Accepting mouse scroll gestures in wxPython on Mac OS X

Question

On Mac OS X the trackpad has support for several gestures, one is the two fingered swipe to scroll up, down, left, or right on a page. wxPython has a panel to help create scrolled widgets wx.lib.scrolledpanel. However it does not have support for gestures which is a real pain.

I have tried to modify the NSView, as it is done if it were a normal Objective C application, however the NSEvents use methods (touchesBeganWithEvent:, etc) that are subclassed to be used as a notification and handling of an event. This is unlike the Bind calls in wxPython. This would be fine however if Objective C allowed monkey patching... eg

def handleTouchBegin(event):
    print "Hey a touch event has begun!"

view.touchBeganWithEvent_ = handleTouchBegin

but as you can guess PyObj C errors (because Objective C doesn't support monkey patching or not in any clean and nice fashion) and I get the following error

TypeError: cannot change a method

Ok well I could do what apple says and subclass it, but the object is already created, so how can I still capture the events. Of course there is also

NSEvent addGlobalMonitorForEventsMatchingMask: 
and
NSEvent addLocalMonitorForEventsMatchingMask: 

but those also disappoint in that they either don't even deal with the application (global deals with all the others) or doesn't deal with a single NSView's events (or does it and I am misinformed).

So how should I do this? Am I missing another option, I know I read something about NSResponder but from what I gathered that is what NSView is, an event responder and you don't add one to a NSView.

Are there observers like in QTKit such as for monitoring the load state changing ( https://developer.apple.com/library/mac/documentation/Cocoa/Conceptual/QTKitApplicationProgrammingGuide/AnatomyoftheQTKFramework/AnatomyoftheQTKFramework.html#//apple_ref/doc/uid/TP40008156-CH109-SW11 )?

Answer 1

ObjC doesn't support Python-style monkeypatching… but it does support some similar features like method swizzling, class posing, category interposition, etc. And PyObjC can do all of those things.

Off the top of my head, swizzling from PyObjC should look something like this:

def swizzle(cls, sel, func):
    oldimp = cls.instanceMethodForSelector_(sel)
    def wrapper(self, *args, **kwargs):
        return func(self, oldimp, *args, **kwargs)
    newmethod = objc.selector(wrapper, 
                              selector=oldimp.selector, signature=oldimp.signature)
    objc.classAddMethod(cls, sel, newmethod)
    return wrapper