We have a ComboBox with checkboxes that is populated in the server-side. Also there it is determined which items should be checked. AutoPostBack for the component is set to false and we trigger a postback through other means.
When the dropdown is closed (OnClientDropDownClosing or OnClientDropDownClosed event), we need to retain the items that were checked at the last postback.
Here is an example:
Let's say we have the items a,b,c,d in the ComboBox:
a and b are set to checked at the last postback. On the client-side the user makes some changes so that yet c and d are checked. Now he decides to close the dropdown. We want that yet a and b are left checked.
Currently we have that implemented through a "hack", but we have some cases with massive thata(2000 items+) where it takes several seconds before the dropdown closes, and this is a major performance issue. So is there any way to implement that behaviour?