Question

我使用lambda表达式重构了List的通用CSV构建器以访问正确的值

public static string ToCsv<TModel>(this List<TModel> list, string delimiter, string lineBreak, string valueWrap, params Expression<Func<TModel, object>>[] expressions)
{
  var sb = new StringBuilder();

  var headers = expressions.Select(m => String.Format("{0}{1}{0}", valueWrap, GetPropertyName(m))).ToArray();
  sb.Append(String.Format("{0}{1}", String.Join(delimiter, headers), lineBreak));

  foreach (var listItem in list)
  {
    var values = expressions.Select(m => String.Format("{0}{1}{0}", valueWrap, m.Compile()(listItem))).ToArray();
    sb.Append(String.Format("{0}{1}", String.Join(delimiter, values), lineBreak));
  }

  return sb.ToString();
}

这很好用，但是因为我试图将它转移到几个服务器上的几个项目的公共代码中来访问。我无法引用System.Web.Mvc汇编

是否有一种访问DisplayName属性的好方法，如果不存在，请访问变量名称？

我当前的尝试访问((MemberExpression) expression.Body).Member.Name但是如果必须将值转换为字符串，它将无效。（即传递int并隐式转换）

迭代属性的第二次尝试不适用于内部类（即model =＆gt; model.innerClass.property）

Answer 1

使用几个简单的辅助函数，您可以消除对System.Web.Mvc程序集的所有引用。您还会在下面的示例中注意到（model =＆gt; model.member.property）有效。

using System;
using System.Collections.Generic;
using System.Text;
using System.Linq;
using System.Linq.Expressions;
using System.ComponentModel;
using System.Reflection;

namespace Test
{
    public class Program
    {
        public static void Main(string[] args)
        {
            List<Class1> foobars = new List<Class1>();
            foobars.Add(new Class1 { Foo = "Hello world!", Bar = -1, Skip = false, Ref = new Class2 { ToBe = true } });

            string result = foobars.ToCsv(",", Environment.NewLine, "\"", m => m.Foo, m => m.Bar, m => m.Ref.ToBe);
        }

        public class Class1
        {
            [DisplayName("Foo Property")]
            public string Foo { get; set; }

            public int Bar { get; set; }

            [DisplayName("Skipped Property")]
            public bool Skip { get; set; }

            [DisplayName("Reference")]
            public Class2 Ref { get; set; }
        }

        public class Class2
        {
            [DisplayName("To Be or Not To Be")]
            public bool ToBe { get; set; }
        }
    }

    public static class Extensions
    {
        public static string ToCsv<TModel>(this List<TModel> list, string delimiter, string lineBreak, string valueWrap, params Expression<Func<TModel, object>>[] expressions)
        {
            var sb = new StringBuilder();

            var headers = expressions.Select(m => String.Format("{0}{1}{0}", valueWrap, GetDisplayName(m))).ToArray();
            sb.Append(String.Format("{0}{1}", String.Join(delimiter, headers), lineBreak));

            foreach (var listItem in list)
            {
                var values = expressions.Select(m => String.Format("{0}{1}{0}", valueWrap, m.Compile()(listItem))).ToArray();
                sb.Append(String.Format("{0}{1}", String.Join(delimiter, values), lineBreak));
            }

            return sb.ToString();
        }

        // Get DisplayName, otherwise fallback to Name
        private static string GetDisplayName(LambdaExpression memberReference)
        {
            MemberInfo info = GetMemberInfo(memberReference);
            DisplayNameAttribute displayNameAttr = Attribute.GetCustomAttribute(info, typeof(DisplayNameAttribute)) as DisplayNameAttribute;
            return (displayNameAttr != null ? displayNameAttr.DisplayName : info.Name);
        }

        // Can be swapped for your favourite GetMemberInfo/GetPropertyInfo utility method (there are many out there)
        // Source: http://blog.baltrinic.com/software-development/dotnet/extension-methods-for-converting-lambda-expression-to-strings
        private static MemberInfo GetMemberInfo(LambdaExpression memberReference)
        {
            MemberExpression memberExpression;
            var unary = memberReference.Body as UnaryExpression;
            if (unary != null)
                //In this case the return type of the property was not object,
                //so .Net wrapped the expression inside of a unary Convert()
                //expression that casts it to type object. In this case, the
                //Operand of the Convert expression has the original expression.
                memberExpression = unary.Operand as MemberExpression;
            else
                //when the property is of type object the body itself is the
                //correct expression
                memberExpression = memberReference.Body as MemberExpression;

            if (memberExpression == null || !(memberExpression.Member is MemberInfo))
                throw new ArgumentException("Expression was not of the form 'x => x.member'.");

            return memberExpression.Member;
        }
    }
}

可以在不使用MVC的情况下访问DisplayName属性吗？

1 个答案: