Method Swizzle on iPhone device

Question

I tried both JRSwizzle, and MethodSwizzle. They compile fine on the simulator but throw a bunch of errors when I try to compile for Device (3.x)

Has anyone had any luck swizzling on the iphone? Whats the trick?

TIA

Answer 1

I have managed to swizzle some methods just by using the default objc functions for it.

IMP original = class_replaceMethod([SomeClass class], @selector(selector:), (IMP)function, "v@:");
class_addMethod([SomeClass class], @selector(anotherMethod:), original, "v@:");

This works flawlessly, both for the Simulator as the Device. You may want to take a look at the ObjCRuntime documentation for all other methods available.

If this does not work for you, please give us the errors you currently have.

Answer 2

The CocoaDev wiki has an extensive discussion on method swizzling here. Mike Ash has a relatively simple implementation at the bottom of that page:

#import <objc/runtime.h> 
#import <objc/message.h>
//....

void Swizzle(Class c, SEL orig, SEL new)
{
    Method origMethod = class_getInstanceMethod(c, orig);
    Method newMethod = class_getInstanceMethod(c, new);
    if(class_addMethod(c, orig, method_getImplementation(newMethod), method_getTypeEncoding(newMethod)))
        class_replaceMethod(c, new, method_getImplementation(origMethod), method_getTypeEncoding(origMethod));
    else
    method_exchangeImplementations(origMethod, newMethod);
}

I have not tested this, simply because I regard method swizzling as an extremely dangerous process and haven't had the need to use it yet.

Answer 3

Googling around a little bit I found a Version that

• works for Objective C 2 as well as earlier versions,
• allows swizzling class methods as well and
• all in all seems to be real code (from a working project) instead of just a snipplet.

Find it at the safariblock project on google code.