C# 4 and .NET 4

1230 ❘ ChaPTer 41 Asp.net feAtures
Multiple UpdatePanel Controls on a Single Web Page
You can include any number of UpdatePanel controls on a page. If a postback is caused by a control that
is contained in the of any UpdatePanel on the page, a partial-page postback will
occur instead of a full-page postback. This will cause all the UpdatePanel controls to update according to
the value of their UpdateMode property. The default value of this property is Always, which means that the
UpdatePanel will update for a partial-page postback operation on the page, even if this operation occurs
in a different UpdatePanel control. If you set this property to Conditional, the UpdatePanel updates
only when a control that it contains causes a partial-page postback or when a trigger that you have defined
occurs. Triggers are covered shortly.
If you have set UpdateMode to Conditional, you can also set the ChildrenAsTriggers property to
false to prevent controls that are contained by the UpdatePanel from triggering an update of the panel.
Note, though, that in this case these controls still trigger a partial-page update, which may result in other
UpdatePanel controls on the page being updated. For example, this will update controls that have an
UpdateMode property value of Always. This is illustrated in the following code:
Panel 1 render time:
Panel 2 render time:
Page render time:
In this code, the UpdatePanel2 control has an UpdateMode property of Always; the default value. When the
button is clicked, it will cause a partial-page postback, but only UpdatePanel2 will be updated. Visually,
you will notice that only the “Panel 2 render time” label is updated.
Server-Side UpdatePanel Updates
Sometimes when you have multiple UpdatePanel controls on a page, you might decide not to update one
of them unless certain conditions are met. In this case, you would configure the UpdateMode property of
the panel to Conditional as shown in the previous section and possibly also set the ChildrenAsTriggers
property to false. Then, in your server-side event-handler code for one of the controls on the page that
causes a partial-page update, you would (conditionally) call the Update() method of the UpdatePanel.
For example:
protected void Button1_Click(object sender, EventArgs e)
{
if (TestSomeCondition())
{
UpdatePanel1.Update();
}
}
UpdatePanel Triggers
You can cause an UpdatePanel control to be updated by a control elsewhere on the web page by adding
triggers to the Triggers property of the control. A trigger is an association between an event of a control
elsewhere on the page and the UpdatePanel control. All controls have default events (for example, the
default event of a Button control is Click), so specifying the name of an event is optional. There are two
types of triggers that you can add, represented by the following two classes:
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