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问题:
I need a Generic function to retrieve the name or value of an enum based on the XmlEnumAttribute "Name" property of the enum. For example I have the following enum defined:
Public Enum Currency CDN = 1 USA= 2 EUR= 3 JPN= 4 End Enum
The first Currency enum value is 1; the enum name is "CDN"; and the XMLEnumAttribute Name property value is "00".
If I have the enum value, I can retrieve the XmlEnumAttribute "Name" value using the following generic function:
Public Function GetXmlAttrNameFromEnumValue(Of T)(ByVal pEnumVal As T) As String Dim type As Type = pEnumVal.GetType Dim info As FieldInfo = type.GetField([Enum].GetName(GetType(T), pEnumVal)) Dim att As XmlEnumAttribute = CType(info.GetCustomAttributes(GetType(XmlEnumAttribute), False)(0), XmlEnumAttribute) 'If there is an xmlattribute defined, return the name Return att.Name End Function
So using the above function, I can specify the Currency enum type, pass a value of 1, and the return value will be "00".
What I need is a function to perform if the opposite. If I have the XmlEnumAttribute Name value "00", I need a function to return a Currency enum with a value of 1. Just as useful would be a function that would return the enum name "CDN". I could then simply parse this to get the enum value.
Any assistance would be appreciated.
回答1:
A requirement to solve this exact same problem led me to this question and answer. As I develop in VB.NET, I rewrote CkH's solution into VB and modified it to use your GetXmlAttrNameFromEnumValue function.
Public Shared Function GetCode(Of T)(ByVal value As String) As T For Each o As Object In System.Enum.GetValues(GetType(T)) Dim enumValue As T = CType(o, T) If GetXmlAttrNameFromEnumValue(Of T)(enumValue).Equals(value, StringComparison.OrdinalIgnoreCase) Then Return CType(o, T) End If Next Throw New ArgumentException("No code exists for type " + GetType(T).ToString() + " corresponding to value of " + value) End Function
C# Version:
public static string GetXmlAttrNameFromEnumValue(T pEnumVal) { // http://stackoverflow.com/q/3047125/194717 Type type = pEnumVal.GetType(); FieldInfo info = type.GetField(Enum.GetName(typeof(T), pEnumVal)); XmlEnumAttribute att = (XmlEnumAttribute)info.GetCustomAttributes(typeof(XmlEnumAttribute), false)[0]; //If there is an xmlattribute defined, return the name return att.Name; } public static T GetCode(string value) { // http://stackoverflow.com/a/3073272/194717 foreach (object o in System.Enum.GetValues(typeof(T))) { T enumValue = (T)o; if (GetXmlAttrNameFromEnumValue(enumValue).Equals(value, StringComparison.OrdinalIgnoreCase)) { return (T)o; } } throw new ArgumentException("No XmlEnumAttribute code exists for type " + typeof(T).ToString() + " corresponding to value of " + value); }
回答2:
I do something similar with custom attributes and I use this method to get the EnumValue based on the Attribute Value. GetStringValue is my custom method, similar to your example above.
public static class Enums { public static T GetCode(string value) { foreach (object o in System.Enum.GetValues(typeof(T))) { if (((Enum)o).GetStringValue().Equals(value, StringComparison.OrdinalIgnoreCase)) return (T)o; } throw new ArgumentException("No code exists for type " + typeof(T).ToString() + " corresponding to value of " + value); } }
For the whole process I use check this post and the answers: Extending Enums, Overkill?
Sorry this is in C#, just realized you were using VB.NET above.
回答3:
Slightly modified from: http://www.wackylabs.net/2006/06/getting-the-xmlenumattribute-value-for-an-enum-field/
public static string ToString2 (this Enum e) { // Get the Type of the enum Type t = e.GetType (); // Get the FieldInfo for the member field with the enums name FieldInfo info = t.GetField (e.ToString ("G")); // Check to see if the XmlEnumAttribute is defined on this field if (!info.IsDefined (typeof (XmlEnumAttribute), false)) { // If no XmlEnumAttribute then return the string version of the enum. return e.ToString ("G"); } // Get the XmlEnumAttribute object[] o = info.GetCustomAttributes (typeof (XmlEnumAttribute), false); XmlEnumAttribute att = (XmlEnumAttribute)o[0]; return att.Name; }
回答4:
@Dean, @Jason and @Camron, thank you for your solutions. Your solutions helped me in solving my problem, where, given an XmlEnumAttribute name, the actual enum value was needed.
My variant is mentioned here.
回答5:
Here's a variation that generates a dictionary from the enum, allowing you to potentially cache the reflection part of it should you need to use it a lot.
/// /// Generates a dictionary allowing you to get the csharp enum value /// from the string value in the matching XmlEnumAttribute. /// You need this to be able to dynamically set entries from a xsd:enumeration /// when you've used xsd.exe to generate a .cs from the xsd. /// https://msdn.microsoft.com/en-us/library/x6c1kb0s(v=vs.110).aspx /// /// The xml enum type you want the mapping for /// Mapping dictionary from attribute values (key) to the actual enum values /// T must be an enum private static Dictionary GetEnumMap() where T : struct, IConvertible { if (!typeof(T).IsEnum) { throw new ArgumentException("T must be an enum"); } var members = typeof(T).GetMembers(); var map = new Dictionary(); foreach (var member in members) { var enumAttrib = member.GetCustomAttributes(typeof(XmlEnumAttribute), false).FirstOrDefault() as XmlEnumAttribute; if (enumAttrib == null) { continue; } var xmlEnumValue = enumAttrib.Name; var enumVal = ((FieldInfo)member).GetRawConstantValue(); map.Add(xmlEnumValue, (T)enumVal); } return map; }
usage:
var map = GetEnumMap(); return map["02"]; // returns Currency.EUR
