NullPointerException when trying to delete a row

Question

getting Attempt to invoke virtual method int android.database.sqlite.SQLiteDatabase.delete(java.lang.String, java.lang.String, java.lang.String[]) on a null object reference

Since my code is very long, parts that have nothing to do with the issue at hand have been removed (they work just fine and have nothing to do with the database)

This is my code:

protected static final String ACTIVITY_NAME = "ChatWindow";
ListView myDisplay;
EditText myChat;
Button mySend;
ArrayList<String> myList;
ChatAdapter messageAdapter;
public static Cursor cursor;
SQLiteDatabase db;
Boolean isTablet;
FrameLayout fLayout;
ChatDatabaseHelper cdh;


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

    //declarations
    myDisplay = (ListView) findViewById(R.id.display);
    myChat = (EditText) findViewById(R.id.chat);
    mySend = (Button) findViewById(R.id.sndBtn);
    myList = new ArrayList<>();
    //in this case, “this” is the ChatWindow, which is-A Context object

    messageAdapter =new ChatAdapter( this );
    myDisplay.setAdapter (messageAdapter);

    cdh = new ChatDatabaseHelper(this);
    db = cdh.getWritableDatabase();

    cursor = db.rawQuery("SELECT * from ChatDatabaseHelper", null);

    cursor.moveToFirst();
    while(!cursor.isAfterLast() ){
        myList.add(cursor.getString(cursor.getColumnIndex(ChatDatabaseHelper.KEY_MESSAGE)));
        Log.i(ACTIVITY_NAME, "SQL MESASAGE:" + cursor.getString(
                cursor.getColumnIndex(ChatDatabaseHelper.KEY_MESSAGE)));
        Log.i(ACTIVITY_NAME, "Cursor's column count =" + cursor.getColumnCount() );
        cursor.moveToNext();


    //send button actions
    mySend.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            String message;
            message = myChat.getText().toString();
            myList.add(message);
            messageAdapter.notifyDataSetChanged(); //this restarts the   process of getCount()/getView()
            myChat.setText("");

            ContentValues cValues = new ContentValues();
            cValues.put(ChatDatabaseHelper.KEY_MESSAGE, message);
            db.insert(TABLE_NAME, "NullColumnName", cValues);

        }
    });

//This is where I need help
public void deleteEntry (String id) {

    Log.i("deleteRow", id);
//The log prints just fine so this method is being run and I have the correct value for id

    db.delete(ChatDatabaseHelper.TABLE_NAME, ChatDatabaseHelper.KEY_ID + "=" + id, null);
}

//You can ignore anything below
private class ChatAdapter extends ArrayAdapter<String> {
    public ChatAdapter(Context ctx) {
        super(ctx, 0);
    }
    @Override
    public int getCount() {
        return myList.size();
    }
    @Override
    public String getItem(int position) {
        return myList.get(position);
    }
    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        LayoutInflater inflater = ChatWindow.this.getLayoutInflater();
        View result = null ;
        if(position%2 == 0)
            result = inflater.inflate(R.layout.chat_row_incoming, null);
        else
            result = inflater.inflate(R.layout.chat_row_outgoing, null);

        TextView message = (TextView)result.findViewById(R.id.message_text);
        message.setText(   getItem(position)  ); // get the string at position
        return result;
    }
    public long getId(int position) {

        return Long.parseLong(myList.get(position));
    }
    public long getItemId(int position) {

        cursor.moveToPosition(position);
        return cursor.getInt(cursor.getColumnIndex(ChatDatabaseHelper.KEY_ID));
    }
}

protected void onDestroy() {
    super.onDestroy();
    cursor.close();
    db.close();
}

Below is the code for the database Activity:

public class ChatDatabaseHelper extends SQLiteOpenHelper {
    private static int VERSION_NUM = 1;
    private static String DATABASE_NAME = "Messages.db";
    final static String TABLE_NAME = "ChatDatabaseHelper";
    final static String KEY_ID = "id";
    final static String KEY_MESSAGE = "MESSAGE";

    private static final String CREATE_TABLE = "CREATE TABLE " + TABLE_NAME + "( "
            + KEY_ID + " INTEGER PRIMARY KEY AUTOINCREMENT, "
            + KEY_MESSAGE + " text "
            + " ); ";

    public ChatDatabaseHelper(Context ctx) {
        super(ctx, DATABASE_NAME, null, VERSION_NUM);
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        db.execSQL(CREATE_TABLE);
        Log.i("ChatDatabaseHelper", "Calling onCreate");
    }

    public void onUpgrade(SQLiteDatabase db) {
        db.execSQL("DROP TABLE IF EXISTS '" + TABLE_NAME + "'");
        onCreate(db);
    }

    public void onUpgrade(SQLiteDatabase db, int oldVer, int newVer) {
        Log.i("ChatDatabaseHelper", "Calling onUpgrade, oldVersion=" + oldVer + " newVersion=" + newVer);
        db.execSQL("DROP TABLE IF EXISTS '" + TABLE_NAME + "'");
        onCreate(db);
    }
}

Here is my stack trace:

   E/AndroidRuntime: FATAL EXCEPTION: main
              Process: com.example.himanshu.androidlabs, PID: 22613
              java.lang.NullPointerException: Attempt to invoke virtual method 'int android.database.sqlite.SQLiteDatabase.delete(java.lang.String, java.lang.String, java.lang.String[])' on a null object reference
                  at com.example.himanshu.androidlabs.ChatWindow.deleteEntry(ChatWindow.java:159)
                  at com.example.himanshu.androidlabs.MessageFragment$1.onClick(MessageFragment.java:55)
                  at android.view.View.performClick(View.java:6256)
                  at android.view.View$PerformClick.run(View.java:24701)
                  at android.os.Handler.handleCallback(Handler.java:789)
                  at android.os.Handler.dispatchMessage(Handler.java:98)
                  at android.os.Looper.loop(Looper.java:164)
                  at android.app.ActivityThread.main(ActivityThread.java:6541)
                  at java.lang.reflect.Method.invoke(Native Method)
                  at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:240)
                  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:767)

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) — Tripp Kinetics, Apr 16 '18 at 16:09

NullPointerException when trying to delete a row

0 Answers0