RadListBox - at least have one item

[Mar]

Hello,

I am building a page similar to the following:
http://demos.telerik.com/aspnet-ajax/listbox/examples/applicationscenarios/insertitem/defaultcs.aspx

One of the requirements is that as part of the validation, I have to check that at least one item is present inside the RadListBox.  I tried using the RequiredFieldValidator but that enforces the validation that the item in the listbox should be selected.

In my case, I just want to check that the listbox has at least one item.  (I don't want my users to select one item for this validation to succeed).  How can I accomplish this that the validation succeeds if the listbox has one item which may or may not be selected?

Thanks,
Pratik

[Veselin Vasilev]

Hi Pratik,

In your case you need to use a CustomValidator. In its client validation function you can find the listbox and check the number of its items. Here is an example:

<script type="text/javascript">
function validateListbox(source, args)
{
   var list = $find("<%= RadListBox1.ClientID %>");
   args.IsValid = list.get_items().get_count() > 0;
}
</script>

Best wishes,
Veselin Vasilev
the Telerik team

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[Todd]

How do I do this when my RadListBox is within a FormView's EditItemTemplate?

[Genady Sergeev]

Hello Todd,

You can try the following, in the ItemCommand event of FormView use the following code:

protected void FormView1_ItemCommand(object sender, FormViewCommandEventArgs e)
{

    if (e.CommandName == "Update")
    {
        var listBox = (sender as FormView).FindControl("RadListBox") as RadListBox;
        ClientScript.RegisterClientScriptBlock(typeof(Page), "listbox", string.Format("window['listbox']={0}", listBox.ClientID));
    }
}

Then use window['listbox'] to obtain the id of the listbox:

function validateListbox(source, args)
{
   var list = $find("windod['listbox']");
   args.IsValid = list.get_items().get_count() > 0;
}

Regards,
Genady Sergeev
the Telerik team