WinForms Custom ComboBox does not display names of List items

Question

I am trying to create a custom ComboBox in c# Winforms for using with custom Highlight color. Found some examples from the internet and modified a little to keep my codes clean.But there is something wrong that i can not fix so i need your help.

here my custom ComboBox class:

using System.Drawing;
using System.Windows.Forms;

namespace TesTApp
{
    class ThemedComboBox : ComboBox
    {
        protected Color _HighLightColor;       
        [System.ComponentModel.Description("High Light Color for selection"),
        System.ComponentModel.Category("HighLight"),
        System.ComponentModel.DefaultValue(typeof(Color), "Gray")]
        public Color HighlightColor
        {
            get { return _HighLightColor; }
            set
            {
                _HighLightColor = value;
                Invalidate();
                Update();
            }
        }

        public ThemedComboBox()
        {
            InitializeComponent();
        }

        private void InitializeComponent()
        {
            this.DrawMode = DrawMode.OwnerDrawFixed;
            HighlightColor = Color.FromArgb(255, 167, 36);
            this.DrawItem += new DrawItemEventHandler(ComboBox_DrawItem);            
        }
        void ComboBox_DrawItem(object sender, DrawItemEventArgs e)
        {
            if (e.Index < 0)
                return;

            if ((e.State & DrawItemState.Selected) == DrawItemState.Selected)
                e.Graphics.FillRectangle(new SolidBrush(HighlightColor),
                                         e.Bounds);
            else
                e.Graphics.FillRectangle(new SolidBrush(BackColor),
                                         e.Bounds);

            e.Graphics.DrawString(Items[e.Index].ToString(), e.Font,
                                  new SolidBrush(ForeColor),
                                  new Point(e.Bounds.X, e.Bounds.Y));

            e.DrawFocusRectangle();
        }
    }
}

When i call the method for fill the ComboBox with List , DropDown does not display the names of items.

At first i created a class to fill the data

  public class testItems
    {
        public string itemName { get; set; }
        public int itemValue { get; set; }
    }

And then i am calling the method that fills the ComboBox :

int maxItem = 5;
private void TestComboBox1()
{
   List _list = new List();
   for (int i = 0; i < maxItem; i++)
   {
     _list.Add(new testItems
      {
        itemName = "Item no: " + i.ToString(),
        itemValue = i
       });
   }
   themedComboBox1.DataSource = _list;
   themedComboBox1.DisplayMember = "itemName";
   themedComboBox1.ValueMember = "itemValue";
}

With this method , ComboBox DropDown does not display the name(DisplayMember) of items.

Then i have tried to fill ComboBox with a string array.With string array ComboBox displays the items but with this way i can not give values to items.

Here my method for fill the ComboBox with string array:

 int maxItem = 5;
 private void TestComboBox2()
 {
   string[] items = new string[maxItem];
   for (int i = 0; i < maxItem; i++)
   {
      items[i] = "Item No : " + i;
   }
   themedComboBox2.DataSource = items;
 }

All i want to have a custom ComboBox with custom Highlight color.Where am i doing wrong? Can you please help me to correct this?

user_3873323 · Answer

The values you see "TestTApp.testItems" are actually generated in the virtual method Object.ToString(). If your sole issue is replacing these values, you can override that ToString method for your testItems class (which, by the way, I'd recommend naming TestItem)

See this:

public class testItems
{
    public string itemName { get; set; }
    public int itemValue { get; set; }

    public override string ToString()
    {
        return itemName;
    }
}

Working with lists and Combo boxes (not limited to combo boxes) is fairly simple, you don't have to worry about row numbers and column names as you have to do with general data sources. In fact, you don't even need to set the DisplayMember and DataMember.

Just notice that when working with this kind of approach, you work with values of type testItems, and not actually the type which you desired ValueMember to hold. For instance, calling themedComboBox1.SelectedValue returns an testItems object (and not an int).

WinForms Custom ComboBox does not display names of List<> items

1 Answers