is it possible to compare a delegate?

General
1

I have a notification system in an app that I originally built using class interfaces. That has worked great forever but it has limitations. I wished to update the class to instead use a delegate so that I could create several different events going to different handlers. This also worked great after I wrapped my head around delegates which took some time :wink:

One function of the original class was to make sure that the original class wasn’t already subscribed to the specific event. I did this simply by just comparing the objects. If it was found then I wouldn’t add it again. This does not appear to work for delegates.

I am creating the delegate by the weakAddressOf command and storing it as a variant.

Just comparing the variants always returns false. 2 variants holding the same delegate, or at least the same method pointed to via the delegate. This makes sense I suppose since it’s 2 different creations of the delegate so they would not be the same.

Comparing the variant.hash doesn’t work for the same reason. Comparing the variant.objectValue doesn’t work either. What I really want to do is compare the address stored as the delegate, is that possible?

How can I compare 2 delegates to figure out if they point to the same method?

2

I tried a few things and got it to work by converting the Variants into Delegates and then converting the Delegates to Ptrs, and then comparing the pointer values directly:

[code]
Dim v1, v2 As Variant
v1 = WeakAddressOf Foo
v2 = WeakAddressOf Foo

Dim d1, d2 As MyDelegate
d1 = v1
d2 = v2

Dim p1, p2 As Ptr
p1 = d1
p2 = d2

If p1 = p2 Then MsgBox(“Same method”)[/code]

3

ah very good! I tried casting them to delegates( v) and that didn’t work at all, wouldn’t even compile as you can’t cast to a delegate. But I didn’t try just assigning them to ptr values. I will try that momentarily. Great idea!

4

What happens if two different objects register the same method?

5

then they would return true if they are the same. I can live with that. I need to be able to compare them so that you can deregister! That doesn’t work at the moment. I haven’t had a chance yet to experiment with Andrew’s implicit casting them to pointers yet. but if that works then problem solved.

6

and it looks like assigning the variants to the delegate first and then to a ptr makes it possible to compare them! Andrew, brilliant! I wouldn’t have believed you could do that if you couldn’t explicitly cast them that just assigning them to the variables already cast would do it but it works perfectly thank you!

7

Can you get the same result using CType?

8

It seems so:

[code] Dim v1, v2 As Variant
v1 = WeakAddressOf Foo
v2 = WeakAddressOf Foo

Dim p1, p2 As Ptr
p1 = CType(v1, MyDelegate)
p2 = CType(v2, MyDelegate)

If p1 = p2 Then MsgBox(“Same method”)
[/code]

9

I meant instead of using a variant.

  dim d1, d2 as mydelegate
  dim p1, p2 as ptr
  
  d1 = weakaddressof foo
  d2 = weakaddressof foo
  
  p1= ctype(d1, ptr)
  p2= ctype(d2, ptr)

  if p1 = p2 then