C# 通过组合框使用 SelectedIndexChanged 更改带有文本文件中文本的标签

Question

在组合框中，我可以将所有转换加载到组合框中。但是，当我从组合框中单击一个转换时，由于某种原因它会将数据更改为 null。我不确定是否有人可以在不查看我所有代码的情况下帮助我。但我认为值得一试。我正在尝试选择一个转换，即英尺到英里，并将“英尺”放在第一个标签中，将“英里”放在第二个标签中。下面是组合框点击事件的代码:

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

我不确定这是否是您想要的，但它是一种更简单的方法，可为您提供相同的功能。我认为如果将组合框绑定(bind)到转化列表，会简单得多。 selecteditem 和 selectedvalue 将更易于使用。

    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;
        }
    }
}