C# Attribute

Remark特性的应用场景

场景一：用户状态的枚举值，定义的是英文的字段，需要输出中文含义。枚举定义如下：

public enum UserState
{
    /// <summary>
    /// 正常
    /// </summary>
    Normal = 0,

    /// <summary>
    /// 冻结
    /// </summary>
    Frozen = 1,

    /// <summary>
    /// 删除
    /// </summary>
    Deleted = 2
}

普通做法：根据枚举值进行判断，然后输出中文含义：

UserState userState = UserState.Normal;
switch (userState)
{
    case UserState.Deleted:
    Console.WriteLine("删除");
    break;

    case UserState.Normal:
    Console.WriteLine("正常");
    break;

    case UserState.Frozen:
    Console.WriteLine("冻结");
    break;
}

这种写法违反开闭原则，不利于以后的扩展，下面使用特性实现

先定义Remark特性：

/// <summary>
/// Remark特性
/// </summary>
public class RemarkAttribute : Attribute
{
    private string _Remark;

    /// <summary>
    /// 有参构造函数
    /// </summary>
    /// <param name="remark"></param>
    public RemarkAttribute(string remark)
    {
        _Remark = remark;
    }

    /// <summary>
    /// 获取Remark
    /// </summary>
    /// <returns></returns>
    public string GetRemark()
    {
        return _Remark;
    }
}

UserState枚举修改如下：

public enum UserState
{
    /// <summary>
    /// 正常
    /// </summary>
    [Remark("正常")]
    Normal = 0,

    /// <summary>
    /// 冻结
    /// </summary>
    [Remark("冻结")]
    Frozen = 1,

    /// <summary>
    /// 删除
    /// </summary>
    [Remark("删除")]
    Deleted = 2
}

写一个扩展方法，对Enum类型进行扩展：

public static class RemarkExtension
{
    /// <summary>
    /// Enum的扩展方法
    /// </summary>
    /// <param name="value"></param>
    /// <returns></returns>
    public static string GetRemark(this Enum value)
    {
        //获取类型
        Type type = value.GetType();

        //获取字段
        FieldInfo fieId = type.GetField(value.ToString());

        //判断字段上面是否定义了ReamrkAttribute特性
        if (fieId.IsDefined(typeof(RemarkAttribute)))
        {
            //创建实例
            RemarkAttribute attribute = (RemarkAttribute)fieId.GetCustomAttribute(typeof(RemarkAttribute));

            return attribute.GetRemark();
        }
        else
        {
            return value.ToString();
        }
    }
}

最后Main()方法里面调用

static void Main(string[] args)
{
    UserState userState = UserState.Normal;
    Console.WriteLine(userState.GetRemark());
    Console.ReadKey();
}

输出结果