Transferring data between classes and forms

Question

long time reader, first time poster:

I've been trying to pick up C# and writing a game program, but am hung up on how to transfer data to my GUI from logic classes and visa-versa. Transferring strings would be ideal, and it seems pretty simple, so I was hoping someone could help me out.

In the most basic case, I'd like to know why this isnt working:

namespace MyGame
{
    public partial class GameWindow : Form
    {
        public LogicClass gameLogic;
        public GameWindow()
        {
            InitializeComponent();
        }
    private void startButton_Click(object sender, EventArgs e)
    {
        string toDisplay = gameLogic.getString();
        this.label1.Text = toDisplay;
    }
}

and the game logic class

namespace MyGame
{
    public class LogicClass
    {
        public string getString()
        {
            return "success!";
        }
    }
}

I've tried for a few days now to find out why I get a nullReferenceException at line

string toDisplay = gameLogic.getString();

this isn't the end result of what I'd like to do, of course, but if somebody could explain to me what's going on here and how I could pass a string from a different class to the GUI I think I'll be able to get a foothold into how to do the rest of the things that I'd like. I've seen a lot of things on transferring data from forms to other forms, but I can't find what I need about classes to forms. I know it can be done; its just too simple not to be possible. Can anyone help me out?

Thanks! Jake

Answer 1

Your data transfer logic is fine, the reason for the exception is gameLogic is never instantiated. You could replace public LogicClass gameLogic; with public LogicClass gameLogic = new LogicClass();

Or add gameLogic = new LogicClass(); in the constructor after the call to InitializeComponent().