SQLite error in onCreate

Question

iem following a tutorial on youtube about using SQLite in android and the code crashes the app on start code

MainActivity.java

package com.example.asd;

import android.app.Activity;
import android.database.sqlite.SQLiteDatabase;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;

public class MainActivity extends Activity {

VivzHelper vivzHelper;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    vivzHelper = new VivzHelper(this);
    SQLiteDatabase sqLiteDatabase = vivzHelper.getWritableDatabase();
}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.main, menu);
    return true;
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    // Handle action bar item clicks here. The action bar will
    // automatically handle clicks on the Home/Up button, so long
    // as you specify a parent activity in AndroidManifest.xml.
    int id = item.getItemId();
    if (id == R.id.action_settings) {
        return true;
    }
    return super.onOptionsItemSelected(item);
}
}

Message.java

package com.example.asd;

import android.content.Context;
import android.widget.Toast;

public class Message {

public static void message(Context context, String message) {
    Toast.makeText(context, message, Toast.LENGTH_LONG).show();
}
}

VivzHelper.java

package com.example.asd;

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

public class VivzHelper extends SQLiteOpenHelper {

private static final String DATABASE_NAME = "vivzdatabase";
private static final String TABLE_NAME = "VIVZTABLE";
private static final int DATABASE_VERSION = 1;
private static final String UID = "_id";
private static final String NAME = "Name";
private static final String CREATE_TABLE = "CREATE TABLE " + TABLE_NAME + " (" + UID
        + " INTEGER PRIMARY KEY  AUTOINCREMENT, " + NAME + " VARCHAR(255));";
private static final String DROP_TABLE = "DROP TABLE IF EXISTS" + TABLE_NAME;
private Context context;

public VivzHelper(Context context) {
    super(context, DATABASE_NAME, null, DATABASE_VERSION);
    Message.message(context, "constructor called");
}

@Override
public void onCreate(SQLiteDatabase db) {
    try {
        db.execSQL(CREATE_TABLE);
        Message.message(context, "onCreate called");
    } catch (SQLException e) {
        Message.message(context, "" + e);
    }
}

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

    try {
        Message.message(context, "onUpgrade called");
        db.execSQL(DROP_TABLE);
        onCreate(db);
    } catch (SQLException e) {
        Message.message(context, "" + e);
    }
}
}

The app crashes on

SQLiteDatabase sqLiteDatabase = vivzHelper.getWritableDatabase();

error log

12-11 19:49:16.459: E/AndroidRuntime(6043): FATAL EXCEPTION: main
12-11 19:49:16.459: E/AndroidRuntime(6043): Process: com.example.asd, PID: 6043
12-11 19:49:16.459: E/AndroidRuntime(6043): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.asd/com.example.asd.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.res.Resources android.content.Context.getResources()' on a null object reference
12-11 19:49:16.459: E/AndroidRuntime(6043):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2695)
12-11 19:49:16.459: E/AndroidRuntime(6043):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2769)
12-11 19:49:16.459: E/AndroidRuntime(6043):     at android.app.ActivityThread.access$900(ActivityThread.java:177)
12-11 19:49:16.459: E/AndroidRuntime(6043):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1430)
12-11 19:49:16.459: E/AndroidRuntime(6043):     at android.os.Handler.dispatchMessage(Handler.java:102)
12-11 19:49:16.459: E/AndroidRuntime(6043):     at android.os.Looper.loop(Looper.java:135)
12-11 19:49:16.459: E/AndroidRuntime(6043):     at android.app.ActivityThread.main(ActivityThread.java:5910)
12-11 19:49:16.459: E/AndroidRuntime(6043):     at java.lang.reflect.Method.invoke(Native Method)
12-11 19:49:16.459: E/AndroidRuntime(6043):     at java.lang.reflect.Method.invoke(Method.java:372)
12-11 19:49:16.459: E/AndroidRuntime(6043):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1405)
12-11 19:49:16.459: E/AndroidRuntime(6043):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1200)
12-11 19:49:16.459: E/AndroidRuntime(6043): Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.res.Resources android.content.Context.getResources()' on a null object reference
12-11 19:49:16.459: E/AndroidRuntime(6043):     at android.widget.Toast.<init>(Toast.java:130)
12-11 19:49:16.459: E/AndroidRuntime(6043):     at android.widget.Toast.makeText(Toast.java:427)
12-11 19:49:16.459: E/AndroidRuntime(6043):     at com.example.asd.Message.message(Message.java:9)
12-11 19:49:16.459: E/AndroidRuntime(6043):     at com.example.asd.VivzHelper.onCreate(VivzHelper.java:29)
12-11 19:49:16.459: E/AndroidRuntime(6043):     at android.database.sqlite.SQLiteOpenHelper.getDatabaseLocked(SQLiteOpenHelper.java:251)
12-11 19:49:16.459: E/AndroidRuntime(6043):     at android.database.sqlite.SQLiteOpenHelper.getWritableDatabase(SQLiteOpenHelper.java:163)
12-11 19:49:16.459: E/AndroidRuntime(6043):     at com.example.asd.MainActivity.onCreate(MainActivity.java:18)
12-11 19:49:16.459: E/AndroidRuntime(6043):     at android.app.Activity.performCreate(Activity.java:6178)
12-11 19:49:16.459: E/AndroidRuntime(6043):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1118)
12-11 19:49:16.459: E/AndroidRuntime(6043):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2648)
12-11 19:49:16.459: E/AndroidRuntime(6043):     ... 10 more

I do not know whats wrong with the code it looks exactly the same as in video ???

Answer 1

What is the problem?

getWritableDatabase calls your onCreate()

The first time this is called, the database will be opened and onCreate(SQLiteDatabase), onUpgrade(SQLiteDatabase, int, int) and/or onOpen(SQLiteDatabase) will be called.

in onCreate() you have

Message.message(context, "onCreate called");

context, at this point, is null because it is declared as a member variable at the top as

private Context context;

but it is never initialized. You pass the Context from your Activity to the db helper class constructor. Initializing the member variable, context, there gives that variable a value when you pass it to your message() function, hence getting rid of the NPE.

How did we get here?

Your stacktrace shows

Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 
'android.content.res.Resources android.content.Context.getResources()' 
on a null object reference

So you are trying to use a Context object to "do something" which, in this case, is to create and show a Toast object. Because if we look just a little further up in the stacktrace to the first line which references your project we find

at com.example.asd.Message.message(Message.java:9)

which is this line

Toast.makeText(context, message, Toast.LENGTH_LONG).show();

what could cause a problem here with the given stacktrace? Yes, context being null.

Which takes us back to

The app crashes on SQLiteDatabase sqLiteDatabase = vivzHelper.getWritableDatabase();

as you stated in your post. It crashes there, not because something in that line is explicitly wrong, but because something in that line calls something else that is crying for help.