如何从被调用的方法实现创建NSInvocation？

Question

I have a function that looks like this:

void myMethodImpl(id self, SEL _cmd, ...)

I use this as a implementation for a method on a class

class_addMethod(aClass, aSelector, (IMP)myMethodImpl, types);

so myMethodImpl get's called when a message is sent to aClass with selector aSelector. Now there I'd like to create an NSInvocation with all parameters from myMethodImpl .

Is there an easy way to create a NSInvocation from the parameter list or do I have to check every element for it's type and add it accordingly?

Answer 1

Since you're adding a method to the class, why not add/swizzle forwardInvocation: instead? At that point the runtime will have nicely built an invocation for you.

Answer 2

This is not possible. A simple google search shows this article:

http://www.wincent.com/a/about/wincent/weblog/archives/2006/03/nsinvocation_an.php

Which clearly explains how va_args don't properly work with NSInvocation.

Answer 3

It is possible, indeed. Have a look to the actionSelectorImplementation function in https://github.com/rlopezdiez/TMInstanceMethodSwizzler/blob/master/Classes/TMInstanceMethodSwizzler.m