C# 使用表達式樹獲取特性的值

一、定義特性

/// <summary>
/// 定義特性
/// </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、創建工具類

　　利用泛型類得知要獲取那個類上成員特性的類型，這樣就能用Lambda表達式了。Expression.Body讀取時是 System.Linq.Expressions.PropertyExpression 類型，找不到斷點中Member屬性。所以需要轉換成 System.Linq.Expressions.MemberExpression 類型

/// <summary>
/// 獲取特性工具類
/// </summary>
/// <typeparam name="T"></typeparam>
public static class AttrTool<T>
{
    /// <summary>
    /// 獲取特性Name屬性
    /// </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>
    /// 獲取特性Type屬性
    /// </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、定義測試模型及調用

class Program
{

    static void Main(string[] args)
    {

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

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