Triggers are child tags for ‘UpdatePanel
’ tag. Many times we would like to update the panel when some event occurs or a value change on a control. This can be achieved by using triggers. There are two types of triggers ‘ControlEventTrigger
’ and ‘ControlValueTrigger
’. So let’s first understand ‘ControlEventTrigger
’. Using ‘ControlEventTrigger
’ we define on which control and at which event the update panel should refresh. Below is a simple code snippet for ‘ControlEventTrigger
’. ‘ControlEventTrigger
’ are defined using ‘<atlas:ControlEventTrigger>
’ tag. We have numbered the code snippet below so let’s understand the same with numbers:-
- 1 -> We need to define ‘
ControlEventTrigger
’ using ‘<atlas:ControlEventTrigger>
’ tag.
- 2 -> In this sample we will link trigger in ‘
UpdatePanel1
’ with the click event of ‘Button1
’.
- 3 -> In the ‘
<atlas:ControlEventTrigger>
’ tag we need to define the control and event using ‘ControlId
’ and ‘EventName
’ properties respectively.
So now when the button click event happens ‘UpdatePanel1
’ is refreshed.

Figure 18.12: - Code snippet for ‘ControlEventTrigger’
Using ‘ControlValueTrigger
’ we can update a panel when an external control has reached some value. So again we need to define the same in a ‘Triggers
’ tag. We need to put the ‘ControlvalueTrigger
’ tag with control and property defined using the ‘ControlId
’ property. So according to below code snippet when the value of ‘Textbox1
’ changes we need to update the top panel.

Figure 18.13:- ‘ControlValueTrigger’ code snippet
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