fabioacarvalho/app-java-mobila-example-crud

Example of CRUD in App with Java and SQLite

Example of CRUD in App with Java and SQLite

Start here

You need to have Android Studio instaled in your developer envirioment.

First step

In the first step, you need to create a file Class where you'll references your instance, for example:

In this case I'll use a example of add cities. But you are free to create what you want.

package com.example.sqliteapplication;

import android.util.Log;

public class City {

    public long id;
    public String name;
    public int population;

    public City(long id, String name, int population) {
        this.id = id;
        this.name = name;
        this.population = population;
    }

    public City(String name, int population) {
        id = -1;
        this.name = name;
        this.population = population;
    }

    public void print(){
        Log.v("SQLDatabase", "City["+id+"]:"+name);
    }

}

Name file: City.java

Second step

Now we'll create a Class of Database. In this file we'll create the CRUD:

• Create our Table:

package com.example.sqliteapplication;

import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;

import java.util.ArrayList;

public class CityDatabase extends SQLiteOpenHelper {

    private static final String DB_NAME = "cities.sqlite";
    private static final int DB_VERSION = 1;

    // Database Table
    private static String DB_TABLE = "City";
    private static String COL_ID = "id";
    private static String COL_NAME = "name";
    private static String COL_POPULATION = "population";

    private Context context;
    public CityDatabase(Context context){
        super(context, DB_NAME, null, DB_VERSION);
    }

    @Override
    public void onCreate(SQLiteDatabase sqLiteDatabase) {
        String query = "Create Table if not exists " + DB_TABLE + "( "+
                COL_ID + " Integer primary key autoincrement, " +
                COL_NAME + " TEXT, " +
                COL_POPULATION + " INTEGER" + ")";
        sqLiteDatabase.execSQL(query);
    }

}

Name file: CityDatabase.java

• CREATE Method:

    public long createCityInDB(City c){
        SQLiteDatabase database = getWritableDatabase();
        ContentValues values = new ContentValues();
        values.put(COL_NAME,c.name);
        values.put(COL_POPULATION,""+c.population);
        long id = database.insert(DB_TABLE, null, values);
        database.close();
        return  id;
    }

• GET Method:

 public ArrayList<City> getCitiesFromDB(){
    ArrayList<City> cities = new ArrayList<>();

    SQLiteDatabase database = getReadableDatabase();

    // Criar um cursor de localizacao da tabela:
    // database.query.(DB_TABLE, column, selection, selectionArgs, groupBy, having, orderBy):
    Cursor cursor = database.query(DB_TABLE, null, null, null, null,null, null);

    if(cursor.moveToFirst()){
        do{
            long id = cursor.getLong(cursor.getColumnIndexOrThrow(COL_ID));
            String name = cursor.getString(cursor.getColumnIndexOrThrow(COL_NAME));
            int population = cursor.getInt(cursor.getColumnIndexOrThrow(COL_POPULATION));
            cities.add(
                    new City(id, name, population)
            );
        } while (cursor.moveToNext());
        database.close();
    }

    return cities;
}

• UPDATE Method:

public int updateCityInDB(City c){
    SQLiteDatabase database = getWritableDatabase();
    ContentValues values = new ContentValues();
    values.put(COL_NAME, c.name);
    values.put(COL_POPULATION, c.population);
    String id = String.valueOf(c.id);
    int count = database.update(DB_TABLE, values, COL_ID + "=?", new String[]{id});
    database.close();

    return count;
}

• DELETE Method:

public int removeCityInDB(City c){
    SQLiteDatabase database = getWritableDatabase();
    String id = String.valueOf(c.id);
    int count = database.delete(DB_TABLE, COL_ID + "=?", new String[]{id});
    database.close();
    return count;
}

Third step

Now we'll load ours data in the listView.

Into MainActivity.class in the method onCreate we can create the following code:

public class MainActivity extends AppCompatActivity {
    ListView listView;
    ArrayList<String> items = new ArrayList<>();


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        listView = findViewById(R.id.listView);

        loadListFromDB();

    }

    void loadListFromDB(){
        CityDatabase database = new CityDatabase(MainActivity.this);
        ArrayList<City> cities = database.getCitiesFromDB();
        for (City c:cities){
            items.add(c.id + "- " + c.name);
            c.print();
        }
    }
}

The method loadListFromDB will load ours data and add in the listView, but before you need create a listView in your file.xml.