Introduction :
Often, there is a need to initiate an Android app with an already existing database. This is called prepopulating a database. In this article, we will see how to pre-populate database in Android using SQLite Database. The database used in this example can be downloaded as Demo Database.
To prepopulate a SQLite database in an Android application, you can follow these steps:
- Create a new SQLite database in your Android application.
- Create a SQL script that contains the data you want to prepopulate your database with. This script should contain the SQL commands to create tables, insert data, and perform other database operations.
- Store the SQL script in the assets folder of your Android application.
- In the onCreate() method of your SQLiteOpenHelper subclass, open the database and execute the SQL script to populate the database with data.
Here is an example code snippet that demonstrates how to prepopulate a SQLite database in an Android application :
Java
import android.content.Context;import android.database.sqlite.SQLiteDatabase;import android.database.sqlite.SQLiteOpenHelper;public class MyDatabaseHelper extends SQLiteOpenHelper { private final Context context; private static final String DATABASE_NAME = "myDatabase.db"; private static final int DATABASE_VERSION = 1; public MyDatabaseHelper(Context context) { super(context, DATABASE_NAME, null, DATABASE_VERSION); this.context = context; } @Override public void onCreate(SQLiteDatabase db) { String createTableQuery = "CREATE TABLE myTable (id INTEGER PRIMARY KEY, name TEXT)"; db.execSQL(createTableQuery); } @Override public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) { db.execSQL("DROP TABLE IF EXISTS myTable"); onCreate(db); } @Override public void onOpen(SQLiteDatabase db) { super.onOpen(db); } public void insertData(int id, String name) { SQLiteDatabase db = getWritableDatabase(); String insertDataQuery = "INSERT INTO myTable VALUES (" + id + ", '" + name + "')"; db.execSQL(insertDataQuery); db.close(); }} |
Approach:
- Add the support Library in build.gradle file and add Recycler View dependency in the dependencies section.
XML
dependencies{ implementation 'androidx.recyclerview:recyclerview:1.1.0'} |
- Make sure you add the database in assets folder. To create assets folder right click on app directory->new->Folder->(select)Assets Folder. Then simply paste your .db file in assets folder.
- In activity_main.xml, add the following code.
XML
<?xml version="1.0" encoding="utf-8"?><LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="match_parent" android:layout_height="match_parent" android:paddingStart="5dp" android:paddingTop="5dp"> <androidx.recyclerview.widget.RecyclerView android:id="@+id/my_recycler_view" android:layout_width="match_parent" android:layout_height="match_parent" android:scrollbars="vertical"/></LinearLayout> |
- Create a new custom_layout.xml file with the following code.
XML
<?xml version="1.0" encoding="utf-8"?><LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="match_parent" android:layout_height="wrap_content" android:layout_marginTop="3dp" > <TextView android:textStyle="bold" android:layout_margin="5dp" android:textSize="20sp" android:layout_width="match_parent" android:layout_height="wrap_content" android:id="@+id/textView"/></LinearLayout> |
- Create a DatabaseHelper class and add the following code.
Java
package org.neveropen.dictionary;import android.app.Activity;import android.content.Context;import android.database.Cursor;import android.database.sqlite.SQLiteDatabase;import android.database.sqlite.SQLiteException;import android.database.sqlite.SQLiteOpenHelper;import android.util.Log;import java.io.FileOutputStream;import java.io.IOException;import java.io.InputStream;import java.io.OutputStream;import java.sql.SQLException;import java.util.ArrayList;import java.util.List;public class DatabaseHelper extends SQLiteOpenHelper { // The Android's default system path // of your application database. private static String DB_PATH = ""; private static String DB_NAME = "database.db"; private SQLiteDatabase myDataBase; private final Context myContext; private SQLiteOpenHelper sqLiteOpenHelper; // Table name in the database. public static final String ALGO_TOPICS = "algo_topics"; /** * Constructor * Takes and keeps a reference of * the passed context in order * to access the application assets and resources. */ public DatabaseHelper(Context context) { super(context, DB_NAME, null, 1); this.myContext = context; DB_PATH = myContext.getDatabasePath(DB_NAME) .toString(); } // Creates an empty database // on the system and rewrites it // with your own database. public void createDataBase() throws IOException { boolean dbExist = checkDataBase(); if (dbExist) { // do nothing - database already exist } else { // By calling this method and // the empty database will be // created into the default system // path of your application // so we are gonna be able // to overwrite that database // with our database. this.getWritableDatabase(); try { copyDataBase(); } catch (IOException e) { throw new Error( "Error copying database"); } } } // Check if the database already exist // to avoid re-copying the file each // time you open the application // return true if it exists // false if it doesn't. private boolean checkDataBase() { SQLiteDatabase checkDB = null; try { String myPath = DB_PATH; checkDB = SQLiteDatabase .openDatabase( myPath, null, SQLiteDatabase.OPEN_READONLY); } catch (SQLiteException e) { // database doesn't exist yet. Log.e("message", "" + e); } if (checkDB != null) { checkDB.close(); } return checkDB != null; } /** * Copies your database from your * local assets-folder to the just * created empty database in the * system folder, from where it * can be accessed and handled. * This is done by transferring bytestream. * */ private void copyDataBase() throws IOException { // Open your local db as the input stream InputStream myInput = myContext.getAssets() .open(DB_NAME); // Path to the just created empty db String outFileName = DB_PATH; // Open the empty db as the output stream OutputStream myOutput = new FileOutputStream(outFileName); // transfer bytes from the // inputfile to the outputfile byte[] buffer = new byte[1024]; int length; while ((length = myInput.read(buffer)) > 0) { myOutput.write(buffer, 0, length); } // Close the streams myOutput.flush(); myOutput.close(); myInput.close(); } public void openDataBase() throws SQLException { // Open the database String myPath = DB_PATH; myDataBase = SQLiteDatabase .openDatabase( myPath, null, SQLiteDatabase.OPEN_READONLY); } @Override public synchronized void close() { // close the database. if (myDataBase != null) myDataBase.close(); super.close(); } @Override public void onCreate(SQLiteDatabase db) { // It is an abstract method // but we define our own method here. } @Override public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) { // It is an abstract method which is // used to perform different task // based on the version of database. } // This method is used to get the // algorithm topics from the database. public List<String> getAlgorithmTopics( Activity activity) { sqLiteOpenHelper = new DatabaseHelper(activity); SQLiteDatabase db = sqLiteOpenHelper .getWritableDatabase(); List<String> list = new ArrayList<>(); // query help us to return all data // the present in the ALGO_TOPICS table. String query = "SELECT * FROM " + ALGO_TOPICS; Cursor cursor = db.rawQuery(query, null); if (cursor.moveToFirst()) { do { list.add(cursor.getString(1)); } while (cursor.moveToNext()); } return list; }} |
- Create a MyAdapter.java class and add the following code.
Java
package org.neveropen.dictionary;import android.app.Activity;import android.view.LayoutInflater;import android.view.View;import android.view.ViewGroup;import android.widget.TextView;import androidx.annotation.NonNull;import androidx.recyclerview.widget.RecyclerView;import java.util.List;public class MyAdapter extends RecyclerView.Adapter<MyAdapter.ViewHolder> { private List<String> data; Activity activity; public MyAdapter(Activity activity, List<String> data) { this.data = data; this.activity = activity; } // This method is used to attach // custom layout to the recycler view @NonNull @Override public ViewHolder onCreateViewHolder( @NonNull ViewGroup parent, int viewType) { LayoutInflater LI = activity.getLayoutInflater(); View vw = LI.inflate( R.layout.custom_layout, null); return new ViewHolder(vw); } // This method is used to set the action // to the widgets of our custom layout. @Override public void onBindViewHolder( @NonNull ViewHolder holder, int position) { holder.topic_name .setText(data.get(position)); } @Override public int getItemCount() { return data.size(); } class ViewHolder extends RecyclerView.ViewHolder { TextView topic_name; public ViewHolder(View itemView) { super(itemView); this.topic_name = itemView.findViewById(R.id.textView); } }} |
- Finally, in MainActivity.java add the following code.
Java
package org.neveropen.algorithmTopics;import androidx.appcompat.app.AppCompatActivity;import androidx.recyclerview.widget.DefaultItemAnimator;import androidx.recyclerview.widget.LinearLayoutManager;import androidx.recyclerview.widget.RecyclerView;import android.os.Bundle;import java.util.ArrayList;import java.util.List;public class MainActivity extends AppCompatActivity { private static RecyclerView.Adapter adapter; private static RecyclerView recyclerView; public static List<String> data; DatabaseHelper db; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); recyclerView = findViewById(R.id.my_recycler_view); db = new DatabaseHelper(this); recyclerView.setLayoutManager( new LinearLayoutManager(this)); data = new ArrayList<>(); fetchData(); } public void fetchData() { // Before fetching the data // directly from the database. // first we have to creates an empty // database on the system and // rewrites it with your own database. // Then we have to open the // database to fetch the data from it. db = new DatabaseHelper(this); try { db.createDataBase(); db.openDataBase(); } catch (Exception e) { e.printStackTrace(); } data = db.getAlgorithmTopics(this); adapter = new MyAdapter(this, data); recyclerView.setAdapter(adapter); }} |
Output: 
