C# 使用表达式树获取特性的值

一、定义特性

/// <summary>
/// 定义特性
/// </summary>
[AttributeUsage(AttributeTargets.Field | AttributeTargets.Class | AttributeTargets.Property, AllowMultiple = false)]
public class DataMember : Attribute
{
    public string Name { get; set; }

    public string Type { get; set; }

}

二、创建工具类

　　利用泛型类得知要获取那个类上成员特性的类型，这样就能用Lambda表达式了。Expression.Body读取时是 System.Linq.Expressions.PropertyExpression 类型，找不到断点中Member属性。所以需要转换成 System.Linq.Expressions.MemberExpression 类型

/// <summary>
/// 获取特性工具类
/// </summary>
/// <typeparam name="T"></typeparam>
public static class AttrTool<T>
{
    /// <summary>
    /// 获取特性Name属性
    /// </summary>
    /// <typeparam name="Result"></typeparam>
    /// <param name="expression"></param>
    /// <returns></returns>
    public static string DataMemberName<Result>(Expression<Func<T, Result>> expression)
    {
        var body = expression.Body as MemberExpression;
        var attr = body.Member.CustomAttributes.FirstOrDefault(t => t.AttributeType == typeof(DataMember));
        var property = attr.NamedArguments.FirstOrDefault(t => t.MemberName == "Name");
        return property.TypedValue.Value.ToString();
    }
    /// <summary>
    /// 获取特性Type属性
    /// </summary>
    /// <typeparam name="Result"></typeparam>
    /// <param name="expression"></param>
    /// <returns></returns>
    public static string DataMemberType<Result>(Expression<Func<T, Result>> expression)
    {
        var body = expression.Body as MemberExpression;
        var attr = body.Member.CustomAttributes.FirstOrDefault(t => t.AttributeType == typeof(DataMember));
        var property = attr.NamedArguments.FirstOrDefault(t => t.MemberName == "Type");
        return property.TypedValue.Value.ToString();
    }

}

三、定义测试模型及调用

class Program
{

    static void Main(string[] args)
    {

        var temp = AttrTool<AttrModel>.DataMemberName(t => t.Name);
        Console.WriteLine();
    }
}

/// <summary>
/// 测试模型
/// </summary>
public class AttrModel
{
    [DataMember(Name = "this is Test", Type = "string")]
    public string Name { get; set; }
}