使用仅在执行时已知的类型参数调用泛型方法 [英] Calling generic method with a type argument known only at execution time

问题描述

当然，我的真实代码看起来并不完全像这样.我试着写半伪代码来更清楚我想要做什么.

Of course my real code doesn't look exactly like this. I tried to write semi-pseudo code to make it more clear of whay I wanted to do.

看起来它只是把事情搞砸了.

Looks like it just messed things up instead.

所以，我真正想做的是:

So, what I actually would like to do is this:

Method<Interface1>();
Method<Interface2>();
Method<Interface3>();
...

嗯......我想也许我可以使用反射将它变成一个循环.所以问题是:我该怎么做.我非常对反射有很浅的了解.所以代码示例会很棒.

Well ... I thought that maybe I could turn it into a loop using reflection. So the question is: How how do I do it. I have very shallow knowledge of reflection. So code examples would be great.

场景如下:

public void Method<T>() where T : class
{}
public void AnotherMethod()
{
    Assembly assembly = Assembly.GetExecutingAssembly();

    var interfaces = from i in assembly.GetTypes()
    where i.Namespace == "MyNamespace.Interface" // only interfaces stored here
    select i;

    foreach(var i in interfaces)
    {
        Method<i>(); // Get compile error here!
    }

原帖:

嗨！

我正在尝试遍历命名空间中的所有接口，并将它们作为参数发送给这样的通用方法:

I'm trying to loop through all interfaces in a namespace and send them as arguments to a generic method like this:

public void Method<T>() where T : class
{}
public void AnotherMethod()
{
    Assembly assembly = Assembly.GetExecutingAssembly();

    var interfaces = from i in assembly.GetTypes()
    where i.Namespace == "MyNamespace.Interface" // only interfaces stored here
    select i;

    foreach(var interface in interfaces)
    {
        Method<interface>(); // Get compile error here!
    }
}

我得到的错误是需要类型名称，但找到局部变量名称".如果我尝试

The error I get is "Type name expected, but local variable name found". If I try

...
    foreach(var interface in interfaces)
    {
        Method<interface.MakeGenericType()>(); // Still get compile error here!
    }
}

我得到无法应用运算符‘<’到方法组"和System.Type"类型的操作数"关于如何解决这个问题的任何想法?

I get "Cannot apply operator '<' to operands of type 'method group' and 'System.Type'" Any idea on how to get around this problem?

推荐答案

好的，是时候编写一个简短但完整的程序了.基本答案和以前一样:

Okay, time for a short but complete program. The basic answer is as before:

• 使用 Type.GetMethod 查找打开"泛型方法
• 使用 MakeGenericMethod 使其通用
• 使用 Invoke 调用它

这是一些示例代码.请注意，我将查询表达式更改为点表示法 - 当您基本上只有一个 where 子句时，使用查询表达式是没有意义的.

Here's some sample code. Note that I changed the query expression to dot notation - there's no point in using a query expression when you've basically just got a where clause.

using System;
using System.Linq;
using System.Reflection;

namespace Interfaces
{
    interface IFoo {}
    interface IBar {}
    interface IBaz {}
}

public class Test
{
    public static void CallMe<T>()
    {
        Console.WriteLine("typeof(T): {0}", typeof(T));
    }

    static void Main()
    {
        MethodInfo method = typeof(Test).GetMethod("CallMe");

        var types = typeof(Test).Assembly.GetTypes()
                                .Where(t => t.Namespace == "Interfaces");

        foreach (Type type in types)
        {
            MethodInfo genericMethod = method.MakeGenericMethod(type);
            genericMethod.Invoke(null, null); // No target, no arguments
        }
    }
}

原答案

让我们先抛开调用变量接口"的明显问题.

Let's leave aside the obvious problems of calling a variable "interface" to start with.

你必须通过反射来调用它.泛型的重点是在编译时进行更多的类型检查.您在编译时不知道类型是什么 - 因此您必须使用泛型.

You have to call it by reflection. The point of generics is to put more type checking at compile time. You don't know what the type is at compile-time - therefore you've got to use generics.

获取泛型方法，并对其调用 MakeGenericMethod，然后调用它.

Get the generic method, and call MakeGenericMethod on it, then invoke it.

您的接口类型本身实际上是通用的吗?我问是因为你正在调用 MakeGenericType ，但没​​有传入任何类型参数......你是否试图调用

Is your interface type itself actually generic? I ask because you're calling MakeGenericType on it, but not passing in any type arguments... Are you trying to call

Method<MyNamespace.Interface<string>>(); // (Or whatever instead of string)

或

Method<MyNamespace.Interface>();

如果是后者，您只需要调用 MakeGenericMethod - 而不是 MakeGenericType.

If it's the latter, you only need a call to MakeGenericMethod - not MakeGenericType.

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