Nullpointerexception when trying to insert a value into SQLite

Question

I'm trying to insert some values into an SQLite Database which are entered by the user, however when I press the button to save the values it crashes and a NullPointer exception is thrown:

java.lang.NullPointerException: Attempt to invoke virtual method 'long android.database.sqlite.SQLiteDatabase.insert(java.lang.String, java.lang.String, android.content.ContentValues)' on a null object reference at com.example.w4e74.farmanimalfinal.DatabaseHelper.insertRecord(DatabaseHelper.java:61)at com.example.w4e74.farmanimalfinal.Activity_item.onOptionsItemSelected(Activity_item.java:66)

I do not know what is causing the exception. My code is below, any help would be very appreciated.

Activity_item.java

package com.example.w4e74.farmanimalfinal;

import android.app.Dialog;
import android.content.Intent;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import android.support.v7.app.ActionBar;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.support.v7.widget.Toolbar;
import android.view.Menu;
import android.view.MenuItem;
import android.view.ViewDebug;
import android.widget.EditText;
import android.widget.ListView;

public class Activity_item extends AppCompatActivity {

EditText editText_item;
boolean newItem;
long item_index;

private SQLiteDatabase db;
private Cursor cursor;
CustomCursorAdapter listAdapter;

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

    DatabaseHelper db = new DatabaseHelper(this);

    Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar_item);
    setSupportActionBar(toolbar);

    ActionBar actionBar = getSupportActionBar();
    actionBar.setDisplayHomeAsUpEnabled(true);



    Intent intent = getIntent();
    item_index = intent.getLongExtra("item_index", -1);

    if(item_index == -1) {
        newItem = true;
    } else {

        newItem = false;
    }
}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    getMenuInflater().inflate(R.menu.menu_item, menu);
    return super.onCreateOptionsMenu(menu);
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    switch (item.getItemId()) {
        case R.id.save_item:


            DatabaseHelper.insertRecord(db, (R.id.editText_date),(R.id.editText_time), Integer.toString(R.id.editText_staff),(R.id.editText_animal),Integer.toString(R.id.editText_activity),Integer.toString(R.id.editText_details));

            finish();
            return true;


        default:
            return super.onOptionsItemSelected(item);
    }
}

}

DatabaseHelper.java

package com.example.w4e74.farmanimalfinal;

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

public class DatabaseHelper extends SQLiteOpenHelper {

private static final String DB_NAME = "farmanimals";

private static final int DB_VERSION = 1;

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

@Override
public void onCreate(SQLiteDatabase db) {
    db.execSQL("CREATE TABLE RECORD ("
            + "_id INTEGER PRIMARY KEY AUTOINCREMENT, "
            + "DATE INTEGER, "
            + "TIME INTEGER, "
            + "STAFF TEXT,"
            + "ANIMAL INTEGER,"
            + "ACTIVITY TEXT,"
            + "DETAIL TEXT);"
    );



}

@Override
public void onUpgrade(SQLiteDatabase sqLiteDatabase, int i, int i1) {

}

@Override
public void onDowngrade(SQLiteDatabase sqLiteDatabase, int i, int i1) {


}


public static long insertRecord(SQLiteDatabase db, int date, int time, String staff, int animal, String activity, String detail ) {

    ContentValues recordValues = new ContentValues();


    recordValues.put("DATE", date);
    recordValues.put("TIME", time);
    recordValues.put("STAFF", staff);
    recordValues.put("ANIMAL", animal);
    recordValues.put("ACTIVITY", activity);
    recordValues.put("DETAIL", detail);


    long newRecordID = db.insert("RECORD", null, recordValues);

    return newRecordID;
}

public static String getDatabaseContentsAsString(SQLiteDatabase db) {

    Cursor cursor = db.query("RECORD",
            new String[]{"_id", "DATE", "TIME", "STAFF", "ANIMAL", "ACTIVITY", "DETAIL"},
            null, null, null, null, "_id ASC");

    String databaseAsString = System.getProperty("line.separator");

    if(cursor.getCount() != 0) {
        cursor.moveToFirst();
        while (!cursor.isAfterLast()) {
            for (int i=0; i < cursor.getColumnCount() - 1; i++) {
                databaseAsString += cursor.getString(i) + "     ";
            }
            databaseAsString += System.getProperty("line.separator");
            cursor.moveToNext();
        }

        if(cursor != null) cursor.close();
    }

    return databaseAsString;
}


public static void deleteRecord(SQLiteDatabase db, Long id) {
    db.delete("RECORD", "_id=?", new String[] {Long.toString(id)});
}

public static void deleteAllRecords(SQLiteDatabase db) {
    db.delete("RECORD", null, null);
    db.delete("SQLITE_SEQUENCE","NAME = ?",new String[]{"RECORD"});
}

}

Edit: Error message received:

Incompatible types.
Required:
android.database.sqlite.SQLiteDatabase
Found:
com.example.w4e74.farmanimalfinal.DatabaseHelper

Possible duplicate of [What is a NullPointerException, and how do I fix it?](https://stackoverflow.com/questions/218384/what-is-a-nullpointerexception-and-how-do-i-fix-it) — Phantômaxx, Jun 06 '18 at 15:43

Michael Dodd · Accepted Answer · 2018-06-06T16:23:54.173

2

Your problem is the scope of db In onCreate():

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

    DatabaseHelper db = new DatabaseHelper(this);

    ...
}

You have this instance of db declared as a local variable, effectively creating two variables, both called db but operating at different scopes. This means that as soon as onCreate() is finished, this reference to db will be lost and garbage collected.

Your two instances of db are also of different types - SQLiteDatabase and DatabaseHelper, so a better variable naming strategy would help avoid problems like this in the future. As we'll be using the SQLiteDatabase version of db, we'll need to grab a writable instance of your database to use with the helper in future:

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

    db = new DatabaseHelper(this).getWritableDatabase();

    ...
}

This will ensure that you're setting the member variable rather than a local variable.

edited Jun 06 '18 at 16:23

answered Jun 06 '18 at 15:50

Michael Dodd

10,102
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Thank you for your reply, but if I do that I get this error: Incompatible types. Required: android.database.sqlite.SQLiteDatabase Found: com.example.w4e74.farmanimalfinal.DatabaseHelper – George Smith Jun 06 '18 at 15:56
Could you post the new error message as an [edit to your question](https://stackoverflow.com/posts/50724427/edit) rather than as a comment? – Michael Dodd Jun 06 '18 at 15:58
The field type is **SQLiteDatabase** he need to use **new DatabaseHelper(this).getWritableDatabase()** which returns **SQLiteDatabase** – Arpan Sarkar Jun 06 '18 at 15:59
@Arpan Cheers, will update my answer. Sorry for missing that, it's been a long day! – Michael Dodd Jun 06 '18 at 16:00
@GeorgeSmith Arpan's comment will fix that other issue. – Michael Dodd Jun 06 '18 at 16:06
I really appreciate your help, though I am now getting the error "Cannot resolve method 'getWriteableDatabase()" – George Smith Jun 06 '18 at 16:20
Sorry, that was a typo. Drop the first 'e' - it should be `getWritableDatabase()` – Michael Dodd Jun 06 '18 at 16:23
@GeorgeSmith No worries, if this answer has helped then please accept it by clicking the ✔icon below the score on the left. – Michael Dodd Jun 06 '18 at 16:28

Nullpointerexception when trying to insert a value into SQLite

1 Answers1