how to hide null cell before rotating GridView

I want my GridView to hide the column which has null row value then rotate. I have some code below. But it is checking value after rotating. There is only one selected row and many columns.

protected void btnSearch_Click(object sender, EventArgs e)
{
gvDb.DataSource = (c());
gvDb.DataBind();
hideNull();
}
public DataSet c()
{
SqlConnection cn = new SqlConnection(cs);
cn.Open();
SqlDataAdapter ad = new SqlDataAdapter("select * from DESIGNSTABLE WHERE B210_APPL_NUMBER=" + txtID.Text + "", cn);
DataSet ds = new DataSet();
ad.Fill(ds, "DB");
gvDb.DataSource = ds;
gvDb.DataBind();
cn.Close();
return ds;
}
public DataSet FlipDataSet(DataSet my_DataSet)
{
DataSet ds = new DataSet();
foreach (DataTable dt in my_DataSet.Tables)
{
DataTable table = new DataTable();
for (int i = 0; i <= dt.Rows.Count; i++)
{
table.Columns.Add(Convert.ToString(i));
}
DataRow r = null;
for (int k = 0; k < dt.Columns.Count; k++)
{
r = table.NewRow();
r[0] = dt.Columns[k].ToString();
for (int j = 1; j <= dt.Rows.Count; j++)
r[j] = dt.Rows[j - 1][k];
table.Rows.Add(r);
}
ds.Tables.Add(table);
}
return ds;
}
protected void hideNull()
{
Boolean hasData = false;
for (int col = 0; col < gvDb.HeaderRow.Cells.Count; col++)
{
for (int row = 0; row < gvDb.Rows.Count; row++)
{
if (!String.IsNullOrEmpty(gvDb.Rows[row].Cells[col].Text)
&& !String.IsNullOrEmpty(HttpUtility.HtmlDecode(gvDb.Rows[row].Cells[col].Text).Trim()))
{
hasData = true;
break;
}
}
if (!hasData)
{
gvDb.HeaderRow.Cells[col].Visible = false;
for (int hiddenrows = 0; hiddenrows < gvDb.Rows.Count; hiddenrows++)
{
gvDb.Rows[hiddenrows].Cells[col].Visible = false;
}
}
hasData = false;
}
}