找一个通用的方法，而无需使用的getMethods [英] Get a generic method without using GetMethods

问题描述

我想获得方法 System.Linq.Queryable.OrderyBy＆LT; T，TKEY的＆GT;（在IQueryable的＆LT; T＆GT;来源，例pression＆LT; Func键＆LT; T，TKEY的＆GT;＆GT;的KeySelectors ）的方法，但我一直想出空。

I want to get the method System.Linq.Queryable.OrderyBy<T, TKey>(the IQueryable<T> source, Expression<Func<T,TKey>> keySelector) method, but I keep coming up with nulls.

var type = typeof(T);
var propertyInfo = type.GetProperty(group.PropertyName);
var propertyType = propertyInfo.PropertyType;

var sorterType = typeof(Func<,>).MakeGenericType(type, propertyType);
var expressionType = typeof(Expression<>).MakeGenericType(sorterType);

var queryType = typeof(IQueryable<T>);

var orderBy = typeof(System.Linq.Queryable).GetMethod("OrderBy", new[] { queryType, expressionType }); /// is always null.

没有人有任何见解？我想preFER通过的getMethods 结果不循环。

推荐答案

解决（因黑客行为LINQ）！

Solved (by hacking LINQ)!

我看到你的问题，同时研究了同样的问题。发现没有很好的解决方案后，我有了主意，看看LINQ EX pression树。这就是我想出了：

I saw your question while researching the same problem. After finding no good solution, I had the idea to look at the LINQ expression tree. Here's what I came up with:

public static MethodInfo GetOrderByMethod<TElement, TSortKey>()
{
    Func<TElement, TSortKey> fakeKeySelector = element => default(TSortKey);

    Expression<Func<IEnumerable<TElement>, IOrderedEnumerable<TElement>>> lamda
        = list => list.OrderBy(fakeKeySelector);

    return (lamda.Body as MethodCallExpression).Method;
}

static void Main(string[] args)
{
    List<int> ints = new List<int>() { 9, 10, 3 };
    MethodInfo mi = GetOrderByMethod<int, string>();           
    Func<int,string> keySelector = i => i.ToString();
    IEnumerable<int> sortedList = mi.Invoke(null, new object[] { ints, 
                                                                 keySelector }
                                           ) as IEnumerable<int>;

    foreach (int i in sortedList)
    {
        Console.WriteLine(i);
    }
}

输出：10 3 9

output: 10 3 9

编辑：这里是如何获得的方法，如果你不知道在编译时的类型：

Here is how to get the method if you don't know the type at compile-time:

public static MethodInfo GetOrderByMethod(Type elementType, Type sortKeyType)
{
    MethodInfo mi = typeof(Program).GetMethod("GetOrderByMethod", Type.EmptyTypes);

    var getOrderByMethod = mi.MakeGenericMethod(new Type[] { elementType,
                                                             sortKeyType });
    return getOrderByMethod.Invoke(null, new object[] { }) as MethodInfo;
}

请务必更换的typeof（节目）用typeof（WhateverClassYouDeclareTheseMethodsIn）。

Be sure to replace typeof(Program) with typeof(WhateverClassYouDeclareTheseMethodsIn).

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