title: OnItemSelectedIndexChange hide or remove selected DropDownList item
body: <p>I am sure this has been done but cannot seem to find a resolution anywhere, or figure it out at this late hour.</p>
  
  <p>I have two DropDownLists:</p>
  
  <p><code>ddConvertFrom</code>
  <code>ddConvertTo</code></p>
  
  <p><code>OnItemSelectedIndexChange</code> for either of the DropDownLists, I want to remove/hide the selected value from the other DropDownList.</p>
  
  <p>So far I have tried this:</p>
  
  <pre><code>protected void ddConvertTo_SelectedIndexChanged(object sender, EventArgs e)
  {
      foreach (ListItem li in ddConvertTo.Items)
      {
          if (ddConvertFrom.SelectedItem.Text == li.Text)
          {
              ddConvertTo.Items.Remove(ddConvertTo.Items.FindByValue(ddConvertFrom.SelectedItem.Text));
          }
  
      }
  }
  </code></pre>
  
  <p>A) Why does the above not work?</p>
  
  <p>B) Is there a more efficient way of doing this above?</p>