使用枚举类保持枚举对象映射？ [英] Keep enum-to-object mapping with enum class?
问题描述
正如你所看到的，在这个例子中，创建了一个有一个静态字段的烦人的类。 / p>
public enum EmailTemplates
{
//记住编辑相应的映射单例！
WelcomeEmail，
ConfirmEmail
}
public class KnownTemplates
{
public static Dictionary< EmailTemplates，string> KnownTemplates;
static KnownTemplates（）{
KnownTemplates.Add（EmailTemplates.WelcomeEmail，File1.htm）;
KnownTemplates.Add（EmailTemplates.ConfirmEmail，File2.htm）;
}
}
有时，映射类可以有更多的功能和有意义的名称，映射活动甚至可以是私有的。但是这只会污染维护/相关问题。
任何人都有一个很好的模式？
您可以使用属性来注释枚举，然后使用反射来构建字典。
AttributeUsage（AttributeTargets.Field）]
密封类TemplateAttribute：属性{
public TemplateAttribute（String fileName）{
FileName = fileName;
}
public String FileName {get;组;
}
枚举EmailTemplate {
[Template（File1.htm）]
WelcomeEmail，
[Template（File2.htm）]
ConfirmEmail
}
class KnownTemplates {
static Dictionary< EmailTemplate ，String> knownTemplates;
static KnownTemplates（）{
knownTemplates = typeof（EmailTemplates）
.GetFields（BindingFlags.Static | BindingFlags.Public）
.Where（fieldInfo =>属性.IsDefined（fieldInfo，typeof（TemplateAttribute）））
.Select（
fieldInfo => new {
Value =（EmailTemplate）fieldInfo.GetValue（null），
Template = （TemplateAttribute）属性
.GetCustomAttribute（fieldInfo，typeof（TemplateAttribute））
}
）
.ToDictionary（x => x.Value，x => x.Template 。文件名）;
}
}
如果你这么做可以创建一个更通用的通用函数，将枚举值与与该枚举值相关联的属性组合起来：
static IEnumerable< Tuple< TEnum ，TAttribute>>> GetEnumAttributes< TEnum，TAttribute>（）
其中TEnum：struct
其中TAttribute：Attribute {
return typeof（TEnum）
.GetFields（BindingFlags.Static | BindingFlags.Public）
.Where（fieldInfo => Attribute.IsDefined（fieldInfo，typeof（TAttribute）））
.Select（
fieldInfo => Tuple.Create（
（TEnum）fieldInfo。 GetValue（null），
（TAttribute）Attribute.GetCustomAttribute（fieldInfo，typeof（TAttribute））
）
）;
}
使用如下：
knownTemplates = GetEnumAttributes< EmailTemplate，TemplateAttribute>（）
.ToDictionary（tuple => tuple.Item1，tuple => tuple.Item2.FileName）;
为了更好玩，您可以创建一个扩展方法：
static class EmailTemplateExtensions {
static Dictionary< EmailTemplate，String>模板;
static EmailTemplateExtensions（）{
templates = GetEnumAttributes< EmailTemplate，TemplateAttribute>（）
.ToDictionary（tuple => tuple.Item1，tuple => tuple.Item2。文件名）;
}
public static String FileName（this EmailTemplate emailTemplate）{
String fileName;
if（templates.TryGetValue（emailTemplate，out fileName））
return fileName;
throw new ArgumentException（
String.Format（No template defined for EmailTemplate。{0}，emailTemplate）
）;
}
}
然后调用 EmailTemplate.ConfirmEmail.FileName（）将返回 File2.htm 。
I frequently need a global hard-coded mapping between an enum and another object (a string in this example). I want to co-locate the enum and mapping definitions to clarify maintenance.
As you can see, in this example, an annoying class with one static field is created.
public enum EmailTemplates
{
// Remember to edit the corresponding mapping singleton!
WelcomeEmail,
ConfirmEmail
}
public class KnownTemplates
{
public static Dictionary<EmailTemplates, string> KnownTemplates;
static KnownTemplates() {
KnownTemplates.Add(EmailTemplates.WelcomeEmail, "File1.htm");
KnownTemplates.Add(EmailTemplates.ConfirmEmail, "File2.htm");
}
}
Sometimes the mapping class can have more function and a meaningful name, and the mapping activity can even be private. But that only pollutes the maintenance/correlation problem.
Anyone have a good pattern for this?
You can use attributes to annotate the enumeration and then use reflection to build the dictionary.
[AttributeUsage(AttributeTargets.Field)]
sealed class TemplateAttribute : Attribute {
public TemplateAttribute(String fileName) {
FileName = fileName;
}
public String FileName { get; set; }
}
enum EmailTemplate {
[Template("File1.htm")]
WelcomeEmail,
[Template("File2.htm")]
ConfirmEmail
}
class KnownTemplates {
static Dictionary<EmailTemplate, String> knownTemplates;
static KnownTemplates() {
knownTemplates = typeof(EmailTemplates)
.GetFields(BindingFlags.Static | BindingFlags.Public)
.Where(fieldInfo => Attribute.IsDefined(fieldInfo, typeof(TemplateAttribute)))
.Select(
fieldInfo => new {
Value = (EmailTemplate) fieldInfo.GetValue(null),
Template = (TemplateAttribute) Attribute
.GetCustomAttribute(fieldInfo, typeof(TemplateAttribute))
}
)
.ToDictionary(x => x.Value, x => x.Template.FileName);
}
}
If you do this a lot you can create a more general generic function that combines enumeration values with an attribute associated with that enumeration value:
static IEnumerable<Tuple<TEnum, TAttribute>> GetEnumAttributes<TEnum, TAttribute>()
where TEnum : struct
where TAttribute : Attribute {
return typeof(TEnum)
.GetFields(BindingFlags.Static | BindingFlags.Public)
.Where(fieldInfo => Attribute.IsDefined(fieldInfo, typeof(TAttribute)))
.Select(
fieldInfo => Tuple.Create(
(TEnum) fieldInfo.GetValue(null),
(TAttribute) Attribute.GetCustomAttribute(fieldInfo, typeof(TAttribute))
)
);
}
And use it like this:
knownTemplates = GetEnumAttributes<EmailTemplate, TemplateAttribute>()
.ToDictionary(tuple => tuple.Item1, tuple => tuple.Item2.FileName);
For even more fun you can create an extension method:
static class EmailTemplateExtensions {
static Dictionary<EmailTemplate, String> templates;
static EmailTemplateExtensions() {
templates = GetEnumAttributes<EmailTemplate, TemplateAttribute>()
.ToDictionary(tuple => tuple.Item1, tuple => tuple.Item2.FileName);
}
public static String FileName(this EmailTemplate emailTemplate) {
String fileName;
if (templates.TryGetValue(emailTemplate, out fileName))
return fileName;
throw new ArgumentException(
String.Format("No template defined for EmailTemplate.{0}.", emailTemplate)
);
}
}
Then calling EmailTemplate.ConfirmEmail.FileName() will return File2.htm.
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