I’ve first posted this tip on the 14 of May 2005 and I still get good traffic to the post. So I decided to update the post and code samples to use Framework 2.0 (I’m still not using 3.5) and improve the code somewhat.
The problem:
How do I databind my combo box to my domain object that has a property of some enum type?
The solution:
Quite simple, firstly we will create an object (EnumComboBoxItem) that would encapsulate and represent each item in the combo list data source. EnumComboBoxItem is a pure fabrication class that has two properties we’ll use when databinding to the combo. We have a Value property which is used by the ValueMember property on the combo box and EscapedValue that is used by the DisplayMember property of the combo box. Note that when we construct a new EnumComboBoxItem instance that we call the AsciiEscape method in the constructor when populating the escapedValue field.
Here is the code:
1 using System;
2 using System.Collections.Generic;
3 using System.Text.RegularExpressions;
4
5 namespace BindComboToEnum
6 {
7 ///
8 /// The enum combo box item
9 ///
10 public class EnumComboBoxItem
11 {
12 #region Constants
13
14 public const string DisplayMember = “EscapedValue”;
15 public const string ValueMember = “Value”;
16
17 #endregion
18
19 #region Readonly & Static Fields
20
21 private readonly string escapedValue;
22 private readonly object value;
23
24 #endregion
25
26 #region C’tors
27
28 ///
29 /// Initializes a new instance of the class.
30 ///
31 ///
The original value.
32 public EnumComboBoxItem(object originalValue)
33 {
34 value = originalValue;
35 escapedValue = EscapeAsciiValues(originalValue.ToString());
36 }
37
38 #endregion
39
40 #region Instance Properties
41
42 ///
43 /// Gets the escaped value.
44 ///
45 /// The escaped value.
46 public string EscapedValue
47 {
48 get { return escapedValue; }
49 }
50
51 ///
52 /// Gets the value.
53 ///
54 /// The value.
55 public object Value
56 {
57 get { return value; }
58 }
59
60 #endregion
61
62 #region Instance Methods
63
64 ///
65 /// Returns a that represents the current .
66 ///
67 ///
68 /// A that represents the current .
69 ///
70 public override string ToString()
71 {
72 return escapedValue;
73 }
74
75 #endregion
76
77 #region Class Methods
78
79 ///
80 /// Creates the data source for the enum type.
81 ///
82 ///
Type of the enum.
83 /// When the type passed is not an enum the exception is raised.
84 ///
85 /// Returns a generic list to be used as the combo datasource.
86 ///
87 public static List<object> CreateDataSourceFor(Type enumType)
88 {
89 if (!enumType.IsEnum)
90 throw new ApplicationException(“When using the Enum combo data source you are only allowed to use enum types.”);
91
92 Array enumValues = Enum.GetValues(enumType);
93
94 List<object> result = new List<object>();
95
96 for (int index = 0; index < enumValues.Length; index++)
97 {
98 result.Add(new EnumComboBoxItem(enumValues.GetValue(index)));
99 }
100
101 return result;
102 }
103
104 private static string ConvertAsciiValueToStringRepresentation(string currentRegexMatchValue)
105 {
106 string result = string.Empty;
107 const int BaseValue = 16;
108
109 if (currentRegexMatchValue.StartsWith(“0x”))
110 {
111 // grab the remainder string after the 0x
112 string asciiCodeValue = currentRegexMatchValue.Substring(2);
113 // convert the remainder string to a byte
114 byte byteValue = Convert.ToByte(asciiCodeValue, BaseValue);
115 // now we can convert to a character and find the string of the character
116 result = Convert.ToChar(byteValue).ToString();
117 }
118 return result;
119 }
120
121 private static string EscapeAsciiValues(string rawValue)
122 {
123 string result = string.Empty;
124
125 if (rawValue == null)
126 return result;
127
128 // Find 0x with any four alpha-numeric characters
129 Regex regex = new Regex(“0x[0-9A-Z]{4}”);
130
131 MatchCollection matchCollection = regex.Matches(rawValue);
132 Match matchPrevious = null;
133
134 for (int i = 0; i < matchCollection.Count; i++)
135 {
136 // if no match (ie. null) set to 0, else the current index + length
137 int startIndex = (matchPrevious == null ? 0 : matchPrevious.Index + matchPrevious.Length);
138
139 // add the part of the string that is not the ascii expression
140 result += rawValue.Substring(startIndex, matchCollection[i].Index – startIndex);
141
142 // convert the ascii expression to a normal string
143 result += ConvertAsciiValueToStringRepresentation(matchCollection[i].Value);
144
145 matchPrevious = matchCollection[i];
146 }
147
148 if (matchPrevious == null)
149 result += rawValue;
150 else
151 result += rawValue.Substring(matchPrevious.Index + matchPrevious.Length);
152
153 return result;
154 }
155
156 #endregion
157 }
158 }
The EscapeAsciiValues method is used to Replace the Ascii characters in our Enum with the character representation. We do the Ascii characters because we want our combo to display “Bi- Annual” instead of “BiAnnual”. Look at the following enum as an example:
1 namespace BindComboToEnum
2 {
3 public enum PaymentFrequencies
4 {
5 Annual = 1,
6 Bi0×00A00×002D0×00A0Annual = 2, // Bi – Annual
7 Quarterly = 4,
8 Monthly = 12,
9 Fortnightly = 26,
10 Weekly = 52
11 }
12 }
Now, all that we need is the following code behind the form to bind our Combo box and we are away:
22 private void InitDataBindings()
23 {
24 PaymentFrequencyComboBox.DataSource = EnumComboBoxItem.CreateDataSourceFor(typeof(PaymentFrequencies));
25 PaymentFrequencyComboBox.DisplayMember = EnumComboBoxItem.DisplayMember;
26 PaymentFrequencyComboBox.ValueMember = EnumComboBoxItem.ValueMember;
27 PaymentFrequencyComboBox.DataBindings.Add(“SelectedValue”, new Loan(), “PaymentFrequency”);
28 }
The EnumComboBoxItem.CreateDataSourceFor method creates an List<object> for us to use as a data source for the combo box.
And there you have it, a Combobox bound to an Enum!
