Click the prevent button multiple times to prevent malicious refresh

<Asp: button runat ="Server"Id ="BTN"TEXT ="Button"Onclick ="Aa_click"/>
 

Public VoidPage_load (Object OBJ, eventargs E)
 

 
{
 

BTN. Attributes. Add ("Onclick","State = true ;");
 

 
Stringbuilder sb =NewStringbuilder ();
 

SB. append ("If (! State) return ;");
 

 
SB. append ("Var button = Document. getelementbyid ('btn ');");
 

SB. append ("Button. value = 'Please wait ...';");
 

 
SB. append ("Document. Body. style. cursor = 'wait ';");
 

SB. append ("Button. Disabled = true ;");
 

 
StringStrscript ="<SCRIPT>";
 

Strscript = strscript +"Var state = false ;";
 

 
// Bind the function to the onbeforeunload event on the page:
 

 strscript = strscript + " window. attachevent ('onbeforeunload', function () {" + sb. tostring () +  "});" ; 

Strscript = strscript +"</"+"Script>";
 

 
Page. registerstartupscript ("Onbeforeunload", Strscript );
 

}
 

 
Protected VoidAa_click (ObjectSender, eventargs E)
 

{
 

 
// Simulate button processing for a long time
 

 system. threading. thread. sleep (2000); 

Response. Write ("<SCRIPT> alert ('bbbbbb !! ');"+"</"+"Script>");
 

 
}