protected void Page_Load(object sender, EventArgs e)
        {
            if (!IsPostBack)
            {
                ClassBLL   classBLL = new ClassBLL();
                CourseBLL  courBLL  = new CourseBLL();
                TeacherBLL teachBLL = new TeacherBLL();
                //绑定页面查询条件的数据
                DropDownList_class.DataSource    = classBLL.getAll();
                DropDownList_class.DataTextField = "name";
                DropDownList_class.DataBind();
                DropDownList_class.Items.Insert(0, "全部班级");

                DropDownList_course.DataSource    = courBLL.getAll();
                DropDownList_course.DataTextField = "name";
                DropDownList_course.DataBind();
                DropDownList_course.Items.Insert(0, "全部课程");

                DropDownList_teacher.DataSource    = teachBLL.getTeachers();
                DropDownList_teacher.DataTextField = "name";
                DropDownList_teacher.DataBind();
                DropDownList_teacher.Items.Insert(0, "全部教师");

                bind();
            }
        }
        /// <summary>
        /// 绑定数据源
        /// </summary>
        private void bind()
        {
            CourseBLL  courBLL    = new CourseBLL();
            TeacherBLL teacherBLL = new TeacherBLL();
            ClassBLL   classBLL   = new ClassBLL();

            //绑定 "课程名称" 数据源
            DropDownList_course.DataSource     = courBLL.getAll();
            DropDownList_course.DataTextField  = "name";
            DropDownList_course.DataValueField = "ID";
            DropDownList_course.DataBind();

            //绑定 "任课老师" 数据源
            DropDownList_teacher.DataSource     = teacherBLL.getTeachers();
            DropDownList_teacher.DataTextField  = "name";
            DropDownList_teacher.DataValueField = "ID";
            DropDownList_teacher.DataBind();

            //绑定 "班级名称" 数据源
            DropDownList_class.DataSource     = classBLL.getAll();
            DropDownList_class.DataTextField  = "name";
            DropDownList_class.DataValueField = "ID";
            DropDownList_class.DataBind();
        }