I might be going about this in totally the wrong way but this is what I'm doing:
I have 2 custom web parts: a company calendar and an appointment list. Both are visual webparts and both contain an UpdatePanel control. The calendar provides a date and the appointment list consumes a date. When the selected date in the calendar part changes the appointment list is notified. The UpdatePanel is intended to prevent the whole page from being refreshed.
This works fine when the page is loaded. However, when the calendar date is changed, a postback is raised. The appointment part is refreshed but the provider link is null. (i.e. the connection is not explicitly reinitialised) Therefore it is not possible to fetch the date from the provider (Calendar).
I tried to save the provider in the ViewState but I get an error saying that the calendar part is not marked as serialisable. At this point I start to wonder if I'm doing this wrong :-/
How should this be done?