问如何从Dropdownlist中选择一个值并将值传递给Gridview？

EN

public void RefreshDay()
        {
            SqlConnection conn = new SqlConnection(@"data source =.\sqlexpress; integrated security = true; database = DBdentist");
            SqlDataAdapter da = null;
            DataSet ds = null;
            DataTable dt = null;
            string sqlsel = "SELECT Distinct patient.patientID, day from patient, patientreservation where patient.patientID = patientreservation.patientID";


        try
        {

            da = new SqlDataAdapter();  
            da.SelectCommand = new SqlCommand(sqlsel, conn);  
            ds = new DataSet();
            da.Fill(ds, "myDay");   
            dt = ds.Tables["myDay"];   


            DropDownListDay.DataSource = dt;
            DropDownListDay.DataTextField = "day";
            DropDownListDay.DataValueField = "patientID";
            DropDownListDay.DataBind();
            DropDownListDay.Items.Insert(0, "Select Day"); 
        }
        catch (Exception ex)
        {
            LabelDay.Text = ex.Message; 
        }
        finally
        {
            conn.Close(); 
        }

    }



    protected void DropDownListDay_SelectedIndexChanged(object sender, EventArgs e)
    {
        if (DropDownListDay.SelectedIndex != 0)
        {
            SqlConnection conn = new SqlConnection(@"data source =.\sqlexpress; integrated security = true; database = DbDentist");
            SqlDataAdapter da = null;
            DataSet ds = null;
            DataTable dt = null;
            string sqlsel = "SELECT patientreservation.patientID, patient.firstname, patient.lastname, patientreservation.day, patientreservation.hour, treatment.treatment FROM((patientreservation INNER JOIN patient ON patientreservation.patientID = patient.patientID) INNER JOIN treatment ON patientreservation.treatmentID = treatment.treatmentID) WHERE patientreservation.day = " + DropDownListDay.SelectedValue + "";

            try
            {

                da = new SqlDataAdapter();  
                da.SelectCommand = new SqlCommand(sqlsel, conn); 
                ds = new DataSet();
                da.Fill(ds, "myDay");  
                dt = ds.Tables["myDay"];
                GridViewDay.DataSource = dt; 
                GridViewDay.DataBind();

            }
            catch (Exception ex)
            {
                LabelDay.Text = ex.Message; 
            }
            finally
            {
                conn.Close(); 
            }

        }

        else
        {
            LabelDay.Text = "You choose None:";
        }
    }
}

}