WinForm下ComboBox设定SelectedValue总结

最近在项目中处理一个winForm中设定ComboBox值，奇怪的是用一个对象匹配ComboBox的Datasource集合的一个对象时，设置SelectedValue时，竟然得到SelectedValue为null。

网上搜索一下，有说是如果用DateSet绑定时，SelectedValue得到的是null或DataRowView。

后来反复实践，发现可以用以下方法实现：

  

   
   private
    
   void
    SetValueByItem()
 {
 Area a 
   =
    
   new
    Area();
 a.Area_ID 
   =
    
   "
   8
   "
   ;
 a.Area_Name 
   =
    
   "
   第8名
   "
   ;

  cbList.SelectedItem 
   = ac.FindAll(delegate(Area ar) { return ar.Area_ID == a.Area_ID; })[0
   ];
 lbResult.Text 
   =
    cbList.SelectedItem.GetType().ToString() 
   +
    
   "
   :
   "
    
   +
    cbList.SelectedValue.ToString();
 }
  

其他两种设置方式：

  

   
    
   private
    
   void
    SetValueByValue()
 {
 Area a 
   =
    
   new
    Area();
 a.Area_ID 
   =
    
   "
   8
   "
   ;
 a.Area_Name 
   =
    
   "
   第8名
   "
   ;

 cbList.SelectedValue 
   =
    a.Area_ID;
 lbResult.Text 
   =
    cbList.SelectedValue.GetType().ToString() 
   +
    
   "
   :
   "
    
   +
    cbList.SelectedValue.ToString();
 }
  

  

   
    
   private
    
   void
    SetValueByText()
 {
 Area a 
   =
    
   new
    Area();
 a.Area_ID 
   =
    
   "
   8
   "
   ;
 a.Area_Name 
   =
    
   "
   第8名
   "
   ;

 cbList.SelectedIndex 
   =
    cbList.FindString(a.Area_Name);
 lbResult.Text 
   =
    cbList.SelectedValue.GetType().ToString() 
   +
    
   "
   :
   "
    
   +
    cbList.SelectedValue.ToString();
 }
  

完整代码：

  

   
   using
    System;

   using
    System.Collections.Generic;

   using
    System.ComponentModel;

   using
    System.Data;

   using
    System.Drawing;

   using
    System.Text;

   using
    System.Windows.Forms;


   namespace
    WinFormCombobox
{
 
   public
    
   partial
    
   class
    frmMain : Form
 {
 
   public
    frmMain()
 {
 InitializeComponent();
 }
 
   #region
    Members
   
 AreaLists ac;
 
   public
    AreaLists GetTestArea()
 {
 AreaLists al 
   =
    
   new
    AreaLists();
 
   for
    (
   int
    i 
   =
    
   1
   ; i 
   <
    
   11
   ; i
   ++
   )
 {
 Area a 
   =
    
   new
    Area();
 a.Area_ID 
   =
    i.ToString();
 a.Area_Name 
   =
    
   "
   第
   "
    
   +
    i.ToString() 
   +
    
   "
   名
   "
   ;
 al.Add(a);
 }
 
   return
    al;
 }

 
   #endregion
   

 
   #region
    Events
   
 
   private
    
   void
    frmMain_Load(
   object
    sender, EventArgs e)
 {
 ac 
   =
    GetTestArea();
 cbList.DataSource 
   =
    ac;
 cbList.DisplayMember 
   =
    
   "
   Area_Name
   "
   ;
 cbList.ValueMember 
   =
    
   "
   Area_ID
   "
   ;
 }
 
   private
    
   void
    btnSetCombobox_Click(
   object
    sender, EventArgs e)
 {
 
   ///
   /SetValue0();
   

    
   //
   SetValueByValue();
   

    
   ///
   /SetValueByItem();
   

    SetValueByText();

 }
 
   #endregion
   

 
   #region
    Methods
   

 
   private
    
   void
    SetValue0()
 {
 Area a 
   =
    
   new
    Area();
 a.Area_ID 
   =
    
   "
   8
   "
   ;
 a.Area_Name 
   =
    
   "
   第8名
   "
   ;

 cbList.DataSource 
   =
    GetTestArea();
 cbList.DisplayMember 
   =
    
   "
   Area_Name
   "
   ;
 cbList.ValueMember 
   =
    
   "
   Area_ID
   "
   ;
 cbList.SelectedValue 
   =
    a.Area_ID;
 lbResult.Text 
   =
    cbList.SelectedValue.ToString();
 }

 
   private
    
   void
    SetValueByValue()
 {
 Area a 
   =
    
   new
    Area();
 a.Area_ID 
   =
    
   "
   8
   "
   ;
 a.Area_Name 
   =
    
   "
   第8名
   "
   ;

 cbList.SelectedValue 
   =
    a.Area_ID;
 lbResult.Text 
   =
    cbList.SelectedValue.GetType().ToString() 
   +
    
   "
   :
   "
    
   +
    cbList.SelectedValue.ToString();
 }

 
   private
    
   void
    SetValueByItem()
 {
 Area a 
   =
    
   new
    Area();
 a.Area_ID 
   =
    
   "
   8
   "
   ;
 a.Area_Name 
   =
    
   "
   第8名
   "
   ;

 cbList.SelectedItem 
   =
    ac.FindAll(
   delegate
   (Area ar) { 
   return
    ar.Area_ID 
   ==
    a.Area_ID; })[
   0
   ];
 lbResult.Text 
   =
    cbList.SelectedItem.GetType().ToString() 
   +
    
   "
   :
   "
    
   +
    cbList.SelectedValue.ToString();
 }

 
   private
    
   void
    SetValueByText()
 {
 Area a 
   =
    
   new
    Area();
 a.Area_ID 
   =
    
   "
   8
   "
   ;
 a.Area_Name 
   =
    
   "
   第8名
   "
   ;

 cbList.SelectedIndex 
   =
    cbList.FindString(a.Area_Name);
 lbResult.Text 
   =
    cbList.SelectedValue.GetType().ToString() 
   +
    
   "
   :
   "
    
   +
    cbList.SelectedValue.ToString();
 }
 
   #endregion
   
 }
}



   using
    System;

   using
    System.Collections.Generic;

   using
    System.Text;


   namespace
    WinFormCombobox
{
 
   #region
    Area
   
 
   public
    
   class
    Area
 {
 
   private
    
   string
    m_Area_ID;
 
   public
    
   string
    Area_ID
 {
 
   get
    { 
   return
    m_Area_ID; }
 
   set
    { m_Area_ID 
   =
    value; }
 }

 
   private
    
   string
    m_Area_Name;
 
   public
    
   string
    Area_Name
 {
 
   get
    { 
   return
    m_Area_Name; }
 
   set
    { m_Area_Name 
   =
    value; }
 }
 
   private
    
   double
    m_Area_Order;
 
   public
    
   double
    Area_Order
 {
 
   get
    { 
   return
    m_Area_Order; }
 
   set
    { m_Area_Order 
   =
    value; }
 }
 }
 
   #endregion
   

 [Serializable]
 
   public
    
   class
    AreaLists : List
   <
   Area
   >
   
 {
 
   private
    
   int
    _maxItems 
   =
    
   0
   ;
 
   public
    
   int
    MaxItems { 
   get
    { 
   return
    
   this
   ._maxItems; } 
   set
    { 
   this
   ._maxItems 
   =
    value; } }
 }
}