Creating and inserting into a database

Question

I'm trying to create a basic database and insert three users, but it doesn't work.

This is a class that creates the database

package com.example.matadoor.db1;

import android.content.Context;
import android.database.DatabaseErrorHandler;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;

/**
* Created by matadoor on 06/08/2016.
*/
public class dbcreat extends SQLiteOpenHelper {

    public final String tbname="t1";
    public final String cid="id";
    public static String cid2="test";
    public final String user="username";

    public final String creat="CREATE TABLE "+cid2+"("+cid+"INTEGER primery key AUTO_INCREMENT , "+user+" TEXT); ";

    public dbcreat(Context context) {
        super(context,cid2,null, 1);
    }

    public dbcreat(Context context, String name, SQLiteDatabase.CursorFactory factory, int version, DatabaseErrorHandler errorHandler) {
        super(context, name, factory, version, errorHandler);
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        db.execSQL(creat);
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion)     {

}

And it's the other class which handles the database - opens it, closes it, and inserts into it

package com.example.matadoor.db1;

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

/**
* Created by matadoor on 08/08/2016.
*/
public class dbhandler {

    private dbcreat dbc;
    private SQLiteDatabase sdb;

    public  dbhandler(Context context)
    {
        dbc=new dbcreat(context);
    }

    public void open()
    {
        sdb=dbc.getWritableDatabase();
    }

    public void close(){
        dbc.close();
    }

    public String display(int row)
    {
        Cursor cu=sdb.query(dbc.tbname,null,null,null,null,null,null);
        cu.moveToPosition(row);
        String user=cu.getString(1);
        return user;
    }


    public void insert(String user)
    {
        ContentValues cn=new ContentValues();
        cn.put(dbc.user,user);
    }
}

And the main class which has one Button for inserting a user into the db

package com.example.matadoor.db1;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;

public class Main extends AppCompatActivity {

    Button btn;
    dbhandler db;

    dbcreat dbc;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);

        btn=(Button)findViewById(R.id.ins);

       // dbc.getWritableDatabase();
        db.open();

        db=new dbhandler(this);
        btn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                String [] user={"ali","reza","ahmed"};

                for(int i=0;i<user.length;i++)
                {
                    db.insert(user[i]);
                }
            }
        });

     }
}

Sorry, but you have to be more specific about **what** doesn't work. Is there an error? If so, please [edit] the question — OneCricketeer, Aug 08 '16 at 18:59

score 0 · Accepted Answer · answered Aug 08 '16 at 19:04

So this seems to be a error. You need to switch those two lines.

    db.open(); // NullPointer here

    db=new dbhandler(this);

Assuming there are no other errors with the code, this method is doing nothing to the database.

public void insert(String user)
{
    ContentValues cn=new ContentValues();
    cn.put(dbc.user,user);
}

You have to call sdb.insert with that cn variable.

Creating and inserting into a database

1 Answers1