = "_id";
static final String KEY_NAME = "name";
static final String KEY_EMAIL = "email";
static final String TAG = "DBAdapter";
static final String DATABASE_NAME = "MyDB";
static final String DATABASE_TABLE = "contacts";
static final int DATABASE_VERSION = 1;
static final String DATABASE_CREATE =
"create table contacts (_id integer primary key autoincrement, "
+ "name text not null, email text not null);";
final Context context;
DatabaseHelper DBHelper;
SQLiteDatabase db;
public DBAdapter(Context ctx)
{
this.context = ctx;
DBHelper = new DatabaseHelper(context);
}
private static class DatabaseHelper extends SQLiteOpenHelper
{
DatabaseHelper(Context context)
{
super(context, DATABASE_NAME, null, DATABASE_VERSION);
}
@Override
public void onCreate(SQLiteDatabase db)
{
try {
db.execSQL(DATABASE_CREATE);
} catch (SQLException e) {
e.printStackTrace();
}
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion)
{
Log.w(TAG, "Upgrading database from version " + oldVersion + " to "
+ newVersion + ", which will destroy all old data");
db.execSQL("DROP TABLE IF EXISTS contacts");
onCreate(db);
}
}
//opens the database
public DBAdapter open() throws SQLException
{
db = DBHelper.getWritableDatabase();
return this;
}
//closes the database
public void close()
{
DBHelper.close();
}
//insert a contact into the database
public long insertContact(String name, String email)
{
ContentValues initialValues = new ContentValues();
initialValues.put(KEY_NAME, name);
initialValues.put(KEY_EMAIL, email);
return db.insert(DATABASE_TABLE, null, initialValues);
}
//deletes a particular contact
public boolean deleteContact(long rowId)
{
return db.delete(DATABASE_TABLE, KEY_ROWID + "=" + rowId, null) > 0;
}
//retrieves all the contacts
public Cursor getAllContacts()
{
return db.query(DATABASE_TABLE, new String[] {KEY_ROWID, KEY_NAME,
KEY_EMAIL}, null, null, null, null, null);
}
//retrieves a particular contact
public Cursor getContact(long rowId) throws SQLException
{
Cursor mCursor =
db.query(true, DATABASE_TABLE, new String[] {KEY_ROWID,
KEY_NAME, KEY_EMAIL}, KEY_ROWID + "=" + rowId, null,
null, null, null, null);
if (mCursor != null) {
mCursor.moveToFirst();
}
return mCursor;
}
//updates a contact
public boolean updateContact(long rowId, String name, String email)
{
ContentValues args = new ContentValues();
args.put(KEY_NAME, name);
args.put(KEY_EMAIL, email);
return db.update(DATABASE_TABLE, args, KEY_ROWID + "=" + rowId, null) > 0;
}
}
Add Contacts
The following code demonstrates how you can add a contact to the table.
import android.app.Activity;
import android.os.Bundle;
/*from w w w . jav a2s.c o m*/
public class DatabasesActivity extends Activity {
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
DBAdapter db = new DBAdapter(this);
//add a contact
db.open();
long id = db.insertContact("Jack", "xml@example.com");
id = db.insertContact("Jane", "html@example.com");
db.close();
}
}
Retrieve All the Contacts
import android.app.Activity;
import android.database.Cursor;
import android.os.Bundle;
import android.widget.Toast;
// w w w . j av a 2 s . c o m
public class DatabasesActivity extends Activity {
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
DBAdapter db = new DBAdapter(this);
//get all contacts
db.open();
Cursor c = db.getAllContacts();
if (c.moveToFirst())
{
do {
DisplayContact(c);
} while (c.moveToNext());
}
db.close();
}
public void DisplayContact(Cursor c)
{
Toast.makeText (this,
"id: " + c.getString(0) + "\n" +
"Name: " + c.getString(1) + "\n" +
"Email: " + c.getString(2),
Toast.LENGTH_LONG).show();
}
}
Retrieve a Single Contact
@Override//from w w w. j a v a 2 s.c om
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
DBAdapter db = new DBAdapter(this);
//get a contact
db.open();
Cursor c = db.getContact(2);
if (c.moveToFirst())
DisplayContact(c);
else
Toast.makeText (this, "No contact found", Toast.LENGTH_LONG).show();
db.close();
}
Update a Contact
@Override/*from www . j av a 2 s. c o m*/
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
DBAdapter db = new DBAdapter(this);
//update contact
db.open();
if (db.updateContact(1, "XML", "XML@example.com"))
Toast.makeText (this, "Update successful.", Toast.LENGTH_LONG).show();
else
Toast.makeText (this, "Update failed.", Toast.LENGTH_LONG).show();
db.close();
}
Delete a Contact
@Override//from www .jav a 2 s . c o m
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
DBAdapter db = new DBAdapter(this);
//delete a contact
db.open();
if (db.deleteContact(1))
Toast.makeText (this, "Delete successful.", Toast.LENGTH_LONG).show();
else
Toast.makeText (this, "Delete failed.", Toast.LENGTH_LONG).show();
db.close();
}