Question

Supposed I have two objective-c classes, LBFoo and LBBar.

In LBFoo I have a method that looks like this:

- (void)doSomethingWithFoo:(NSNumber*)anArgument
{
  if(anArgument.intValue > 2)
    [LBBar doSomethingWithLBBar];
  else
    [LBBar doSomethingElseWithLBBar];
}

What I would like to do instead is pass an implementation to LBBar that was not declared ahead of time. (As in dynamically override an existing @selector within LBBar)

I know that an IMP type exists, is it possible to pass an IMP to a class in order to change its selector implementation.

Answer 1

you can use the method_setImplementation(Method method, IMP imp) function in objective-c runtime.

if you want to set an instance method, it would work something like this

method_setImplementation(class_getInstanceMethod([yourClass class], @selector(yourMethod)), yourIMP);

if you want a class method, just use class_getClassMethod instead of class_getInstanceMethod. The arguments should be the same.

that’s all there is to it. Note that IMP is just a void function pointer with the first 2 parameters being id self and SEL _cmd