App Click Back button does not exit, double click Back key to Exit

Direct code

    //Returns the previous page without exiting when the return key is pressed, GoBack () indicates that the previous page of the WebView is returned     Public BooleanOnKeyDown (intKeycoder, KeyEvent event) {        if(!Webview1.cangoback ())                  {exit (); return false; }        if(Keycoder = =keyevent.keycode_back)               {Webview1.goback ();              Exit (); return false; }        Else{             return Super. OnKeyDown (Keycoder, event); }    }     Public voidexit () {if(!isexit) {Isexit=true; Toast.maketext (Getapplicationcontext (),"Press one more time to exit the program", Toast.length_short). Show (); Meshandler.sendemptymessagedelayed (0, 2000); } Else{Intent Intent=NewIntent (Intent.action_main);              Intent.addcategory (Intent.category_home);              StartActivity (Intent); System.exit (0); }      }