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C# ComboBox的联动操作（三层架构）

2019-12-30 12:26:21于海丽

02.在业务逻辑层

C#,ComboBox

 


using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using MySchool.DAL;
using System.Data;
using MySchool.Model;
namespace MySchool.BLL
{
 public class GradeBLL
 {
  GradeDAL gradedal = new GradeDAL();
  #region 获取年级数据，为在下拉框中显示

  public DataTable SelectGrade(string gradetype)
  {
   return gradedal.SelectGrade(gradetype);
  }

  public DataTable LoadCombox()
  {
   return gradedal.LoadCombox();
  }
  

  public List<Grade> Loadcombox2()
  {
   return gradedal.Loadcombox2();
  }


  #endregion

  public List<Grade> LoadCombox3()
  {
   return gradedal.LoadCombox3();
  }

  
 }
}

03.在窗体UI层

在Load事件中加载年级下拉框

 


 private void FrmSelectResult_Load(object sender, EventArgs e)
  {
   #region 加载年级下拉框
   try
   {
    List<Grade> list = gradedal.LoadCombox3();
    list.Insert(0, new Grade() { GradeId=-1,GradeName="--全部--" });
    cboGrade.ValueMember = "GradeId";
    cboGrade.DisplayMember = "GradeName";
    cboGrade.DataSource = list;
   }
   catch (Exception ex)
   {

    MessageBox.Show(ex.Message);
   }
   
   
   #endregion

   #region 加载科目下拉框
   //try
   //{
   // list2 = subjectdal.LoadComboxSub();
   // list2.Insert(0, new Subject() { SubjectId = -1, SubjectName = "--全部--" });
   // cboSubject.ValueMember = "SubjectId";
   // cboSubject.DisplayMember = "SubjectName";
   // cboSubject.DataSource = list2;
   //}
   //catch (Exception ex)
   //{

   // MessageBox.Show(ex.Message);
   //}
   
   #endregion
  }

其中在使用

获得年级下拉框隐藏值得方法（2）
int num = Convert.ToInt32(cboGrade.SelectedValue);

加载年级下拉框时：会出现的错误的写法

把cboGrade.DataSource = list;写在
 cboGrade.ValueMember = "GradeId";
 cboGrade.DisplayMember = "GradeName";上面
即：


 #region 加载年级下拉框
   try
   {
    List<Grade> list = gradedal.LoadCombox3();
    list.Insert(0, new Grade() { GradeId=-1,GradeName="--全部--" });
    cboGrade.DataSource = list;
    cboGrade.ValueMember = "GradeId";
    cboGrade.DisplayMember = "GradeName";
    
    
   }
   catch (Exception ex)
   {

    MessageBox.Show(ex.Message);
   }
   
   
   #endregion
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