Cómo prepoblar la base de datos en Android usando la base de datos SQLite

A menudo, es necesario iniciar una aplicación de Android con una base de datos ya existente. Esto se denomina prepoblar una base de datos . En este artículo, veremos cómo completar previamente la base de datos en Android usando la base de datos SQLite . La base de datos utilizada en este ejemplo se puede descargar como base de datos de demostración .

Acercarse:

1. Agregue la biblioteca de soporte en el archivo build.gradle y agregue la dependencia de Recycler View en la sección de dependencias.

   dependencies{        implementation 'androidx.recyclerview:recyclerview:1.1.0' }

2. Asegúrese de agregar la base de datos en la carpeta de activos. Para crear una carpeta de activos, haga clic con el botón derecho en el directorio de la aplicación->nuevo->Carpeta->(seleccionar)Carpeta de activos . Luego simplemente pegue su archivo .db en la carpeta de activos.
3. En activity_main.xml , agregue el siguiente código.

   <?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>

4. Cree un nuevo archivo custom_layout.xml con el siguiente código.

   <?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>

5. Cree una clase DatabaseHelper y agregue el siguiente código.

   package org.geeksforgeeks.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;     } }

6. Cree una clase MyAdapter.java y agregue el siguiente código.

   package org.geeksforgeeks.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);         }     } }

7. Finalmente, en MainActivity.java agregue el siguiente código.

   package org.geeksforgeeks.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);     } }

Producción: