UpdatePanel Triggers
The update panel was changed since the last beta and CTP versions. Before it didn't contain some of the postback triggers that were available. So I experimented with the new features, and it's pretty cool how the final version works. For instance, if you have a control outside of the update panel:
<asp:DropDownList id="ddlMake" runat="server" AutoPostBack="true" .. />
You can refresh the second list whenever an item in the first list changes by "hooking" up to the first drop down through an AsyncPostBackTrigger, as such:
<asp:UpdatePanel id="upModel" runat="server" Mode="Conditional">
<ContentTemplate>
<asp:DropDownList id="ddlModel" runat="server" />
</ContentTemplate>
<Triggers>
<asp:AsyncPostBackTrigger ControlID="ddlMake" />
</Triggers>
</asp:UpdatePanel>
You can also hook up to a specific event through EventName as well. Now, what if you have a control in an update panel, that you don't want to work with the asynchronous updates? I actually had this happen. This is where the <asp:PostBackTrigger> comes in, because it can register a control that will post back, allowing you to work in the opposite direction, if so desired.