title: How add items(Text & Value) to ComboBox & read them in SelectedIndexChanged (SelectedValue = null)
body: <p>I want to add some items to a combobox like this :   </p>
  
  <pre><code>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);
  ...   
  </code></pre>
  
  <p>and read those texts and values in <code>SelectedIndexChanged</code> like this :   </p>
  
  <pre><code>private void ComboBox_Servers_SelectedIndexChanged(object sender, EventArgs e)
  {
      MessageBox.Show(ComboBox_Servers.SelectedValue.ToString());
  }
  </code></pre>
  
  <p>But SelectedValue is always null! what is the problem and how can I fix it?</p>