ttoncontrol'sClickeventoraTextBoxcontrol'sTextChangedevent.Inapostbackrequest,ifthepagecontainsvalidatorcontrols,checktheIsValidpropertyofthePageandofindividualvalidationcontrolsbeforeperforminganyprocessing.Usethiseventfortasksthatrequirethatallothercontrolsonthepagebeloaded.Beforethiseventoccurs:ThePageobjectcallsEnsureChildControlsforeachcontrolandforthepage.EachdataboundcontrolwhoseDataSourceIDpropertyissetcallsitsDataBindmethod.ThePreRendereventoccursforeachcontrolonthepage.Usetheeventtomakefinalchangestothecontentsofthepageoritscontrols.Beforethiseventoccurs,ViewStatehasbeensavedforthepageandforallcontrols.Anychangestothepageorcontrolsatthispointwillbeignored.Usethiseventperformtasksthatrequireviewstatetobesaved,butthatdonotmakeanychangestocontrols.Thisisnotanevent;instead,atthisstageofprocessing,thePageobjectcallsthismethodoneachcontrol.AllASP.NETWebservercontrolshaveaRendermethodthatwritesoutthecontrol'smarkupthatissenttothebrowser.Ifyoucreateacustomcontrol,youtypicallyoverridethismethodtooutputthecontrol'smarkup.However,ifyourcustomcontrolincorporatesonlystandardASP.NETWebservercontrolsandnocustommarkup,youdonotneedtooverridetheRendermethod.Ausercontrol(an.ascxfile)automaticallyincorporatesrendering,soyoudonotneedtoexplicitlyrenderthecontrolincode.Thiseventoccursforeachcontrolandthenforthepage.Incontrols,usethiseventtodofinalcleanupforspecificcontrols,suchasclosingcontrol-specificdatabaseconnections.Forthepageitself,usethiseventtodof