private DataSet ds = null;//
public FrmScoreQuary()
{
InitializeComponent();
this.cboClass.DataSource = new StudentService().GetAllStudentBySet().Tables[0];
this.cboClass.DisplayMember = "ClassName";
this.cboClass.ValueMember = "ClassId";
this.cboClass.SelectedIndex = -1;
ds = objScoreListService.GetAllScoreBySet();
this.dgvScoreList.DataSource = ds.Tables[0];
this.cboClass.SelectedIndexChanged += new System.EventHandler(this.cboClass_SelectedIndexChanged);
}