protected void showButton_Click(object sender, EventArgs e)
 {
     reportGridView.DataSource = aDiseaseManager.GetDiseaseWiseReportsBetweenDates(diseaseDropDownList.Text,
                                                                                   DateTime.Parse(firstDateTextBox.Value), DateTime.Parse(lastDateTextBox.Value));
     reportGridView.DataBind();
     ViewState["data"] = aDiseaseManager.GetDiseaseWiseReportsBetweenDates(diseaseDropDownList.Text,
                                                                           DateTime.Parse(firstDateTextBox.Value), DateTime.Parse(lastDateTextBox.Value));
 }