Reputation: 12624
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?
Upvotes: 17
Views: 8768
Reputation: 827
I use this with generics in EF Core including making Expression<Func<SomeModelType,bool>> for let's say a Where clause, you can chain MakeGenericType calls with nested generics.
var someType = SomeDbContext.SomeDataModelExample.GetType();
var funcType1 = typeof(Func<>).MakeGenericType(new Type[] { someType });
var result = Activator.CreateInstance(funcType1);
var result2 = Activator.CreateInstance(funcType1, someParams);
Upvotes: 1
Reputation: 9891
you could create Expression objects instead of a func, and compile() the expression to get a Func delegate.
Upvotes: 0
Reputation: 1064094
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.
Upvotes: 30
Reputation: 116744
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.
Upvotes: 0