public void GetAllTeacherByDepartment() { Teachers _Teachers = new Teachers(); _Teachers.DepartmentId = Convert.ToInt32(DepartmentDropDownList.SelectedValue); TeacherDropDownList.DataSource = _CourseAssigneManager.GetAllTeacherByDepartment(_Teachers.DepartmentId); TeacherDropDownList.DataTextField = "TeacherName"; TeacherDropDownList.DataValueField = "Id"; TeacherDropDownList.DataBind(); TeacherDropDownList.Items.Insert(0, new ListItem("Select Teachers", "0")); }