Passing a delegate as an Attribute

Question

I'm trying to use this method to pass a delegate as a parameter.

public delegate Guid SpaceIdGetter();
public class SpaceIdAttribute : Attribute
    {
        public SpaceIdGetter spaceGetter { get; set; }

        public SpaceIdAttribute(Type delegateType, string delegateName)
        {
            spaceGetter = (SpaceIdGetter)Delegate.CreateDelegate(delegateType, delegateType.GetMethod(delegateName));
        }
    }

    public static class ContextInfo
    {
        public static SpaceIdGetter GetSpaceId()
        {
            return new SpaceIdGetter( () =>
                    {
                        return Guid.Empty;
                    }
                );
        }
    }

I'm getting an error when I try to create the delegate with reflection

spaceGetter = (SpaceIdGetter)Delegate.CreateDelegate(delegateType, delegateType.GetMethod(delegateName));

Type must derive from Delegate.

Edit: here's how I'm using it

[SpaceId(typeof(ContextInfo), "GetSpaceId")]
public virtual string Body { get; set; }

In `c# 6.0` you can use `nameof(GetSpaceId)` instead of string. — Sinatr, Aug 06 '15 at 08:46

score 2 · Accepted Answer · answered Aug 06 '15 at 08:52

The ContextInfo is actually a factory already creating the delegate type - so no need to create delegate via reflection - you just have to call the factory via reflection:

public SpaceIdAttribute(Type delegateType, string delegateName)
{
  var factoryMethod = delegateType.GetMethod(delegateName);
  spaceGetter = (SpaceIdGetter)factoryMethod.Invoke(null, null);
}

score 0 · Answer 2 · answered Aug 06 '15 at 08:49

0

ContextInfo is not a Delegate and Delegate.CreateDelegate must take a delegate. Try: spaceGetter = (SpaceIdGetter)Delegate.CreateDelegate(typeof(Action<Guid>), delegateType.GetMethod(delegateName));

answered Aug 06 '15 at 08:49

Arnon Axelrod

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Getting this now: Cannot bind to the target method because its signature or security transparency is not compatible with that of the delegate type. – Adrian Buzea Aug 06 '15 at 08:52

Passing a delegate as an Attribute

2 Answers2