C# using SelectedIndexChanged via Combo Box to change a label with text from a text file

Question

In the combo box I can get it to load all the conversions to the combo box. But, when I click a conversion from the combo box it changes the data to null for some reason. I am not sure if anyone can help me without looking at all my code. But I thought it was worth a shot. I am trying to select a conversion I.e feet to miles and have the "feet" be in the first label and the "miles" be in the second. Here is the code for the click event of the combo box:

public void CmboBxConversion_SelectedIndexChanged(object sender, EventArgs e)
{
    //This is not working. If I were to say change the  conversion.From to "hello world" the label text does change to hello world.
    //But, as is it is it changes it to a null.
    Conversion conversion = new Conversion();

    Lbl1stConv.Text = conversion.From;  //these are labels
    LblSecondConv.Text = conversion.To;
}

//this is my Conversion class
public class Conversion
{
    public string From { get; set; }
    public string To { get; set; }
    public decimal Multiplier { get; set; }

    public string GetDisplayText(string sep)
    {
        return From + ("|") + To + ("|") + Multiplier;
    }

    public string GetCmboBxText(string sep)
    {
        return From + (" to ") + To;
    }
}

//this is how I am loading the combo box
private void Conversion_Load(object sender, EventArgs e)
{
    conversions = ConversionDB.GetConversions();
    FillConversionComboBox();
}

//here is the method used to fill the combobox
private void FillConversionComboBox()
{
    CmboBxConversion.Items.Clear();

    foreach (Conversion c in conversions)
    {
        CmboBxConversion.Items.Add(c.GetCmboBxText("\n"));
    }
}

    //this is a data base class that the textfile is pulling data
    public static class ConversionDB
{
    public const string Path = @"..\..\Conversions.txt";
    //public const string Path = Dir + "Conversions.txt";

    public static List<ConversionList> GetConversions()
    {


        StreamReader textIn = new StreamReader(
            new FileStream(Path, FileMode.Open, FileAccess.Read));
        List<ConversionList> conversions = new List<ConversionList>();
        while (textIn.Peek() != -1)
        {
            string row = textIn.ReadLine();
            string[] columns = row.Split('|');
            ConversionList conversion = new ConversionList();
            conversion.From = columns[0];
            conversion.To = columns[1];
            conversion.Multiplier = Convert.ToDecimal(columns[2]);
            conversions.Add(conversion);
        }

        textIn.Close();
        return conversions;
    }

Answer 1

I'm not sure if this is what you want but it is a little simpler approach that gives you the same functionality. I think it will be much simpler if you bind the combobox to your list of conversions. The selecteditem and selectedvalue will be easier to work with.

    public partial class Form1 : Form
{
    private List<Conversion> conversions=new List<Conversion>();
    public Form1()
    {
        InitializeComponent();
    }

    private void Form1_Load(object sender, EventArgs e)
    {
        loadconversions();
        //foreach (Conversion c in conversions)
        //{this.comboBox1.Items.Add(c); }
        comboBox1.DataSource = conversions;
        this.comboBox1.DisplayMember = "GetCmboBxText";

    }

    private void loadconversions()
    {
        fillconversions("feet","yards",3);
        fillconversions("yard", "feet", 0.33m);
        fillconversions("km", "mile", 0.54m);
        fillconversions("mile", "km", 1.6m);
        fillconversions("quarts", "gallons", 4);

    }
    private void fillconversions(string from, string to, decimal multiplier)
    {
        conversions.Add(new Conversion(from, to, multiplier));
    }

    private void comboBox1_SelectedIndexChanged(object sender, EventArgs e)
    {
        Conversion c = (Conversion)this.comboBox1.SelectedItem;
        this.textBox1.Text = c.GetDisplayText;
    }
}
public class Conversion
{
    public string From { get; set; }
    public string To { get; set; }
    public decimal Multiplier { get; set; }

    public Conversion(string from, string to, decimal multiplier)
    {
        From = from;
        To = to;
        Multiplier = multiplier;
    }

    public string GetDisplayText
    {
        get { return From + ("|") + To + ("|") + Multiplier; }
    }

    public string GetCmboBxText
    {
        get
        {
            return From + (" to ") + To;
        }
    }
}