您可以将枚举值分配给 C# 中的枚举吗[关闭]

Question

我想为名称列表创建一个枚举，并为名称所属的类别列表创建另一个枚举。我看到了这篇出色的帖子here，它在将字符串分配给枚举方面做得很好，但我想要做的类似于以下内容：

public enum Name
{
    [CategoryAttribute(Category.Category1)]
    Name1,
    [CategoryAttribute(Category.Category2)]
    Name2,
    [CategoryAttribute(Category.Category3)]
    Name3
}

public enum Category
{
    Category1,
    Category2,
    Category3
}

然后我会使用他们在我上面提到的帖子中创建的扩展来查找当前名称的类别等。有没有办法在 C# 中做到这一点？

Answer 1

Name Enum 有名字，Name4 是一个没有类别属性的成员示例

public enum Name
{
    [Category(Category.Category1)]
    Name1,
    [Category(Category.Category2)]
    Name2,
    [Category(Category.Category3)]
    Name3,
    Name4
}

public enum Category
{
    //default value to return from GetCategory if no Category is assigned
    None,

    Category1,
    Category2,
    Category3
}

public class CategoryAttribute : Attribute
{
    public Category Category { get; set; }

    public CategoryAttribute(Category cat)
    {
        Category = cat;
    }
}

e 参数中传递的值是枚举的底层类型的值，在本例中为 int。为了获取分配的属性，我们首先需要获取与 int 关联的名称，然后使用该名称搜索属性。

public static class NameMethods
{
    public static Category GetCategory(this Name e)
    {
        var name = Enum.GetName(typeof(Name), e);
        var  member = e.GetType().GetMember(name).FirstOrDefault();
        var attr = Attribute.GetCustomAttribute(member, typeof(CategoryAttribute)) as CategoryAttribute;

        return attr?.Category ?? Category.None;
    }
}

使用四种不同的类别运行代码

public static class Program
{
    static void Main(string[] args)
    {
        var result = Name.Name1.GetCategory(); //Category1
        var result1 = Name.Name2.GetCategory(); //Category2
        var result2 = Name.Name3.GetCategory(); //Category3
        var result3 = Name.Name4.GetCategory(); //None
    }
}

如果您想反其道而行之，获取已分配给特定类别的名称列表，则可以使用此方法。请注意，此代码只允许为每个名称分配一个类别。

public static List<Name> GetNames(Category category)
{
    //Find all Members of Name Enum Type that have a categoryAttribute with the Category property assigned to the category parameter.
    var members = typeof(Name).GetMembers().ToList();
    var result = new List<Name>();
    foreach (var member in members)
    {
        //get attributes for member
        var categoryAttribute = Attribute.GetCustomAttribute(member, typeof(CategoryAttribute)) as CategoryAttribute;
        if (categoryAttribute != null && categoryAttribute.Category == category)
        {
            //use the member name to get an instance of enumerated type.
            Enum.TryParse(member.Name, out Name name);
            result.Add(name);
        }
    }

    return result;
}

Answer 2

当您创建自己的属性时，您可以传递Category enum 本身，而不是传递字符串。请参阅下面的实现：

public enum Category
{
    Category1,
    Category2,
    Category3
}

public enum Name
{
    [Category(Category.Category1)]
    Name1,

    [Category(Category.Category2)]
    Name2,

    [Category(Category.Category3)]
    Name3
}

public class CategoryAttribute : Attribute
{
    public Category category;

    public CategoryAttribute(Category category)
    {
        this.category = category;
    }
}

public static class Extentions
{
    public static Category GetCategory(this Name obj)
    {
        var type = obj.GetType();
        var attr = (CategoryAttribute) Attribute.GetCustomAttribute(type.GetType(), typeof(CategoryAttribute));
        return attr.category;
    }
}

Answer 3

稍加注意，你可以给每个枚举的整数值一个特定的含义；

public enum Name
{
    // Category 1
    Name1 = (int)Category.Category1,
    Name2,
    Name3,

    // Category 2
    Name4 = (int)Category.Category2,
    ...
}

public enum Category {
    Category1 = 1000,
    Category2 = 2000,
}

public Category GetCategory(Name name) => (Category)((int)name - ((int)name % 1000));