创建动态泛型类型参数

Question

泛型类的实例，我需要这样的创建一个通用类的实例：

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

我发现这个answer哪里，这是可能仅与反思。但使用反射我得到的对象，我需要投给我的泛型类型。我试过像这样

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" 

但是得到相同的错误。如何解决它？

下面是一个完整的例子：

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);    
    } 

的想法是做一个单元测试，它将调用带有参数的功能，并将其结果与正确结果进行比较。但我需要自定义比较器，所以我实现MyComparer，由于编译器错误，我无法使用它。

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

Answer 1

我觉得很简单的解决问题。有没有必要投object到特定类型的T，只是使用dynamic关键字，而不是铸造

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 

，然后我可以用比较器通常调用它的方法，如：

return comparer.Equals(myResultAsT, correctResultAsT); 

据LueTm评论，可能再次使用反射并调用比较器方法，但这种解决方案看起来更容易。

Answer 2

看起来你几乎没有：

// t is a variable, so make it lowercase. This is where some of the confusion comes from 
Type t = Type.GetType(className).GetMethod(functionName).ReturnType; 
Type myGeneric = typeof(IEqualityComparer<>); 

// You need to provide the generic type to make it generic with 
// You want IEqualityComparer<T>, so: 
Type constructedClass = myGeneric.MakeGenericType(t); 

// Now create the object 
object created = Activator.CreateInstance(constructedClass); 

// This is tricky without more context... 
// You could try this, but to tell you more I would need to know where you use 
// the comparer instance. Are you using it in a LINQ query, or in a Sort()? 
// If so just cast it to a IEqualityComparer<YourType>, and 
// make YourType whaterver you need it to be in the list or the query... 
var comparer = (IEqualityComparer<object>)created;