Modal PopUp and Boostrap

I need create a user control with a generic modal popup with the buttons yes/no, I copied the code from bootstrap site and when call to my control ascx with the modal with the next instruction, show the modal without problems

ScriptManager.RegisterClientScriptBlock(this, this.GetType(), "none", "", false);

but my problem is when I try of return the data yes or not, I dont know how to do this, I tried with hidden fields, with properties in the control, but nothing ....

when i call to the control with the line ScriptManager, this continue and dont stop like the messagebox in desktop and return a value with the next instruction string x= messagebox("do you want delete the field")

please help me.