Problem With Select Stored Procedure

i have this stored procedure:
 
ALTER PROCEDURE dbo.SearchContact
@searchCriteria nvarchar(128)
AS
    Select FstNam1,FstNam02 from Contacts where FstNam1 like '%'+@searchCriteria+'%'
    RETURN
 
In my .aspx i have a SqlDataSource named SqlDataSource1 which have asocciated this stored procedure to select operation and parameter source of 'searchCriteria' is Control and ControlID  is "TextBox1".
Also i have a gridview with source this sqlDataSource1 and a button . When i click this button i want to take value entered in textbox and send it to above stored procedure and show returned infos in my gridview.
 i put in
Button1_Click(object sender, EventArgs e)
{ 
SqlDataSource1.SelectParameters["searchCriteria"].DefaultValue = Session["searchContact"].ToString();
xxxxxx
 }
 
 
what i need to have to xxxxx to work fine ?
 I searched for a solution and i find a lot of posibilities, but all are fragmented.........pls give a solution ...

thx for help.
 
 
P.S: Sorry for my english.