Android getWritableDatabase() throws a NullPointerException

Question

I am having trouble with my call to getWritableDatabase(). It is returning a NullPointerException. The thing that is strangest is that this error only began occurring after I commented out a couple lines of code in my android manifest. Now the project is back to where it was (I un-commented those sections and it still throws a NullPointerException). So I checked my context and tried this.getBaseContext() and this.getApplicationContext().

Using getApplicationContext() puts this out to logcat:

08-12 09:24:20.042: E/AndroidRuntime(5572): FATAL EXCEPTION: main
08-12 09:24:20.042: E/AndroidRuntime(5572): java.lang.RuntimeException: Unable to instantiate service com.productivity.uptimeapp.NetService: java.lang.NullPointerException
08-12 09:24:20.042: E/AndroidRuntime(5572):     at android.app.ActivityThread.handleCreateService(ActivityThread.java:2395)
08-12 09:24:20.042: E/AndroidRuntime(5572):     at android.app.ActivityThread.access$1600(ActivityThread.java:139)
08-12 09:24:20.042: E/AndroidRuntime(5572):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1313)
08-12 09:24:20.042: E/AndroidRuntime(5572):     at android.os.Handler.dispatchMessage(Handler.java:99)
08-12 09:24:20.042: E/AndroidRuntime(5572):     at android.os.Looper.loop(Looper.java:137)
08-12 09:24:20.042: E/AndroidRuntime(5572):     at android.app.ActivityThread.main(ActivityThread.java:5021)
08-12 09:24:20.042: E/AndroidRuntime(5572):     at java.lang.reflect.Method.invokeNative(Native Method)
08-12 09:24:20.042: E/AndroidRuntime(5572):     at java.lang.reflect.Method.invoke(Method.java:511)
08-12 09:24:20.042: E/AndroidRuntime(5572):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:789)
08-12 09:24:20.042: E/AndroidRuntime(5572):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:556)
08-12 09:24:20.042: E/AndroidRuntime(5572):     at dalvik.system.NativeStart.main(Native Method)
08-12 09:24:20.042: E/AndroidRuntime(5572): Caused by: java.lang.NullPointerException
08-12 09:24:20.042: E/AndroidRuntime(5572):     at android.content.ContextWrapper.getApplicationContext(ContextWrapper.java:101)
08-12 09:24:20.042: E/AndroidRuntime(5572):     at com.productivity.uptimeapp.NetService.<init>(NetService.java:45)
08-12 09:24:20.042: E/AndroidRuntime(5572):     at java.lang.Class.newInstanceImpl(Native Method)
08-12 09:24:20.042: E/AndroidRuntime(5572):     at java.lang.Class.newInstance(Class.java:1319)
08-12 09:24:20.042: E/AndroidRuntime(5572):     at android.app.ActivityThread.handleCreateService(ActivityThread.java:2392)
08-12 09:24:20.042: E/AndroidRuntime(5572):     ... 10 more

Using getBaseContext() puts this out to logcat:

08-12 09:28:57.058: E/AndroidRuntime(5833): FATAL EXCEPTION: main
08-12 09:28:57.058: E/AndroidRuntime(5833): java.lang.RuntimeException: Unable to instantiate service com.productivity.uptimeapp.NetService: java.lang.NullPointerException
08-12 09:28:57.058: E/AndroidRuntime(5833):     at android.app.ActivityThread.handleCreateService(ActivityThread.java:2395)
08-12 09:28:57.058: E/AndroidRuntime(5833):     at android.app.ActivityThread.access$1600(ActivityThread.java:139)
08-12 09:28:57.058: E/AndroidRuntime(5833):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1313)
08-12 09:28:57.058: E/AndroidRuntime(5833):     at android.os.Handler.dispatchMessage(Handler.java:99)
08-12 09:28:57.058: E/AndroidRuntime(5833):     at android.os.Looper.loop(Looper.java:137)
08-12 09:28:57.058: E/AndroidRuntime(5833):     at android.app.ActivityThread.main(ActivityThread.java:5021)
08-12 09:28:57.058: E/AndroidRuntime(5833):     at java.lang.reflect.Method.invokeNative(Native Method)
08-12 09:28:57.058: E/AndroidRuntime(5833):     at java.lang.reflect.Method.invoke(Method.java:511)
08-12 09:28:57.058: E/AndroidRuntime(5833):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:789)
08-12 09:28:57.058: E/AndroidRuntime(5833):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:556)
08-12 09:28:57.058: E/AndroidRuntime(5833):     at dalvik.system.NativeStart.main(Native Method)
08-12 09:28:57.058: E/AndroidRuntime(5833): Caused by: java.lang.NullPointerException
08-12 09:28:57.058: E/AndroidRuntime(5833):     at android.database.sqlite.SQLiteOpenHelper.getDatabaseLocked(SQLiteOpenHelper.java:224)
08-12 09:28:57.058: E/AndroidRuntime(5833):     at android.database.sqlite.SQLiteOpenHelper.getWritableDatabase(SQLiteOpenHelper.java:164)
08-12 09:28:57.058: E/AndroidRuntime(5833):     at com.productivity.uptimeapp.NetService.<init>(NetService.java:46)
08-12 09:28:57.058: E/AndroidRuntime(5833):     at java.lang.Class.newInstanceImpl(Native Method)
08-12 09:28:57.058: E/AndroidRuntime(5833):     at java.lang.Class.newInstance(Class.java:1319)
08-12 09:28:57.058: E/AndroidRuntime(5833):     at android.app.ActivityThread.handleCreateService(ActivityThread.java:2392)
08-12 09:28:57.058: E/AndroidRuntime(5833):     ... 10 more

Here is my relevant NetService Code. It's called from my first Activity:

package com.productivity.uptimeapp;

import java.io.BufferedReader;
import java.io.DataOutputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.net.ServerSocket;
import java.net.Socket;
import java.net.SocketException;
import java.util.Iterator;

import org.json.JSONException;
import org.json.JSONObject;
import org.json.JSONTokener;

import android.app.Service;
import android.content.Intent;
import android.database.SQLException;
import android.database.sqlite.SQLiteDatabase;
import android.os.AsyncTask;
import android.os.Binder;
import android.os.IBinder;
import android.util.Log;

public class NetService extends Service{

    private static final String TAG = NetService.class.getSimpleName();

    //variables for ServerGet
    ServerSocket serverSocket;
    private static Socket clientSocket;
    //server port
    private static final int PORT = 8888;
    private static InputStreamReader isReader;
    private static DataOutputStream dos;
    private static PrintWriter printWriter;
    private static BufferedReader bReader;
    private String mess;
    //...end ServerGet variables

    ServerGet myFeed;
    Client out;

    DbHelper dbHelper = new DbHelper(this.getBaseContext()); 
    SQLiteDatabase db = dbHelper.getWritableDatabase();

    private final IBinder iBinder = new LocalBinder();

    public class LocalBinder extends Binder {
        public NetService getService() {
            // Return this instance of LocalService so clients can call public methods
            return NetService.this;
        }
    }

    @Override
    public IBinder onBind(Intent arg0) {
        //creates new AsyncTask
        myFeed = new ServerGet();
        //starts new AsyncTask
        myFeed.execute();

        return iBinder;

    }

    //ServerGet class asynchronously gets new strings
    private class ServerGet extends AsyncTask <Void, String, Integer>{
         //This contains my Server which gets messages from a client and responds accordingly   
    }
}

The lines that I commented out in my Manifest only served to get me to the default home screen so I could change some settings. Normally, I would want this app to replace HOME thus the android.intent.category.HOME attribute. I am doubtful that this is the problem but commenting out those three lines is what triggered it.

<application
        android:allowBackup="true"
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name"
        android:theme="@style/fullscreen">
        <service android:name="NetService" />
        <activity
            android:name="com.productivity.uptimeapp.Login"
            android:label="@string/app_name"
            android:screenOrientation="landscape" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <!-- <category android:name="android.intent.category.DEFAULT" /> -->
                <!-- <category android:name="android.intent.category.LAUNCHER" /> -->
                <!-- <category android:name="android.intent.category.HOME"/> -->            
            </intent-filter>
        </activity> 
        ...

The only reason I'm posting is because none of the other solutions I have found are working. I hope I'm just missing something simple... Thanks in advance!

EDIT: I have found a solution which was to instantiate db before I called it each time (passed as an argument in my AsyncTask methods). This is because I can not have dbHelper and db accessing the database at the same time. This was a no-brainer but now I have a bunch of instantiated db variables where I'd like to only have one near the top. Can I make that work?

Answer 1

com.productivity.uptimeapp.NetService.<init>(NetService.java:45)

This line in the logcat suggests there's a problem instantiating your class (<init>).

In the code, there's the following member variable initialization:

DbHelper dbHelper = new DbHelper(this.getBaseContext()); 
SQLiteDatabase db = dbHelper.getWritableDatabase();

The problem is there. You cannot use the class instance as Context until onCreate(). Defer your dbHelper and db initialization to onCreate() or later.