如何创建功能以编程方式委托 [英] How to create a Func<> delegate programmatically

问题描述

我有一个小的依赖项注入框架，并且我试图使它动态地解析Lazy<>实例.想法是做这样的事情:

I have a small dependency injection framework, and I am trying to make it resolve Lazy<> instances dynamically. The idea is to do something like that:

DIContainer.Register<IDbCommand,SqlCommand>();

var lazyCommand = DIContainer.Resolve<Lazy<IDbCommand>>();

前几天，我读到Autofac能够做到这一点.

I read the other day that Autofac was able of doing that.

我一直在尝试为该Lazy<>实例设置构造函数.在下一个测试代码中，抛出异常，因为所需的类型构造函数期望Func<arg>，但是我传递了Func<Object>:

I am stuck trying to set the constructor for that Lazy<> instance. In the next test code, a exception is thrown because the desired type constructor is expecting a Func<arg>, but I am passing a Func<Object>:

    static readonly Type _lazyType = typeof(Lazy<>);
    static Object ResolveTest(Type type)
    {
        if (type.IsGenericType && type.GetGenericTypeDefinition() == _lazyType)
        {
            var arg = type.GetGenericArguments()[0];

            return Activator.CreateInstance(_lazyType.MakeGenericType(arg), new Func<Object>(() => ResolveType(arg)));
        }
        else 
            return ResolveType(type);
    }

我不知道如何创建适合Lazy<>构造函数参数的委托.有什么主意吗?

I am out of ideas about how to create a delegate that fits for the Lazy<> constructor parameter. Any idea?

干杯.

推荐答案

那不是小事.一种可能的解决方案是使用反射:

That's not trivial. One possible solution would be to work with reflection:

1. 创建通用的ResolveType方法:

public static T ResolveType<T>()
{
    return (T)ResolveType(typeof(T));
}

创建使用此方法的委托:

Create a delegate that uses this method:

// You probably want to cache this MethodInfo:
var method = typeof(TypeContainingResolveType)
                 .GetMethods()
                 .Single(x => x.IsGenericMethod && 
                              x.Name == "ResolveType")
                 .MakeGenericMethod(arg);

var delegate = Delegate.CreateDelegate(
                   typeof(Func<>).MakeGenericType(arg),
                   method);

使用该代表:

Use that delegate:

return Activator.CreateInstance(_lazyType.MakeGenericType(arg), delegate);

这篇关于如何创建功能以编程方式委托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！