How do retrieve the DataKey value from the Gridview ?
Please ensure your Gridview had DataKeyName properites setting.
OnRowCommand[ I set DeleMe method] event of the Gridview assign your method name.
This method takes Object and GridViewRowCommand as parameter to perform the task.
Example,If you want to delete a selected row from the Gridview,add the Linkbutton and text the "Remove" and its CommandName must be non than "Delete" and its CommandArgument,you can assign the primary key column value as <%#Eval("ecode")%>.
This LinkButton should be resides under Gridview's TemplateField and ItemTemplate.
My code goes like this..
protected void DeleMe(object sender, GridViewCommandEventArgs g)
{
if (g.CommandName == "Remove")
{
string ecode = g.CommandArgument.ToString();
Response.Write(ecode);
}
}