Re: Creating an NSInvocation from an NSMethodSignature
Re: Creating an NSInvocation from an NSMethodSignature
- Subject: Re: Creating an NSInvocation from an NSMethodSignature
- From: Michael Ash <email@hidden>
- Date: Tue, 12 May 2009 09:43:59 -0400
On Tue, May 12, 2009 at 8:50 AM, Mike Mangino
<email@hidden> wrote:
>
> On May 12, 2009, at 12:58 AM, Michael Ash wrote:
> [snip]
>
>>
>> My suggestion would be, if at all possible, avoid creating the
>> NSInvocation manually at all. By far the nicest way to create an
>> invocation is by capturing it using the -forwardInvocation: method.
>> That way you create it using the same syntax you use to send any other
>> message, and the runtime takes care of all the icky details like
>> argument sizes.
>
> I would love to do that. I'm trying to allow partial mocking of internal
> objects. The current code creates a partial mock as a proxy, which makes
> getting the invocation really easy. Unfortunately, it means you can't mock a
> method that is called inside the object.
>
> To work around this, I'm dynamically creating a subclass which overrides the
> methods I want to mock. This allows me to mock methods on calls to self.
> Unfortunately, I no longer get an NSInvocation.
>
> I was looking at removing all of the methods on the parent and handling them
> all with my own dispatch, but removing methods seems to be deprecated in
> 2.0. Can anyone think of another way to get an invocation?
>
> If not, I'll just build the table and parse things myself. I'll definitely
> skip structs.
This is actually surprisingly easy.
(Caveat: I have not actually done this.)
Use -methodForSelector: to get the IMP for a nonexistent method. This
IMP will be a function pointer straight to the runtime's forwarding
machinery. Then install that IMP as the implementation for your
overridden methods. Callers will go straight into the forwarding
machinery rather than into your overridden methods, which will then
invoke -forwardInvocation: as usual and you can then do as you like.
Since I haven't ever tried this, I'd be very interested to know how it
works for you if you try it.
Mike
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