Android CRUD + ListView

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:orientation="vertical"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:gravity="center_horizontal"
    tools:context=".MainActivity" >

    <LinearLayout
        android:id="@+id/linearLayout2"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_marginBottom="23dp"
        android:orientation="vertical">

        <EditText
            android:id="@+id/productName"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_marginBottom="28dp"
            android:ems="10"
            android:hint="Name"
            android:inputType="text"
            android:text="" />

        <EditText
            android:id="@+id/productQuantity"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_marginBottom="28dp"
            android:ems="10"
            android:hint="Quantity"
            android:inputType="number" />

        <TextView
            android:id="@+id/productId"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="" />

    </LinearLayout>

    <LinearLayout
        android:id="@+id/linearLayout"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_marginStart="8dp"
        android:layout_marginEnd="8dp"
        android:layout_marginBottom="36dp"
        android:orientation="horizontal">

        <Button
            android:id="@+id/btn_find"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:onClick="findProduct"
            android:text="@string/find_string"
            tools:layout_editor_absoluteX="4dp"
            tools:layout_editor_absoluteY="401dp" />

        <Button
            android:id="@+id/btn_delete"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:onClick="deleteProduct"
            android:text="@string/delete_string"
            tools:layout_editor_absoluteX="140dp"
            tools:layout_editor_absoluteY="413dp" />

        <Button
            android:id="@+id/btn_add"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:onClick="addProduct"
            android:text="@string/add_string"
            tools:layout_editor_absoluteX="296dp"
            tools:layout_editor_absoluteY="341dp" />
    </LinearLayout>

    <ListView
        android:padding="5dp"
        android:id="@+id/product_list"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:dividerHeight="2dp" />

</LinearLayout>

DBHandler.java

package com.vokasi.basisdatamobile;

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;
import java.util.HashMap;
import java.util.Queue;

public class DBHandler extends SQLiteOpenHelper {

    private static final int DATABASE_VERSION=1;
    private static final String DATABASE_NAME = "product.db";
    private static final String TABLE_PRODUCTS = "products";

    public static final String COLUMN_ID = "_id";
    public static final String COLUMN_NAME = "_name";
    public static final String COLUMN_QUANTITY = "_quantity";

    public DBHandler(Context context, String name, SQLiteDatabase.CursorFactory factory, int version) {
        super(context, DATABASE_NAME, factory, DATABASE_VERSION);
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        String CREATE_PRODUCTS_TABLE = "CREATE TABLE "+ TABLE_PRODUCTS + "(" + COLUMN_ID
                + " INTEGER PRIMARY KEY AUTOINCREMENT,"+ COLUMN_NAME
                + " TEXT,"+ COLUMN_QUANTITY +" INTEGER "+")";
        db.execSQL(CREATE_PRODUCTS_TABLE);
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        db.execSQL("DROP TABLE IF EXISTS "+ TABLE_PRODUCTS);
        onCreate(db);
    }

    public void addProduct(Product product){
        ContentValues values = new ContentValues();
        values.put(COLUMN_NAME, product.get_name());
        values.put(COLUMN_QUANTITY, product.get_quantity());

        SQLiteDatabase db = this.getWritableDatabase();
        db.insert(TABLE_PRODUCTS,null,values);
        db.close();
    }

    public Product findProduct(String productname){
        String query = "SELECT * FROM "+ TABLE_PRODUCTS +
                        " WHERE "+COLUMN_NAME+" = \""+ productname + "\"";

        SQLiteDatabase db = this.getWritableDatabase();
        Cursor cursor = db.rawQuery(query,null);
        Product product = new Product();


        if (cursor.moveToFirst()){
            cursor.moveToFirst();
            product.set_id(Integer.parseInt(cursor.getString(0)));
            product.set_name(cursor.getString(1));
            product.set_quantity(Integer.parseInt(cursor.getString(2)));
            cursor.close();
        }else{
            product = null;
        }

        db.close();
        return product;

    }

    public boolean deleteProduct (String productname){
        boolean result = false;

        String query = "SELECT * FROM "+ TABLE_PRODUCTS +
                " WHERE "+COLUMN_NAME+" = \""+ productname + "\"";

        SQLiteDatabase db = this.getWritableDatabase();
        Cursor cursor = db.rawQuery(query,null);
        Product product = new Product();

        if (cursor.moveToFirst()){
            cursor.moveToFirst();
            product.set_id(Integer.parseInt(cursor.getString(0)));
            db.delete(TABLE_PRODUCTS,COLUMN_ID+ " = ?",
                    new String[]{String.valueOf(product.get_id()) });
            cursor.close();
            result = true;
        }else{
            product = null;
        }



        db.close();
        return result;

    }

    public ArrayList<HashMap<String,String>> allProducts(){
        ArrayList<HashMap<String,String>> productList= new ArrayList<>();
        SQLiteDatabase db = this.getWritableDatabase();
        String query = "SELECT * FROM "+TABLE_PRODUCTS;
        Cursor cursor = db.rawQuery(query,null);
        while(cursor.moveToNext()){
            HashMap<String,String> product = new HashMap<>();
            product.put("id",cursor.getString(cursor.getColumnIndex(COLUMN_ID)));
            product.put("name",cursor.getString(cursor.getColumnIndex(COLUMN_NAME)));
            product.put("quantity",cursor.getString(cursor.getColumnIndex(COLUMN_QUANTITY)));
            productList.add(product);
        }
        return productList;
    }

}

MainActivity.java

package com.vokasi.basisdatamobile;

import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.util.Log;
import android.view.View;
import android.widget.EditText;
import android.widget.ListAdapter;
import android.widget.ListView;
import android.widget.SimpleAdapter;
import android.widget.TextView;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.HashMap;

public class MainActivity extends AppCompatActivity {

    TextView productId;
    EditText productName;
    EditText productQuantity;
    ListView productListView;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        productId = (TextView) findViewById(R.id.productId);
        productName = (EditText) findViewById(R.id.productName);
        productQuantity = (EditText) findViewById(R.id.productQuantity);
        productListView = (ListView) findViewById(R.id.product_list);

        DBHandler handler = new DBHandler(this,null,null,1);
        final ArrayList<HashMap<String,String>> productList =  handler.allProducts();

        String from[]={"id","name","quantity"};
        int to[]={R.id.product_id,R.id.product_name,R.id.product_quantity};

        ListAdapter adapter = new SimpleAdapter(MainActivity.this,productList,R.layout.product_list,from,to);
        productListView.setAdapter(adapter);

    }



    public void addProduct(View view){
        DBHandler productHandler = new DBHandler(this,null,null,1);
        int qty = Integer.parseInt(productQuantity.getText().toString());
        String name = productName.getText().toString();

        Product product = new Product(name,qty);
        productHandler.addProduct(product);

        productName.setText("");
        productQuantity.setText("");
        DBHandler handler = new DBHandler(this,null,null,1);
        ArrayList<HashMap<String,String>> productList =  handler.allProducts();

        String from[]={"id","name","quantity"};
        int to[]={R.id.product_id,R.id.product_name,R.id.product_quantity};

        ListAdapter adapter = new SimpleAdapter(MainActivity.this,productList,R.layout.product_list,from,to);
        productListView.setAdapter(adapter);
        Log.d("this is my array", "arr: " + productList.toString());
    }

    public void findProduct(View view){
        DBHandler productHandler = new DBHandler(this,null,null,1);
        String name = productName.getText().toString();

        Product product = productHandler.findProduct(name);
        if (product != null){
            productId.setText(String.valueOf(product.get_id()));
            productQuantity.setText(String.valueOf(product.get_quantity()));
        }else{
            productId.setText("No match found");
        }
    }

    public void deleteProduct(View view){
        DBHandler handler = new DBHandler(this,null,null,1);
        String name = productName.getText().toString();
        boolean result = handler.deleteProduct(name);
        if (result){
            productId.setText("Record deleted");
            productName.setText("");
            productQuantity.setText("");
        }else{
            productId.setText("No match found");
        }

        ArrayList<HashMap<String,String>> productList =  handler.allProducts();

        String from[]={"id","name","quantity"};
        int to[]={R.id.product_id,R.id.product_name,R.id.product_quantity};

        ListAdapter adapter = new SimpleAdapter(MainActivity.this,productList,R.layout.product_list,from,to);
        productListView.setAdapter(adapter);
    }
}

Product.java

package com.vokasi.basisdatamobile;

public class Product {
    private int _id;
    private String _name;
    private int _quantity;

    public Product(String _name, int _quantity) {
        this._name = _name;
        this._quantity = _quantity;
    }

    public Product() {
    }

    public int get_id() {
        return _id;
    }

    public void set_id(int _id) {
        this._id = _id;
    }

    public String get_name() {
        return _name;
    }

    public void set_name(String _name) {
        this._name = _name;
    }

    public int get_quantity() {
        return _quantity;
    }

    public void set_quantity(int _quantity) {
        this._quantity = _quantity;
    }
}

product_list.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent" android:layout_height="match_parent">

    <TextView
        android:id="@+id/product_name"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textStyle="bold"
        android:textSize="16dp"
        android:text="Name" />

    <TextView
        android:id="@+id/product_id"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_below="@id/product_name"
        android:textSize="14dp"
        android:text="Id" />

    <TextView
        android:id="@+id/product_quantity"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignBaseline="@id/product_id"
        android:layout_alignBottom="@id/product_id"
        android:layout_alignParentRight="true"
        android:text="Quantity" />
</RelativeLayout>