Expression.Lambda Generics中的非特定类型

Question

以下代码工作正常(它构建一个通用的OrderBy):

public class Item
{
    public int Value { get; set; }
    public string Name { get; set; }
}

var _List = new List<Item>
{
    new Item{ Name = "Smith", Value = 3},
    new Item{ Name = "Smith", Value = 2},
    new Item{ Name = "Wesson", Value = 1},
    new Item{ Name = "Wesson", Value = 4},
}.AsQueryable<Item>();

var _Type = typeof(Item);

// OrderBy
var _OrderByProperty = _Type.GetProperty("Value");
var _OrderByParameter = Expression.Parameter(typeof(Item), "x");
// OrderBy(x => x.Value)
var _OrderByBody = Expression.Property(_OrderByParameter, _OrderByProperty.Name);
var _OrderByLambda = Expression.Lambda<Func<Item, Int32>>
    (_OrderByBody, _OrderByParameter);
// apply the OrderBy
_List = _List.OrderBy(_OrderByLambda);

但是,我想以这种方式改变这一行:

var _OrderByLambda = Expression.Lambda<Func<Item, object>>
    (_OrderByBody, _OrderByParameter);

这样的更改将使有序列的数据类型通用.但是,这样的更改会导致以下异常:

类型'System.Int32'的表达式不能用于返回类型'System.Object'

有任何想法吗？

编辑,谢谢你的答案,这很好用:

var _OrderByProperty = _Type.GetProperty("Value");
var _OrderByParameter = Expression.Parameter(typeof(Item), "x");
// OrderBy(x => x.Value)
var _OrderByBody = Expression.Property(_OrderByParameter, _OrderByProperty.Name);
var _OrderByConverted = Expression.Convert(_OrderByBody, typeof(object));
var _OrderByLambda = Expression.Lambda<Func<Item, object>>
    (_OrderByConverted, _OrderByParameter);
// apply the OrderBy
_List = _List.OrderBy(_OrderByLambda);

Answer 1

您需要指定正文的返回类型System.Object.您可以通过插入转换(C#隐式执行)来完成此操作:

_OrderByBody = Expression.Convert(_OrderByBody, typeof(object));