如何通过反射获取某个类型的所有常量

虽然这是一个旧代码：

private FieldInfo[] GetConstants(System.Type type)
{
    ArrayList constants = new ArrayList();
    FieldInfo[] fieldInfos = type.GetFields(
        // Gets all public and static fields
        BindingFlags.Public | BindingFlags.Static | 
        // This tells it to get the fields from all base types as well
        BindingFlags.FlattenHierarchy);
    // Go through the list and only pick out the constants
    foreach(FieldInfo fi in fieldInfos)
        // IsLiteral determines if its value is written at 
        //   compile time and not changeable
        // IsInitOnly determines if the field can be set 
        //   in the body of the constructor
        // for C# a field which is readonly keyword would have both true 
        //   but a const field would have only IsLiteral equal to true
        if(fi.IsLiteral && !fi.IsInitOnly)
            constants.Add(fi);           
    // Return an array of FieldInfos
    return (FieldInfo[])constants.ToArray(typeof(FieldInfo));
}

源

您可以使用泛型和 LINQ 轻松地将其转换为更干净的代码：

private List<FieldInfo> GetConstants(Type type)
{
    FieldInfo[] fieldInfos = type.GetFields(BindingFlags.Public |
         BindingFlags.Static | BindingFlags.FlattenHierarchy);
    return fieldInfos.Where(fi => fi.IsLiteral && !fi.IsInitOnly).ToList();
}

或者用一行：

type.GetFields(BindingFlags.Public | BindingFlags.Static |
               BindingFlags.FlattenHierarchy)
    .Where(fi => fi.IsLiteral && !fi.IsInitOnly).ToList();

如果你想从目标类型中获取特定类型的所有常量的值，这里有一个扩展方法（扩展了本页上的一些答案）：

public static class TypeUtilities
{
    public static List<T> GetAllPublicConstantValues<T>(this Type type)
    {
        return type
            .GetFields(BindingFlags.Public | BindingFlags.Static | BindingFlags.FlattenHierarchy)
            .Where(fi => fi.IsLiteral && !fi.IsInitOnly && fi.FieldType == typeof(T))
            .Select(x => (T)x.GetRawConstantValue())
            .ToList();
    }
}

那么对于这样的课程

static class MyFruitKeys
{
    public const string Apple = "apple";
    public const string Plum = "plum";
    public const string Peach = "peach";
    public const int WillNotBeIncluded = -1;
}

您可以获取string常量值，如下所示：

List<string> result = typeof(MyFruitKeys).GetAllPublicConstantValues<string>();
//result[0] == "apple"
//result[1] == "plum"
//result[2] == "peach"

As Type 扩展：

public static class TypeExtensions
{
    public static IEnumerable<FieldInfo> GetConstants(this Type type)
    {
        var fieldInfos = type.GetFields(BindingFlags.Public | BindingFlags.Static | BindingFlags.FlattenHierarchy);
        return fieldInfos.Where(fi => fi.IsLiteral && !fi.IsInitOnly);
    }
    public static IEnumerable<T> GetConstantsValues<T>(this Type type) where T : class
    {
        var fieldInfos = GetConstants(type);
        return fieldInfos.Select(fi => fi.GetRawConstantValue() as T);
    }
}

使用 property.GetConstantValue() 获取值。

public class Constants
{
    public class InputType
    {
        public const string DOCUMENTPHOTO = "document-photo";
        public const string SELFIEPHOTO = "selfie-photo";
        public const string SELFIEVIDEO = "selfie-video";
        public static List<string> Domain { get { return typeof(Constants.InputType).GetAllPublicConstantValues<string>(); } }
    }
    public class Type
    {
        public const string DRIVINGLICENSE = "driving-license";
        public const string NATIONALID = "national-id";
        public const string PASSPORT = "passport";
        public const string PROOFOFRESIDENCY = "proof-of-residency";
        public static List<string> Domain { get { return typeof(Constants.Type).GetAllPublicConstantValues<string>(); } }
    }
    public class Page
    {
        public const string FRONT = "front";
        public const string BLACK = "back";
        public static List<string> Domain { get { return typeof(Constants.Page).GetAllPublicConstantValues<string>(); } }
    }
    public class FileType
    {
        public const string FRONT = "selfie";
        public const string BLACK = "video";
        public const string DOCUMENT = "document";
        public const string MEDIA = "media";
        public const string CAPTCHA = "captcha";
        public const string DIGITALSIGNATURE = "digitalSignature";
        public static List<string> Domain { get { return typeof(Constants.FileType).GetAllPublicConstantValues<string>(); } }
    }
}
public static class TypeUtilities
{
    public static List<T> GetAllPublicConstantValues<T>(this Type type)
    {
        return type
            .GetFields(BindingFlags.Public | BindingFlags.Static | BindingFlags.FlattenHierarchy)
            .Where(fi => fi.IsLiteral && !fi.IsInitOnly && fi.FieldType == typeof(T))
            .Select(x => (T)x.GetRawConstantValue())
            .ToList();
    }
}

使用： var inputTypeDomain = Constants.InputType.Domain;