NullReferenceException

Unity Engine
1

I need some help. I’m writing a C# script (I’m new to the world of C#) and I’m getting the following error after I begin running my Scene:

Line 28 is:

SQLdb.Start();

What I am trying to do is access a mySQL database. Store the results in some type of object that I can return to a second script, which will populate the resulting data into a TreeView control.

Here’s my code: AddClass.cs

void Start () 
	{
		// Setup the TreeView to retrieve Database data.
		m_myTreeView = gameObject.GetComponent<TreeViewControl>();
		if (null == m_myTreeView)
		{
			Debug.LogError("Use the tree view menu to add the control");
			return;
		}
		//	TreeViewItem item1 = item.RootItem.AddItem("Playable Races and Classes");
		
		// Setup the Database functions.
		SQLdb = gameObject.GetComponent<SQLDatabase>();
				
		// Open a database connection and retrieve the data for Classes.
		SQLdb.Start();
		PopulateTreeData();
	}

SQLDatabase.cs

using UnityEngine;
using System;
using System.Collections;
using System.Data;
using MySql.Data.MySqlClient;

public class SQLDatabase : MonoBehaviour {
    // Global variables
    private static IDbConnection dbConnection;
    
    // Initialisation
    public void Start() {
        openSqlConnection();
    }
    
    // On quit
    public void OnApplicationQuit() {
        closeSqlConnection();
    }
    
    // Connect to database
    private static void openSqlConnection() {
... Omitted for security ... 
}

// Disconnect from database
    private static void closeSqlConnection() {
        dbConnection.Close();
        dbConnection = null;
        Debug.Log("Disconnected from database.");
    }

// MySQL Query
    public static ArrayList doQuery(string sqlQuery) {
        IDbCommand dbCommand = dbConnection.CreateCommand();
        dbCommand.CommandText = sqlQuery;
        // IDataReader reader = dbCommand.ExecuteReader();
		ArrayList rowList = new ArrayList();
		IDataReader reader = dbCommand.ExecuteReader();
		while (reader.Read())
		{
			object[] values = new object[reader.FieldCount];
			reader.GetValues(values);
			rowList.Add(values);
		}
        reader.Close();
        reader = null;
        dbCommand.Dispose();
        dbCommand = null;
		return rowList;
    }

I would really appreciate any help you all could provide. Thank you!

2

Run the debugger, SQLdb is likely null.

3

Dumb question: How do I run the debugger?

4

Through MonoDevelop. Knowing your tools is critical for self-help, it will also save time.