[c#] How add items(Text & Value) to ComboBox & read them in SelectedIndexChanged (SelectedValue = null)

I want to add some items to a combobox like this :

public class ComboboxItem
{
    public string Text { get; set; }
    public object Value { get; set; }

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

ComboboxItem item = new ComboboxItem();
item.Text = "choose a server...";
item.Value = "-1";
ComboBox_Servers.Items.Add(item);
...   

and read those texts and values in SelectedIndexChanged like this :

private void ComboBox_Servers_SelectedIndexChanged(object sender, EventArgs e)
{
    MessageBox.Show(ComboBox_Servers.SelectedValue.ToString());
}

But SelectedValue is always null! what is the problem and how can I fix it?

try this:

ComboBox cbx = new ComboBox();
cbx.DisplayMember = "Text";
cbx.ValueMember = "Value";

EDIT (a little explanation, sory, I also didn't notice your combobox wasn't bound, I blame the lack of caffeine):

The difference between SelectedValue and SelectedItem are explained pretty well here: ComboBox SelectedItem vs SelectedValue

So, if your combobox is not bound to datasource, DisplayMember and ValueMember doesn't do anything, and SelectedValue will always be null, SelectedValueChanged won't be called. So either bind your combobox:

            comboBox1.DisplayMember = "Text";
            comboBox1.ValueMember = "Value";

            List<ComboboxItem> list = new List<ComboboxItem>();

            ComboboxItem item = new ComboboxItem();
            item.Text = "choose a server...";
            item.Value = "-1";
            list.Add(item);

            item = new ComboboxItem();
            item.Text = "S1";
            item.Value = "1";
            list.Add(item);

            item = new ComboboxItem();
            item.Text = "S2";
            item.Value = "2";
            list.Add(item);

            cbx.DataSource = list; // bind combobox to a datasource

or use SelectedItem property:

if (cbx.SelectedItem != null)
             Console.WriteLine("ITEM: "+comboBox1.SelectedItem.ToString());

Dictionary<int,string> comboSource = new Dictionary<int,string>();
comboSource.Add(1, "Sunday");
comboSource.Add(2, "Monday");

Aftr adding values to Dictionary, use this as combobox datasource:

comboBox1.DataSource = new BindingSource(comboSource, null);
comboBox1.DisplayMember = "Value";
comboBox1.ValueMember = "Key";

This is similar to some of the other answers, but is compact and avoids the conversion to dictionary if you already have a list.

Given a ComboBox "combobox" on a windows form and a class SomeClass with the string type property Name,

List<SomeClass> list = new List<SomeClass>();

combobox.DisplayMember = "Name";
combobox.DataSource = list;

Which means that combobox.SelectedItem is a SomeClass object from list, and each item in combobox will be displayed using its property Name.

You can read the selected item using

SomeClass someClass = (SomeClass)combobox.SelectedItem;

        combo1.DisplayMember = "Text";
        combo1.ValueMember = "Value";   
        combo1.Items.Add(new { Text = "someText"), Value = "someValue") });
        dynamic item = combo1.Items[combo1.SelectedIndex];
        var itemValue = item.Value;
        var itemText = item.Text;

Unfortunatly "combo1.SelectedValue" does not work, i did not want to bind my combobox with any source, so i came up with this solution. Maybe it will help someone.