Inserting into SQLite database - Android

Question

I am trying to implement a SQLite database for a highscores table. I am just testing it to see if my database creation and insertion is working with the below code. But I am getting a NullPointerException on the below lines.

Thank you in advance!

Results.java

public class Results extends Activity {
    DatabaseHelper dh;

    public void onCreate(Bundle savedInstanceState) {
        dh = DatabaseHelper.getInstance(this);

    public void showResults() {
        dh.openDB();  
        dh.insert(1231423, 436346);  //Line 104
    }
}

DatabaseHelper.java

private static final String SCORE = "score"; 
private static final String PERCENTAGE = "percentage";
public static DatabaseHelper mSingleton = null;

public synchronized static DatabaseHelper getInstance(Context context) {
    if(mSingleton == null) {
        mSingleton = new DatabaseHelper(context.getApplicationContext());
    }
    return mSingleton;
}

public SQLiteDatabase openDB() {
    return this.getWritableDatabase();
}

public long insert(long score, int percentage) {
    ContentValues values = new ContentValues();
    values.put(SCORE, score);  
    values.put(PERCENTAGE, percentage); 

    return db.insert(TABLE, null, values);  //Line 91
}

LogCat output

01-02 17:56:47.609: E/AndroidRuntime(1322): FATAL EXCEPTION: main
01-02 17:56:47.609: E/AndroidRuntime(1322): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.test/com.example.test.Results}: java.lang.NullPointerException
01-02 17:56:47.609: E/AndroidRuntime(1322):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2059)
01-02 17:56:47.609: E/AndroidRuntime(1322):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2084)
01-02 17:56:47.609: E/AndroidRuntime(1322):     at android.app.ActivityThread.access$600(ActivityThread.java:130)
01-02 17:56:47.609: E/AndroidRuntime(1322):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1195)
01-02 17:56:47.609: E/AndroidRuntime(1322):     at android.os.Handler.dispatchMessage(Handler.java:99)
01-02 17:56:47.609: E/AndroidRuntime(1322):     at android.os.Looper.loop(Looper.java:137)
01-02 17:56:47.609: E/AndroidRuntime(1322):     at android.app.ActivityThread.main(ActivityThread.java:4745)
01-02 17:56:47.609: E/AndroidRuntime(1322):     at java.lang.reflect.Method.invokeNative(Native Method)
01-02 17:56:47.609: E/AndroidRuntime(1322):     at java.lang.reflect.Method.invoke(Method.java:511)
01-02 17:56:47.609: E/AndroidRuntime(1322):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786)
01-02 17:56:47.609: E/AndroidRuntime(1322):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
01-02 17:56:47.609: E/AndroidRuntime(1322):     at dalvik.system.NativeStart.main(Native Method)
01-02 17:56:47.609: E/AndroidRuntime(1322): Caused by: java.lang.NullPointerException
01-02 17:56:47.609: E/AndroidRuntime(1322):     at com.example.test.DatabaseHelper.insert(DatabaseHelper.java:91)
01-02 17:56:47.609: E/AndroidRuntime(1322):     at com.example.test.Results.showResults(Results.java:104)
01-02 17:56:47.609: E/AndroidRuntime(1322):     at com.example.test.Results.onCreate(Results.java:50)
01-02 17:56:47.609: E/AndroidRuntime(1322):     at android.app.Activity.performCreate(Activity.java:5008)
01-02 17:56:47.609: E/AndroidRuntime(1322):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1079)
01-02 17:56:47.609: E/AndroidRuntime(1322):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2023)
01-02 17:56:47.609: E/AndroidRuntime(1322):     ... 11 more

EDIT: The NullPointerException is at least jumping around but errors still are there. I have edited my code and posted the new LogCat output.

As the exception clearly states, the problem is at Results.showResults which I don't see anywhere in your post — K-ballo
– K-ballo, Commented Jan 2, 2013 at 22:33
@K-ballo the dh.insert() call is in the showResults() method in the class Results. Sorry for the confusion. I should have shown that in my code posted. — Matt
– Matt, Commented Jan 2, 2013 at 22:57
@StefandeBruijn I never initialized DatabaseHelper dh anywhere. Could that be a problem? — Matt
– Matt, Commented Jan 2, 2013 at 22:58

Sam · Accepted Answer · 2013-01-02 23:08:08Z

1

Change openDB() to save the SqliteDatabase it opens and open a writable database:

public void openDB() {
    db = this.getWritableDatabase();
}

But this still doesn't match your stack trace, however it matches the code you provided.

answered Jan 2, 2013 at 23:08

Sam

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3 Comments

Matt Over a year ago

I fixed what you suggested and the NPE went away. A NPE still exists just at a different spot now. I updated my opening post if you do not mind taking another look at it.

Sam Over a year ago

You are still using return this.getWritableDatabase(); change it too db = this.getWritableDatabase();.

Matt Over a year ago

Oh whoops, I thought I had it but apparently didn't. It works now! I now need to work on pulling back out what I inserted and displaying it to TextViews. Thanks again Sam.

ashokgelal · Accepted Answer · 2013-01-02 23:08:11Z

1

You said you are doing:

DatabaseHelper dh;

dh.insert(1231423, 436346);

Looks like you are not instantiating dh:

dh = new DatabaseHelper(this);

A better approach would be to use the singleton pattern as you are ever going to need just one DatabaseHelper instance:

private static final String TABLE_NAME = "table_name";
private static final int SCHEME_VERSION = 1;
public static DatabaseHelper mSingleton = null;

private DatabaseHelper(Context ctxt) {
    super(ctxt, DATABASE_NAME, null, SCHEME_VERSION);
}

public synchronized static DatabaseHelper getInstance(Context ctxt) {
    if (mSingleton == null)
        mSingleton = new DatabaseHelper(ctxt.getApplicationContext());
    return mSingleton;
}

Now you can call like so:

DatabaseHelper dh = DatabaseHelper.getInstance(this);

answered Jan 2, 2013 at 23:08

ashokgelal

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1 Comment

Matt Over a year ago

The NPE is jumping around after implementing everything you had above. I edited my opening post and the new code, errors and LogCat.

fedepaol · Accepted Answer · 2013-01-02 22:36:23Z

0

If you are following the common SqlliteHelper pattern, you are likely to have forgotten to call the .open() method before calling insert.

answered Jan 2, 2013 at 22:36

fedepaol

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4 Comments

Matt Over a year ago

You are right, I did not call open(). Should that be added in as the first line of code in the insert() method?

fedepaol Over a year ago

A way to use it is to call open() in onResume() method and close() in onPause() methods of your activity.

Matt Over a year ago

I updated what @StefandeBruijn and you suggested and edited my opening post with errors commented into the code. I made the code a little more clearer too.

fedepaol Over a year ago

I think you should init db in your public SQLiteDatabase openDB() { return this.getReadableDatabase(); } , something like db = this.getReadableDatabase()

jojo · Accepted Answer · 2015-10-14 03:51:03Z

package com.example.hostelmangement;
import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteDatabase.CursorFactory;
import android.database.sqlite.SQLiteOpenHelper;

public class DataBaseHelper extends SQLiteOpenHelper {

public DataBaseHelper(Context context, String name, CursorFactory factory,
        int version)
{
    super(context, name, factory, version);
    // TODO Auto-generated constructor stub
}

@Override
public void onCreate(SQLiteDatabase db)
{
    db.execSQL("create table demo(id integer primary key,join_date date,name text,father_name text,date_of_birth text,house_name text,place text,pin_no text,blood_group text,mobile text,email text,company text,company_place text,company_phone text,company_pin,rent text,pending integer,status text,photo text,Proof text)");

}

@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) 
{
    // TODO Auto-generated method stub

}

}

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