不使用 GetMethods 获取泛型方法 [英] Get a generic method without using GetMethods

问题描述

我想获取方法 System.Linq.Queryable.OrderyBy(IQueryable source, Expression> keySelector) 方法，但我一直在想空值.

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.

有没有人有任何见解?我不想循环遍历 GetMethods 结果.

Does anyone have any insight? I would prefer to not loop through the GetMethods result.

推荐答案

已解决(通过 hack LINQ)！

Solved (by hacking LINQ)!

我在研究同一问题时看到了您的问题.在没有找到好的解决方案后，我有了查看LINQ表达式树的想法.这是我想出的:

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

如果您在编译时不知道类型，这里是如何获取方法:

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;
}

务必将 typeof(Program) 替换为 typeof(WhateverClassYouDeclareTheseMethodsIn).

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

这篇关于不使用 GetMethods 获取泛型方法的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！