Process for Implementing Triggers and Timers

Process for Implementing Triggers and Timers

An UpdatePanel control on your page will update (through a partial-page postback operation) when a control that it contains causes a postback (for example, when you click a Button control in the ContentTemplate of the UpdatePanel control). You can also use triggers and timers to cause UpdatePanel controls to update in response to other events on the client.

Triggers

You can add a trigger specification to an UpdatePanel control to force it to update when a specified event occurs on the client.

Two types of trigger are available:

AsyncPostBackTrigger

This trigger links the UpdatePanel control to an event of a specified control. For example, you could trigger the update of the UpdatePanel when the OnClick event of a Button control is raised, or when the OnSelectedIndexChanged event occurs for a DropDownList control.

PostBackTrigger

This trigger works just like AsyncPostBackTrigger except that the targeted control will trigger a full-page postback instead of a partial-page postback. This is useful if you have a button in the of an UpdatePanel control that you want to refresh the whole page instead of just the contents of the UpdatePanel control.

To add a AsyncPostBackTrigger trigger to an UpdatePanel control:

 1. Add a control that has a property which, when you change it, should trigger an update of the UpdatePanel control.

 2. Add a Triggers child element to the UpdatePanel control.

 3. Add a AsyncPostBackTrigger child element to the UpdatePanel control.

 4. Add a ControlID attribute to the AsyncPostBackTrigger element. The value of this attribute is the ID of the control that triggers the update.

5. To use an event other than the default event for the targeted control, or to specify the event of the targeted control explicitly, add an EventName attribute to the AsyncPostBackTrigger element. The value of this attribute is the name of the event of the control that, when raised, triggers the update. For example, use Click for the OnClick property of a button.

Timers

By using a Timer server control you can cause an UpdatePanel control to update periodically, at an interval that you specify. To do this, you can either place the Timer control in the ContentTemplate of the UpdatePanel control, or place it elsewhere on the page and configure a AsyncPostBackTrigger trigger for the OnTick event of the Timer control. This latter technique enables you to update several UpdatePanel controls at once at regular intervals. An example of using a timer control would be to periodically update an UpdatePanel containing an AdRotator control.

To add a timer trigger to an UpdatePanel control:

1. Add a Timer control to your Web page.

2. Set the Interval property of the Timer control to the length of time, in milliseconds, that you want to have between partial-page postbacks.

3. If the Timer control is not contained in the of an UpdatePanel control, follow the procedure To add a AsyncPostBackTrigger trigger to an UpdatePanel control: and specify that the Tick event of the Timer control should be used to trigger updates.

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