Show modal dialog from C# after saving items into list

Hi,

I need to open the SP2010 modal popup(SP.UI.ModalDialog) from C# code in button click event. During this button click, i need to save some records to SP list too.

I tried btn.attributes.add. It shows the popup before saving the record itself. I cannot use "Onclientclick" as i am doing some validations using server side validators.

What could be the effective method?