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; } }    }}

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