使用动态泛型类型参数创建泛型类的实例 [英] Create instance of generic class with dynamic generic type parameter

问题描述

我需要创建一个通用类的实例，如下所示：

I need to create instance of a generic class like this:

 Type T = Type.GetType(className).GetMethod(functionName).ReturnType;
 var comparer = new MyComparer<T>(); // ERROR: "The type or namespace name 'T' could not be found"

我发现了这个答案，其中只有通过反射才能实现。但是使用反射，我得到了需要转换为通用类型的对象。我这样尝试过

I found this answer where this is possible only with reflection. But using reflection I get object which I need to cast to my generic type. I tried like this

 Type myGeneric = typeof(MyComparer<>);
 Type constructedClass = myGeneric.MakeGenericType();
 object created = Activator.CreateInstance(constructedClass);
 var comparer = (T)Convert.ChangeType(created, T);// ERROR: "The type or namespace name 'T' could not be found"

，但得到相同的错误。

but get the same error. How to solve it?

这里是一个完整的示例：

Here is a complete example:

    public static bool Test(string className, string functionName, object[] parameters, object correctResult)
    {
        var method = Type.GetType(className).GetMethod(functionName);
        Type T = method.ReturnType;
        var myResult = method.Invoke(null, parameters);
        dynamic myResultAsT = Convert.ChangeType(myResult, T);
        dynamic correctResultAsT = Convert.ChangeType(correctResult, T);
        var comparer = new MyComparer<T>();    // Problem is here!!!       
        return comparer.Equals(myResultAsT, correctResultAsT);            
    }

这个想法是进行单元测试，该测试将调用带有参数和将其结果与正确的结果进行比较。但是我需要自定义比较器，因此我实现了 MyComparer ，由于编译器错误而无法使用。

The idea is to make a unit test which will call a function with parameters and compare its result with the correct result. But I need custom comparer, so I implement MyComparer which I cannot use because of a compiler error.

public class MyComparer<T> : IEqualityComparer<T>
{
    public bool Equals(T x, T y){/* some implementation*/}
}

推荐答案

我找到了非常简单的问题解决方案。无需将对象强制转换为特定类型 T ，只需使用 dynamic 关键字而不是强制转换

I found very simple solution to problem. There is no need to cast object to specific type T, just use dynamic keyword instead of casting

   Type myGeneric = typeof(MyComparer<>);
   Type constructedClass = myGeneric.MakeGenericType(T);
   object created = Activator.CreateInstance(constructedClass);
   dynamic comparer = created; // No need to cast created object to T

然后可以正常使用比较器来调用其方法像这样：

and then I can use comparer normally to call its methods like:

   return comparer.Equals(myResultAsT, correctResultAsT);

根据 LueTm 注释，可能可以再次使用反射并调用比较器方法，但是此解决方案看起来容易得多。

According to LueTm comments, it is probably possible to use reflection again and call comparer methods, but this solution looks much easier.

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