Question

I am working on an abstraction layer for making calls from JavaScript within a UIWebView into the native part of my application.

To that end I require a generic mechanism which translates a JavaScript function call into a Objective-C message to an object. This does work pretty well already, except for calling methods on Objective-C objects which require Block-Arguments.

How do I invoke such methods in a generic manner without having to pass NULL as block argument. I’d like to pass a generic block which can then iterate over all arguments passed into it (variable arguments).

To rephrase: Is there any way to generically call any methods with Block-Parameters notwithstanding the specific types of those blocks (i.e. differences in signatures) such that I can capture the arguments passed into those blocks when they are subsequently executed?

Answer 1

I haven’t tried exactly what you’re doing, but I think I know enough to say, unfortunately, “no”.

A couple problems are uniting against you here:

• Blocks are just blocks, and there’s no standard way to get a function pointer out of a block (it can be done, but not in a portable or future-proof way).
• Even if you had a function pointer, you couldn’t call it with a number of arguments determined at runtime, without using platform-specific assembly. C’s only support for this is using va_args.

(I hope I’m wrong about this and that someone will correct me, but I’m afraid I’m not.)