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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：

[c-sharp]
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1. privatevoidSetValueByItem()
2. {
3. Areaa=newArea();
4. a.Area_ID=“8”;
5. a.Area_Name=“第8名”;
6. cbList.SelectedItem=ac.FindAll(delegate(Areaar){returnar.Area_ID==a.Area_ID;})[0];
7. lbResult.Text=cbList.SelectedItem.GetType().ToString()+“:”+cbList.SelectedValue.ToString();
8. }

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：

[c-sharp]
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1. privatevoidSetValueByValue()
2. {
3. Areaa=newArea();
4. a.Area_ID=“8”;
5. a.Area_Name=“第8名”;
6. cbList.SelectedValue=a.Area_ID;
7. lbResult.Text=cbList.SelectedValue.GetType().ToString()+“:”+cbList.SelectedValue.ToString();
8. }

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(); }

[c-sharp]
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1. privatevoidSetValueByText()
2. {
3. Areaa=newArea();
4. a.Area_ID=“8”;
5. a.Area_Name=“第8名”;
6. cbList.SelectedIndex=cbList.FindString(a.Area_Name);
7. lbResult.Text=cbList.SelectedValue.GetType().ToString()+“:”+cbList.SelectedValue.ToString();
8. }

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：

[c-sharp]
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1. usingSystem;
2. usingSystem.Collections.Generic;
3. usingSystem.ComponentModel;
4. usingSystem.Data;
5. usingSystem.Drawing;
6. usingSystem.Text;
7. usingSystem.Windows.Forms;
8. namespaceWinFormCombobox
9. {
10. publicpartialclassfrmMain:Form
11. {
12. publicfrmMain()
13. {
14. InitializeComponent();
15. }
16. #regionMembers
17. AreaListsac;
18. publicAreaListsGetTestArea()
19. {
20. AreaListsal=newAreaLists();
21. for(inti=1;i<11;i++)
22. {
23. Areaa=newArea();
24. a.Area_ID=i.ToString();
25. a.Area_Name=“第”+i.ToString()+“名”;
26. al.Add(a);
27. }
28. returnal;
29. }
30. #endregion
31. #regionEvents
32. privatevoidfrmMain_Load(objectsender,EventArgse)
33. {
34. ac=GetTestArea();
35. cbList.DataSource=ac;
36. cbList.DisplayMember=“Area_Name”;
37. cbList.ValueMember=“Area_ID”;
38. }
39. privatevoidbtnSetCombobox_Click(objectsender,EventArgse)
40. {
41. SetValue0();
42. //SetValueByValue();
43. SetValueByItem();
44. SetValueByText();
45. }
46. #endregion
47. #regionMethods
48. privatevoidSetValue0()
49. {
50. Areaa=newArea();
51. a.Area_ID=“8”;
52. a.Area_Name=“第8名”;
53. cbList.DataSource=GetTestArea();
54. cbList.DisplayMember=“Area_Name”;
55. cbList.ValueMember=“Area_ID”;
56. cbList.SelectedValue=a.Area_ID;
57. lbResult.Text=cbList.SelectedValue.ToString();
58. }
59. privatevoidSetValueByValue()
60. {
61. Areaa=newArea();
62. a.Area_ID=“8”;
63. a.Area_Name=“第8名”;
64. cbList.SelectedValue=a.Area_ID;
65. lbResult.Text=cbList.SelectedValue.GetType().ToString()+“:”+cbList.SelectedValue.ToString();
66. }
67. privatevoidSetValueByItem()
68. {
69. Areaa=newArea();
70. a.Area_ID=“8”;
71. a.Area_Name=“第8名”;
72. cbList.SelectedItem=ac.FindAll(delegate(Areaar){returnar.Area_ID==a.Area_ID;})[0];
73. lbResult.Text=cbList.SelectedItem.GetType().ToString()+“:”+cbList.SelectedValue.ToString();
74. }
75. privatevoidSetValueByText()
76. {
77. Areaa=newArea();
78. a.Area_ID=“8”;
79. a.Area_Name=“第8名”;
80. cbList.SelectedIndex=cbList.FindString(a.Area_Name);
81. lbResult.Text=cbList.SelectedValue.GetType().ToString()+“:”+cbList.SelectedValue.ToString();
82. }
83. #endregion
84. }
85. }
87. usingSystem;
88. usingSystem.Collections.Generic;
89. usingSystem.Text;
90. namespaceWinFormCombobox
91. {
92. #regionArea
93. publicclassArea
94. {
95. privatestringm_Area_ID;
96. publicstringArea_ID
97. {
98. get{returnm_Area_ID;}
99. set{m_Area_ID=value;}
100. }
101. privatestringm_Area_Name;
102. publicstringArea_Name
103. {
104. get{returnm_Area_Name;}
105. set{m_Area_Name=value;}
106. }
107. privatedoublem_Area_Order;
108. publicdoubleArea_Order
109. {
110. get{returnm_Area_Order;}
111. set{m_Area_Order=value;}
112. }
113. }
114. #endregion
115. [Serializable]
116. publicclassAreaLists:List<Area>
117. {
118. privateint_maxItems=0;
119. publicintMaxItems{get{returnthis._maxItems;}set{this._maxItems=value;}}
120. }
121. }

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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