even you can do this by Gettype
Using the Form PrentForm propertie,Controls we csan find for E.g.
if (this.ParentForm.GetType() == typeof(ParentFormName)) ///Where In typeof() containss our parent form Name
((ParentFormName)this.ParentForm).Label1.Text= "HI"; // where ResultId is my Parent form propertie.
Thanks for ur response.. But i was unable to get the form name of the master page.
Actually my requirement is
I had a iframe pop-up in my master page that was hidden by default but when there is a requirement it was made unhidden. So the page which we want to show in that iframe is appended to it my giving iframe src as the page name. Here i had a close button in my iframe(master page) anf want to access that in my child page(iframe). when using Master.FindControl property it was showing as null and when i add masterfilename property in register tag of aspx page it is showing the whole master page in the iframe pop-up.
Can anyone please send how can i access my parent control by adding masterfilename but not to show the whole page in the iframe pop-up.