I need to implement the method:
object GetFactory(Type type);
This method needs to return a Func<T> where typeparam 'T' is the 'type'.
So, my problem is that I don't know how to create a Func<?> at runtime using reflection. Activator.CreateInstance doesn't work because there are no constructors on delegates.
Any Ideas?
You use Delegate.CreateDelegate
, i.e. from a MethodInfo
; below, I've hard-coded, but you would use some logic, or Expression
, to get the actual creation method:
using System;
using System.Reflection;
class Foo {}
static class Program
{
static Func<T> GetFactory<T>()
{
return (Func<T>)GetFactory(typeof(T));
}
static object GetFactory(Type type)
{
Type funcType = typeof(Func<>).MakeGenericType(type);
MethodInfo method = typeof(Program).GetMethod("CreateFoo",
BindingFlags.NonPublic | BindingFlags.Static);
return Delegate.CreateDelegate(funcType, method);
}
static Foo CreateFoo() { return new Foo(); }
static void Main()
{
Func<Foo> factory = GetFactory<Foo>();
Foo foo = factory();
}
}
For non-static methods, there is an overload of Delegate.CreateDelegate
that accepts the target instance.
I think the usual approach would be to make the "dumb" version be the thing that you spoof at runtme, and then provide a helper extension method to provide the type-safe version on top of it.
you could create Expression objects instead of a func, and compile() the expression to get a Func delegate.
来源:https://stackoverflow.com/questions/658316/runtime-creation-of-generic-funct