How can use window. showmodaldialog to open a. ASPX page pop up window.

Issue description

I want to use window. showmodaldialog to open a pop up window and then select a value in the pop up window and return it back to opener window. My PopUp window is. ASPX page that contains a radio button list (a list of citys ). when I select one city, it shoshould bring it back to the opener window. actually, what is happening now is that, when I click on particle city, a new blank window appears which is undesirable.
Note: The radiobuttonlist has autopostback property set to true.

Solution

Maybe you have known that IFRAME or frame is the solution, there is a sample: http://www.zzgyxx.com/bbs/dispbbs.asp? Boardid = 21 & id = 916.but I don't want to use it because it's very awkward.
There is other way can do it, just add the Code <base target = "_ Self"> on the modal web page between