Comparing DropDownLists - asp.net-4.0

Question

I'm having a page that contains several dropdownlists, all filled with the same values. I would like to compare them on the client as well as on the server side.
The problem is though, that the dropdownlists are generated dynamically because their quantity can vary.

Answer 1

Client side comparing:
<script type="text/javascript">
function CompareSelectedValues(dropDown1ID, dropDown2ID) {
var DropDownList1 = document.getElementById(dropDown1ID);
var DropDownList2 = document.getElementById(dropDown2ID);
if (DropDownList1.selectedIndex != -1 && DropDownList2.selectedIndex != -1) {
if (DropDownList1.options[DropDownList1.selectedIndex].value != DropDownList2.options[DropDownList2.selectedIndex].value)
alert('not same');
}
}
</script>
Classic server side comparing with C#:
private bool AreDropDownListValuesEqual(DropDownList ddlist1, DropDownList ddlist2)
{
// Check for invalid input or different number of items for early return
if (ddlist1 == null || ddlist2 == null || ddlist1.Items.Count != ddlist2.Items.Count)
{
return false;
}
// Check items one by one. We need a nested loop because the list could be sorted differently while having the same values!
foreach (ListItem outerItem in ddlist1.Items)
{
bool hasMatch = false;
foreach (ListItem innerItem in ddlist2.Items)
{
if (innerItem.Value == outerItem.Value && innerItem.Text == outerItem.Text)
{
hasMatch = true;
break;
}
}
if (!hasMatch)
{
return false;
}
}
// All items from ddlist1 had a match in ddlist2 and we know that the number of items is equal, so the 2 dropdownlist are matching!
return true;
}

Answer 2

What kind of comparison do you need? If you don't keep them in a List and that list in Session, you can never do anything with them since you add them dynamically. Add your dropdownlists where you create them (this should me when Page.IsPostBack == false) and keep that list in session. On postbacks, load your dropdowns from the list. You can compare them using the list you keep.