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; }

}