ComboBox的數據聯動 - WJ-163－IT工程師數位筆記本

文章出處

實現效果：

點擊年級下拉框值時，獲取科目下拉框值

一：加載年級下拉框值

GradeDAL層：

      //檢索所有年級名稱集合，返回的是泛型集合List<Grade>
      public List<Grade> GetAllGrade()
      {
          string sql = "select * from  Grade";
          //將sql轉成內存中的一張表
          DataTable dt = SQLHelper.ExecuteDataTable(sql);
          MyTool tool = new MyTool();
          //dt轉成list
          List<Grade> list = tool.DataTableToList<Grade>(dt);
          return list;
      
      
      }

GradeBLL層：

        //植入DAL層的對象
        GradeDAL gradeDal=new GradeDAL();
        public List<Grade> GetAllGrade()
        {
            return gradeDal.GetAllGrade();
        }

UI層：

  private void frmSelectResult_Load(object sender, EventArgs e)
        {
            //清空
            cboSubject.DropDownHeight = 106;

            GradeBLL gradeBll = new GradeBLL();
            //對年級下拉框綁定數據
            List<Grade> list = gradeBll.GetAllGrade();
           
            cboGrade.ValueMember = "GradeId";
            cboGrade.DisplayMember = "GradeName";
            cboGrade.DataSource = list;

           // flag = true;
        }

二：根據年級編號，去加載科目下拉框數據

1.在DAL層寫一個根據年級編號獲取科目集合的方法

SubjectDAL層：

   public List<Subject> GetAllSubject(int id)
       {
           string sql = "select * from Subject where GradeId=@Id";
           SqlParameter para = new SqlParameter("@Id",id);
           DataTable dt = SQLHelper.ExecuteDataTable(sql,para);
           MyTool tool = new MyTool();
           List<Subject> list= tool.DataTableToList<Subject>(dt);
           return list;
       
       }

2.Bll層做數據傳遞

      SubjectDAL subjectDal = new SubjectDAL();

      public List<Subject> GetAllSubject(int id)
      {
          return subjectDal.GetAllSubject(id);
      }

3.UI層下拉框選中項發生改變的事件：SelectedIndexChanged

        SubjectBLL subBll = new SubjectBLL();
        private void cboGrade_SelectedIndexChanged(object sender, EventArgs e)
        {
           // if (flag)
           // {
                int selectid = Convert.ToInt32(cboGrade.SelectedValue);
                List<Subject> list = subBll.GetAllSubject(selectid);

                cboSubject.ValueMember = "SubjectId";
                cboSubject.DisplayMember = "SubjectName";
                cboSubject.DataSource = list;
            //}
        }