实现两级下拉框的联动(2)

//实例化SubjectBLL SubjectBLL sb = new SubjectBLL(); //年级下拉框属性更改值触发的事件 private void cbograde_SelectedIndexChanged(object sender, EventArgs e) { //获取年级编号 int id= Convert.ToInt32(cbograde.SelectedValue); //调用BLL层的方法用Subject类型的集合接收 List<Subject> list= sb.SelectSubjectInfos(id); //在科目下来框中添加一项全部。 list.Insert(0, new Subject {SubjectId=-1, SubjectName="全部" }); //清空下拉框数据 cbosubject.DataSource = null; //绑定显示值 cbosubject.DisplayMember = "subjectname"; //绑定隐藏值 cbosubject.ValueMember = "subjectid"; //绑定数据源 cbosubject.DataSource = list; }