To Add data from Grid View have input controls in Grid Footer and set ShowFooter to Ture
and have Button give Commond Name, In RowCommond event use following logic..
protected void GridView1_RowCommand(object sender, GridViewCommandEventArgs e)
{
if (e.CommandName == "AddItem")
{
Control controlRefName = GridView1.FooterRow.FindControl("controlID") as Control;
.
.
}
}