วันพฤหัสบดีที่ 5 กรกฎาคม พ.ศ. 2555

Android Database

--> Android Database SQLite

SQLite Database
For more complex data structures, a database provides a quicker and more flexible access method than flat files or shared preferences.Android provides a built-in database called SQLite that provides full relational database capability utilizing SQL commands. Each application that uses SQLite has its own instance of the database, which is by default accessible only from the application itself.The database is stored in the /data/data/<package_name>/databases folder of an Android device.A Content Provider can be used to share the database information between applications.The different steps for utilizing SQLite are
1. Create a database.
2. Open the database.
3. Create a table.
4. Create an insert interface for datasets.
5. Create a query interface for datasets.
6. Close the database.
The next recipe provides a general method to accomplish these steps.

Creating a Separate Database Package
A good modular structure to classes is essential for more complicated Android projects. Here, the database class is put in its own package com.cookbook.data so it is easy to reuse.This package contains three classes: MyDB, MyDBhelper, and Constants.
The MyDB class It contains a SQLiteDatabase instance and a MyDBhelper class with the methods that follow:
  • MyDB( )—Initializes a MyDBhelper instance (the constructor).
  • open( )—Initializes a SQLiteDatabase instance using the MyDBhelper.This opens a writeable database connection. If SQLite throws any exception, it tries to get a readable database instead.
  • close( )—Closes the database connection.
  • insertdiary( )—Saves a diary entry to the database as name-value pairs in a ContentValues instance, and then passes the data to the SQLitedatabase instance to do an insert.
  • getdiaries( )—Reads the diary entries from the database, saves them in a Cursor class, and returns it from the method.
Android Database Example Code
DataBaseSQLActivity.java Code
package android.example.database;

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 DataBaseSQLActivity 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();
            }  
}

MySQLiteHelper.java Code
package android.example.database;

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);
      }

}

CommentsDataSource.java Code
package android.example.database;

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);
            //values.put(MySQLiteHelper.COLUMN_FILE, comment);
           
            long insertId = database.insert(MySQLiteHelper.TABLE_COMMENTS, null,
                        values);
            Cursor cursor = database.query(MySQLiteHelper.TABLE_COMMENTS,
                        allColumns, MySQLiteHelper.COLUMN_ID + " = " + insertId, null,
                        null, null, null);
            cursor.moveToFirst();
            Comment newComment = cursorToComment(cursor);
            cursor.close();
            return newComment;
      }

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

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

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

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

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

Comment.java Code

package android.example.database;

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;
      }    
}

main.xml Code
<?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:background="#094601"
    android:orientation="vertical" >

  <TextView
        android:id="@+id/textView1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center_horizontal"
        android:layout_marginBottom="5dp"
        android:layout_marginTop="5dp"
        android:text="Database SQLite Example" />

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

        <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:background="#75df67"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:text="@string/hello" />

</LinearLayout>


Download Android Database Example Code -->




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