this is my code...i just try to search the result by the name of school.but the grid view didnt show any thing.my code is

```
public void gridfill()
{
    markSp spMark = new markSp();
    DataTable dtbl = new DataTable();
    dtbl = spMark.markViewAll();
    gvResult.DataSource = dtbl;
    dtbl = spMark.markViewBySchool(txtSchoolName.Text);
    gvResult.DataSource = dtbl;    
}
protected void Button1_Click(object sender, EventArgs e)
{
    gridfill();
}
public DataTable markViewAll()
{
    DataTable dtbl = new DataTable();
    SqlDataAdapter sqlda = new SqlDataAdapter("markViewAll", sqlcon);
    sqlda.SelectCommand.CommandType = CommandType.StoredProcedure;
    sqlda.Fill(dtbl);
    return dtbl;
}
public DataTable markViewBySchool(string viewBySchool)
{
    DataTable dtbClass = new DataTable();
    SqlDataAdapter sqlda = new SqlDataAdapter("markViewBySchool",sqlcon);
    sqlda.SelectCommand.CommandType = CommandType.StoredProcedure;
    sqlda.SelectCommand.Parameters.Add("@schoolName", SqlDbType.VarChar).Value = viewBySchool;
    sqlda.Fill(dtbClass);
    return dtbClass;
}

```