what is the main purpose of UpdatePanel in ASP.Net ? And what is the of Triggers tag in UpdatePanel ?
An UpdatePanelis a set of components that you want to be affected by ajaxified updates in your webapplication. The triggers are what causes the panel of components to update.
If you want to know more about asp.net ajax and update panel please read How Ajax for ASP.NET updatepanels work.
来源：https://stackoverflow.com/questions/2904231/what-is-the-updatepanel