如何通过使用lambda表达式作为参数进行反射来调用方法？ [英] How do I invoke a method through reflection with a lambda expression as a parameter?

问题描述

  MethodInfo m = myList.GetType（）。GetMethod（ConvertAll，System。 Reflection.BindingFlags.InvokeMethod）.MakeGenericMethod（typeof运算（目标））; 
列表< object> myConvertedList =（List< object>）m.Invoke（myList，new object [] {（t =>（object）t）}）; 
  

myList是特定类型（应用程序未知）的通用列表，我想转换它到一个对象列表来做一些操作。

然而，这个失败与此错误：不能将lambda表达式转换为键入'object'，因为它不是委托类型

你能帮我找到问题吗？我试图做一些不可能的事情吗？

是否有其他方法可以实现同样的目的？

解决方案

lambda表达式可以转换为具有正确签名的委托类型或表达式树 - 但您需要指定它是哪种委托类型。

我认为你的代码会更简单，如果你把它作为一个通用的方法：

  public static List< object> ConvertToListOfObjects< T>（List< T>列表）
 {
 return list.ConvertAll< object>（t => t）; 
} 
  

然后你只需要找到并调用即可方法一般：

$ p $ MethodInfo method = typeof（Foo）.GetMethod（ConvertToListOfObjects，
BindingFlags.Static | BindingFlags 。上市）;
类型listType = list.GetType（）。GetGenericArguments（）[0];
MethodInfo concrete = method.MakeGenericMethod（new [] {listType}）;
列表< object> objectList =（List< object>）concrete.Invoke（null，
new object [] {list}）;


完整示例：

 使用系统; 
使用System.Reflection; 
使用System.Collections.Generic; 
 
 class Test 
 {
 public static List< object> ConvertToListOfObjects< T>（List< T>列表）
 {
 return list.ConvertAll< object>（t => t）; 
} 
 
 static void Main（）
 {
 object list = new List< int> {1，2，3，4}; 
 
 MethodInfo method = typeof（Test）.GetMethod（ConvertToListOfObjects，
 BindingFlags.Static | BindingFlags.Public）; 
类型listType = list.GetType（）。GetGenericArguments（）[0]; 
 MethodInfo concrete = method.MakeGenericMethod（new [] {listType}）; 
列表< object> objectList =（List< object>）concrete.Invoke（null，
 new object [] {list}）; 
 
 foreach（objectList中的对象）
 {
 Console.WriteLine（o）; 
} 
} 
} 
  

I want to do this:

MethodInfo m = myList.GetType().GetMethod("ConvertAll", System.Reflection.BindingFlags.InvokeMethod).MakeGenericMethod(typeof(object));
List<object> myConvertedList = (List<object>)m.Invoke(myList, new object[]{ (t => (object)t)});

myList is a generic list of a specific type (unknown to the application), and I want to convert it to a list of objects to do some operations.

However this fails with this error: "Cannot convert lambda expression to type 'object' because it is not a delegate type"

Can you help me find what's wrong? Am I trying to do something that's not possible?

Is there some other way to achieve the same thing?

解决方案

A lambda expression is convertible to either a delegate type or an expression tree with the right signature - but you need to specify which delegate type it is.

I think your code would be much simpler if you made this a generic method:

public static List<object> ConvertToListOfObjects<T>(List<T> list)
{
    return list.ConvertAll<object>(t => t);
}

Then you just need to find and invoke that method generically:

MethodInfo method = typeof(Foo).GetMethod("ConvertToListOfObjects",
    BindingFlags.Static | BindingFlags.Public);
Type listType = list.GetType().GetGenericArguments()[0];
MethodInfo concrete = method.MakeGenericMethod(new [] { listType });
List<object> objectList = (List<object>) concrete.Invoke(null, 
                                                   new object[]{list});

Complete example:

using System;
using System.Reflection;
using System.Collections.Generic;

class Test
{
    public static List<object> ConvertToListOfObjects<T>(List<T> list)
    {
        return list.ConvertAll<object>(t => t);
    }

    static void Main()
    {
        object list = new List<int> { 1, 2, 3, 4 };

        MethodInfo method = typeof(Test).GetMethod("ConvertToListOfObjects",
            BindingFlags.Static | BindingFlags.Public);
        Type listType = list.GetType().GetGenericArguments()[0];
        MethodInfo concrete = method.MakeGenericMethod(new [] { listType });
        List<object> objectList = (List<object>) concrete.Invoke(null,
                                                    new object[] {list});

        foreach (object o in objectList)
        {
            Console.WriteLine(o);
        }
    }
}

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