WinForm下ComboBox设定SelectedValue总结

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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] view plain copy print ?

1. private void SetValueByItem()  
2.         {  
3.             Area a = new Area();  
4.             a.Area_ID = "8";  
5.             a.Area_Name = "第8名";  
6.             cbList.SelectedItem = ac.FindAll(delegate(Area ar) { return ar.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] view plain copy print ?

1. private void SetValueByValue()  
2.        {  
3.            Area a = new Area();  
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] view plain copy print ?

1. private void SetValueByText()  
2.         {  
3.             Area a = new Area();  
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] view plain copy print ?

1. using System;  
2. using System.Collections.Generic;  
3. using System.ComponentModel;  
4. using System.Data;  
5. using System.Drawing;  
6. using System.Text;  
7. using System.Windows.Forms;  
8. namespace WinFormCombobox  
9. {  
10.     public partial class frmMain : Form  
11.     {  
12.         public frmMain()  
13.         {  
14.             InitializeComponent();  
15.         }  
16.         #region Members  
17.         AreaLists ac;  
18.         public AreaLists GetTestArea()  
19.         {  
20.             AreaLists al = new AreaLists();  
21.             for (int i = 1; i < 11; i++)  
22.             {  
23.                 Area a = new Area();  
24.                 a.Area_ID = i.ToString();  
25.                 a.Area_Name = "第" + i.ToString() + "名";  
26.                 al.Add(a);  
27.             }  
28.             return al;  
29.         }  
30.         #endregion  
31.         #region Events  
32.         private void frmMain_Load(object sender, EventArgs e)  
33.         {  
34.             ac = GetTestArea();  
35.             cbList.DataSource = ac;  
36.             cbList.DisplayMember = "Area_Name";  
37.             cbList.ValueMember = "Area_ID";  
38.         }  
39.         private void btnSetCombobox_Click(object sender, EventArgs e)  
40.         {  
41.             ////SetValue0();  
42.             //SetValueByValue();  
43.             ////SetValueByItem();  
44.             SetValueByText();  
45.         }  
46.         #endregion  
47.         #region Methods  
48.         private void SetValue0()  
49.         {  
50.             Area a = new Area();  
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.         private void SetValueByValue()  
60.         {  
61.             Area a = new Area();  
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.         private void SetValueByItem()  
68.         {  
69.             Area a = new Area();  
70.             a.Area_ID = "8";  
71.             a.Area_Name = "第8名";  
72.             cbList.SelectedItem = ac.FindAll(delegate(Area ar) { return ar.Area_ID == a.Area_ID; })[0];  
73.             lbResult.Text = cbList.SelectedItem.GetType().ToString() + ":" + cbList.SelectedValue.ToString();  
74.         }  
75.         private void SetValueByText()  
76.         {  
77.             Area a = new Area();  
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. }  
86.   
87. using System;  
88. using System.Collections.Generic;  
89. using System.Text;  
90. namespace WinFormCombobox  
91. {  
92.     #region Area  
93.     public class Area  
94.     {  
95.         private string m_Area_ID;  
96.         public string Area_ID  
97.         {  
98.             get { return m_Area_ID; }  
99.             set { m_Area_ID = value; }  
100.         }  
101.         private string m_Area_Name;  
102.         public string Area_Name  
103.         {  
104.             get { return m_Area_Name; }  
105.             set { m_Area_Name = value; }  
106.         }  
107.         private double m_Area_Order;  
108.         public double Area_Order  
109.         {  
110.             get { return m_Area_Order; }  
111.             set { m_Area_Order = value; }  
112.         }  
113.     }  
114.     #endregion  
115.     [Serializable]  
116.     public class AreaLists : List<Area>  
117.     {  
118.         private int _maxItems = 0;  
119.         public int MaxItems { get { return this._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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