When there is no item in RadComboBox i did't want check all option.
<
telerik:RadComboBox
ID
=
"RadComboBoxSites"
runat
=
"server"
OnClientItemChecking
=
"OnClientItemChecking"
CheckBoxes
=
"true"
EnableCheckAllItemsCheckBox
=
"true"
DataTextField
=
"SiteName"
DataValueField
=
"SiteUid"
AppendDataBoundItems
=
"true"
OnItemDataBound
=
"RadComboBoxSites_ItemDataBound"
DropDownWidth
=
"250px"
OnClientDropDownOpening
=
"disableComboBoxSeparator;disableCheckall"
EmptyMessage
=
"Please select a site..."
MaxHeight
=
"192px"
>
</
telerik:RadComboBox
>