Unable to use ObjCBlock in pythonista3.4

[shinyformica]

Hey all you pythonistas, it's been a while.

Super super excited about the new version of Pythonista!
I'm converting the big project we have which was written in python2/pythonista3.3 to be python3/pythonista3.4, and I ran into one major issue: I'm getting crashes if I try to use ObjCBlocks in pythonista3.4 which worked fine in pythonista3.3.

Here's the main example, pulled from a much more complex chunk of code, of a custom sheet presentation controller, which is supposed to be able to call a completion function via a block:

import objc_util
import ui

UIViewController = objc_util.ObjCClass("UIViewController")
UIView = objc_util.ObjCClass("UIView")
UIModalPresentationFormSheet = 2
UIModalTransitionStyleCoverVertical = 0

def getRootUIViewController():
    app = objc_util.UIApplication.sharedApplication()
    window = app.delegate().window()
    if not window: return None
    return window.rootViewController()

def getUIViewController(view):
    #### If the view is a standard pythonista ui.View, we can
    #### try to directly retrieve the view controller
    SUIView = objc_util.ObjCClass('SUIView')
    SUIViewController = objc_util.ObjCClass('SUIViewController')
    UIView = objc_util.ObjCClass('UIView')
    UIViewController = objc_util.ObjCClass('UIViewController')

    if isinstance(view, ui.View):
        viewobj = view.objc_instance
        vc = SUIViewController.viewControllerForView_(viewobj)
        if vc is not None: return vc
    elif isinstance(view, objc_util.ObjCInstance) and \
            view.isKindOfClass_(SUIView):
        viewobj = view
        vc = SUIViewController.viewControllerForView_(viewobj)
        if vc is not None: return vc
    #### Otherwise we have to search the "responder chain"
    #### for the first instance of a UIViewController
    elif isinstance(view, objc_util.ObjCInstance) and \
            (view.isKindOfClass_(UIView) or
                view.isKindOfClass_(UIViewController)):
        viewobj = view
    viewResponder = viewobj.nextResponder()
    try:
        while not viewResponder.isKindOfClass_(UIViewController):
            viewResponder = viewResponder.nextResponder()
    except AttributeError:
        return None
    return viewResponder



def presentAsSheet(view, sourceView=None, whenPresented=None):
    #### create a new modal view controller and set its presentation
    #### style to the sheet style, and size it to the content
    currentvc = getUIViewController(view)
    if currentvc is not None:
        currentvc.view = None
    sheetController = UIViewController.new().autorelease()
    sheetController.view = view.objc_instance
    sheetController.modalPresentationStyle = UIModalPresentationFormSheet
    sheetController.modalTransitionStyle = \
                                    UIModalTransitionStyleCoverVertical
    sheetController.preferredContentSize = \
                            objc_util.CGSize(view.width, view.height)

    #### retrieve the presentation controller for the new modal
    #### view controller, bail if that fails for some reason
    presentationController = \
        sheetController.presentationController()
    if presentationController is None:
        print("Unable to get presentation controller to present.")
        return

    #### find the view controller which is presenting the source view,
    #### that view controller will present the sheet overlay
    if sourceView is not None:
        sourcevc = getUIViewController(sourceView)
    else:
        sourcevc = getRootUIViewController()
    if sourcevc is None:
        print("Unable to find view controller for source view.")
        return

    #### create a block to call the presentation completion
    _block = None
    if whenPresented:
        _block = objc_util.ObjCBlock(
            whenPresented,
            restype=None,
            argtypes=[]
        )

    #### present the view controller containing the content view
    #### via the sheet presentation controller
    sourcevc.presentViewController_animated_completion_(
                                        sheetController, True, _block)



main = None

def whenPresented():
    print("PRESENTATION COMPLETE")

def presentSheet(sender):
    print("PRESENT SHEET:", sender)
    sheet = ui.View()
    sheet.frame = (0,0,300,200)
    sheet.background_color = (1.0,1.0,1.0,1.0)

    l = ui.Label()
    l.text = "Sheet Presented View"
    l.text_color = (0,0,0,1.0)
    l.alignment = ui.ALIGN_CENTER
    l.frame = (0,0,300,200)
    sheet.add_subview(l)

    #### presenting with a completion function crashes!
    presentAsSheet(sheet, main, whenPresented=whenPresented)

    #### presenting without completion function works fine...
    #presentAsSheet(sheet, main, whenPresented=None)



main = ui.View()
main.background_color = (1.0,1.0,1.0,1.0)
main.frame = (0,0,500,500)

b = ui.Button()
b.frame = (10,10,200,40)
b.title = "Present Sheet"
b.action = presentSheet

main.add_subview(b)
main.present("fullscreen")

I can't get the block to run without a segmentation fault.
presentViewController_animated_completion_(...) is defined here:
https://developer.apple.com/documentation/uikit/uiviewcontroller/1621380-presentviewcontroller

And it says it has no return and takes no parameters...so I'm not sure where I've gone wrong. Has anyone been successfully using blocks in python3/pythonista3.4?

[cvp]

@shinyformica you're right, even this small script using block crashes with segmentation error

# coding: utf-8
from objc_util import ObjCInstance, ObjCClass, ObjCBlock, c_void_p

def handler(_cmd, _data, _error):
    print(ObjCInstance(_data))

handler_block = ObjCBlock(handler, restype=None, argtypes=[c_void_p, c_void_p, c_void_p])

def main():
    CMAltimeter = ObjCClass('CMAltimeter')
    NSOperationQueue = ObjCClass('NSOperationQueue')
    if not CMAltimeter.isRelativeAltitudeAvailable():
        print('This device has no barometer.')
        return
    altimeter = CMAltimeter.new()
    main_q = NSOperationQueue.mainQueue()
    altimeter.startRelativeAltitudeUpdatesToQueue_withHandler_(main_q, handler_block)
    print('Started altitude updates.')
    try:
        while True:
            pass
    finally:
        altimeter.stopRelativeAltitudeUpdates()
        print('Updates stopped.')

if __name__ == '__main__':
    main()

[cvp]

@shinyformica I have another script where an ObjcBlock works correctly. This, the problem should occur with presentViewController_animated_completion_ with a block, I guess

[shinyformica]

@cvp so...you do have an example where ObjCBlock works without a crash? I definitely would want to look at an example that still works and try to discern what has changed.

[cvp]

@shinyformica Oups, sorry. I thought I had a working example but... The program works until I tap a button where action uses block. I did not check correctly. I apologize.

[shinyformica]

@cvp well darn, seems like ObjCBlock is genuinely broken, then? That's...not ideal. We use blocks in a quite a few places where our code has to interact with the objective-c side of things. So this situation basically bricks our code with pythonista3.4.

I wonder what has changed? Anyone out there (maybe @JonB or even @omz) have any thoughts?

[cvp]

@shinyformica Don't forget that Pythonista doc says "Warning
Block support is experimental. If you have the alternative of using an API that doesn’t require blocks, it is strongly recommended that you do so."

[JonB]

@shinyformica I wonder if you need to hang onto the reference to _block? I know some things have changed timing wise, the function might be exiting faster than that objc callback uses the block.

I wonder if it would make sense to switch over to rubicon -- IIRC there are some features that make using objc much less error prone.

Does the simple example in the docs for ObjCBlock still work?

(Never mind... @cvp example uses a global and still a problem)

I can try playing around with it a bit. IIRC, back when objc was first introduced in pythonista2, we had to do a lot of manual block structure definition and CFUNCTYPE stuff to define blocks. Might go back and look at those early threads to go back to basics sort of speak.

[shinyformica]

@JonB funny you should mention Rubicon, I'm just investigating that route now. I should try the simple example in the docs.

@cvp ...yes, I know it says it's "experimental" in the docs, but it did work fine before. If there was a change that broke it, it would be a shame to lose functionality.

[cvp]

@shinyformica this script with ObjcBlock works

from objc_util import *
from time import sleep
def Country_reverseGeocodeLocation(lat,lon):
	global handler_done,ISOcountryCode
	handler_done = None
	ISOcountryCode = None
	def handler(_cmd,obj1_ptr,_error):
		global handler_done,ISOcountryCode
		print('handler called')
		try:		
			if not _error and obj1_ptr:
				obj1 = ObjCInstance(obj1_ptr)
				for CLPlacemark in obj1:
					ISOcountryCode = str(CLPlacemark.ISOcountryCode())
					if ISOcountryCode == 'None':
						# special case of Market Reef island which belongs to Sweden and Finland,
						# and Apple reverseGeocodeLocation does not return an ISOcountryCode
						# check if location name = Bottenhavet (see of island), simulate
						# returns Finland. Market Reef entity will be identified later
						#print(str(CLPlacemark.name()))
						if str(CLPlacemark.name()) == 'Bottenhavet':
							ISOcountryCode = 'FI'
		except Exception as e:
			print('error',e)
		handler_done = True
		return
		
	CLGeocoder = ObjCClass('CLGeocoder').alloc().init()
	handler_block = ObjCBlock(handler, restype=None, argtypes=[c_void_p, c_void_p, c_void_p])	
	CLLocation = ObjCClass('CLLocation').alloc().initWithLatitude_longitude_(lat,lon)
	CLGeocoder.reverseGeocodeLocation_completionHandler_(CLLocation, handler_block)	
	# wait handler called and finished
	while not handler_done:
		sleep(0.01)
	return ISOcountryCode
	
lat,lon = (-51.6500051, -58.4924793)
print(Country_reverseGeocodeLocation(lat,lon))

[shinyformica]

@cvp oh! Fantastic, thanks for finding that. Interesting...have to try and see why that formulation is working. Good to have a working example.

[cvp]

@shinyformica I have to say that I have tested ten scripts I had before I find this one...

[shinyformica]

@cvp possibly just luck that this particular script works. But maybe there's something about the way it is set up. I had not found a working example so far in any of the ways we had been using ObjCBlock, and I'd also tried a couple of examples in the forum, like that barometer one.

[cvp]

@shinyformica Perhaps this use of wait/sleep

[cvp]

@shinyformica your, modified, script does not crash but hangs, like if the handler was never called

import objc_util
import ui
from time import sleep

UIViewController = objc_util.ObjCClass("UIViewController")
UIView = objc_util.ObjCClass("UIView")
UIModalPresentationFormSheet = 2
UIModalTransitionStyleCoverVertical = 0

def getRootUIViewController():
    app = objc_util.UIApplication.sharedApplication()
    window = app.delegate().window()
    if not window: return None
    return window.rootViewController()

def getUIViewController(view):
    #### If the view is a standard pythonista ui.View, we can
    #### try to directly retrieve the view controller
    SUIView = objc_util.ObjCClass('SUIView')
    SUIViewController = objc_util.ObjCClass('SUIViewController')
    UIView = objc_util.ObjCClass('UIView')
    UIViewController = objc_util.ObjCClass('UIViewController')

    if isinstance(view, ui.View):
        viewobj = view.objc_instance
        vc = SUIViewController.viewControllerForView_(viewobj)
        if vc is not None: return vc
    elif isinstance(view, objc_util.ObjCInstance) and \
            view.isKindOfClass_(SUIView):
        viewobj = view
        vc = SUIViewController.viewControllerForView_(viewobj)
        if vc is not None: return vc
    #### Otherwise we have to search the "responder chain"
    #### for the first instance of a UIViewController
    elif isinstance(view, objc_util.ObjCInstance) and \
            (view.isKindOfClass_(UIView) or
                view.isKindOfClass_(UIViewController)):
        viewobj = view
    viewResponder = viewobj.nextResponder()
    try:
        while not viewResponder.isKindOfClass_(UIViewController):
            viewResponder = viewResponder.nextResponder()
    except AttributeError:
        return None
    return viewResponder



def presentAsSheet(view, sourceView=None, whenPresented=None):
    #### create a new modal view controller and set its presentation
    #### style to the sheet style, and size it to the content
    currentvc = getUIViewController(view)
    if currentvc is not None:
        currentvc.view = None
    sheetController = UIViewController.new().autorelease()
    sheetController.view = view.objc_instance
    sheetController.modalPresentationStyle = UIModalPresentationFormSheet
    sheetController.modalTransitionStyle = \
                                    UIModalTransitionStyleCoverVertical
    sheetController.preferredContentSize = \
                            objc_util.CGSize(view.width, view.height)

    #### retrieve the presentation controller for the new modal
    #### view controller, bail if that fails for some reason
    presentationController = \
        sheetController.presentationController()
    if presentationController is None:
        print("Unable to get presentation controller to present.")
        return

    #### find the view controller which is presenting the source view,
    #### that view controller will present the sheet overlay
    if sourceView is not None:
        sourcevc = getUIViewController(sourceView)
    else:
        sourcevc = getRootUIViewController()
    if sourcevc is None:
        print("Unable to find view controller for source view.")
        return

    #### create a block to call the presentation completion
    _block = None
    if whenPresented:

        _block = objc_util.ObjCBlock(
            whenPresented,
            restype=None,
            argtypes=[]
        )

    #### present the view controller containing the content view
    #### via the sheet presentation controller
    sourcevc.presentViewController_animated_completion_(sheetController, True, _block)
                   

main = None

def whenPresented():
    global handler_done
    print("PRESENTATION COMPLETE")
    handler_done = True

def presentSheet(sender):
    global handler_done
    handler_done = None
    print("PRESENT SHEET:", sender)
    sheet = ui.View()
    sheet.frame = (0,0,300,200)
    sheet.background_color = (1.0,1.0,1.0,1.0)

    l = ui.Label()
    l.text = "Sheet Presented View"
    l.text_color = (0,0,0,1.0)
    l.alignment = ui.ALIGN_CENTER
    l.frame = (0,0,300,200)
    sheet.add_subview(l)

    #### presenting with a completion function crashes!
    presentAsSheet(sheet, main, whenPresented=whenPresented)
    # wait handler called and finished
    while not handler_done:
      sleep(0.01)

    #### presenting without completion function works fine...
    #presentAsSheet(sheet, main, whenPresented=None)



main = ui.View()
main.background_color = (1.0,1.0,1.0,1.0)
main.frame = (0,0,500,500)

b = ui.Button()
b.frame = (10,10,200,40)
b.title = "Present Sheet"
b.action = presentSheet

main.add_subview(b)
main.present("fullscreen")

[shinyformica]

@cvp doesn't seem to be the time.sleep() that allows the reverse geocode example to work...if I strip that code down a bit, and remove the sleep, it still works without crashing:

import objc_util
import time

handler_done = None
country_code = None

def handler(_cmd, placemarks, error):
    global country_code
    global handler_done

    print('handler called')
    if not error and placemarks:
        placemarks = objc_util.ObjCInstance(placemarks)
        for placemark in placemarks:
            country_code = str(placemark.ISOcountryCode())

    handler_done = True

handler_block = objc_util.ObjCBlock(
    handler,
    restype=None,
    argtypes=[objc_util.c_void_p, objc_util.c_void_p, objc_util.c_void_p]
)

lat, lon = (37.7749, -122.4194)
CLGeocoder = objc_util.ObjCClass('CLGeocoder').alloc().init()
CLLocation = objc_util.ObjCClass('CLLocation').alloc().initWithLatitude_longitude_(lat,lon)
CLGeocoder.reverseGeocodeLocation_completionHandler_(CLLocation, handler_block)	

# wait handler called and finished
while not handler_done:
    #time.sleep(0)
    pass

print("Country Code:", country_code)

So, something else about that particular block call works.

[shinyformica]

And if I make the barometer example nearly identical in structure, it still fails, even with a time.sleep() put in:

import objc_util
import time

pressure = None

def handler(_cmd, data, error):
    global pressure
    print("handler called")
    pressure = objc_util.ObjCInstance(data).pressure()

handler_block = objc_util.ObjCBlock(
    handler,
    restype=None,
    argtypes=[objc_util.c_void_p, objc_util.c_void_p, objc_util.c_void_p]
)

CMAltimeter = objc_util.ObjCClass('CMAltimeter')
NSOperationQueue = objc_util.ObjCClass('NSOperationQueue')

if not CMAltimeter.isRelativeAltitudeAvailable():
    print('This device has no barometer.')
else:
    altimeter = CMAltimeter.new()
    mainq = NSOperationQueue.mainQueue()
    altimeter.startRelativeAltitudeUpdatesToQueue_withHandler_(mainq,
                                                               handler_block)

    try:
        while pressure is None:
            time.sleep(0)
    finally:
        altimeter.stopRelativeAltitudeUpdates()

    print("got pressure:", pressure)

so something else is going on here.
Must be something more fundamental in how the blocks are defined.

[shinyformica]

One more datapoint. As @JonB suggested, I tried the example for ObjCBlock in the pythonista docs for the objc_util module:

import objc_util

cheeses = objc_util.ns(['Camembert', 'Feta', 'Gorgonzola'])

print(cheeses)

def compare(_cmd, a, b):
    a = objc_util.ObjCInstance(a).length()
    b = objc_util.ObjCInstance(b).length()
    if a > b: return 1
    if a < b: return -1
    return 0

# Note: The first (hidden) argument `_cmd` is the block itself, so there are three arguments instead of two.
compare_block = objc_util.ObjCBlock(
    compare,
    restype=objc_util.NSInteger,
    argtypes=[objc_util.c_void_p, objc_util.c_void_p, objc_util.c_void_p])

sorted_cheeses = cheeses.sortedArrayUsingComparator_(compare_block)
print(sorted_cheeses)

works fine, no crashes. So, that makes it seem even more likely that this has to do with the internals of how the block is created/presented to objective-c via CFFI.

[shinyformica]

Looks like rubicon may be the answer. Here's the same barometer example that crashes using objc_util converted to use rubicon:

import sys
import rubicon_objc
import time

pressure = None

def handler(data, error):
    global pressure
    data = rubicon_objc.api.ObjCInstance(data)
    error = rubicon_objc.api.ObjCInstance(error)
    print("handler called:", data, error)
    pressure = data.pressure.floatValue

handler_block = rubicon_objc.api.Block(
    handler,
    None,
    rubicon_objc.types.c_void_p,
    rubicon_objc.types.c_void_p
)

CMAltimeter = rubicon_objc.api.ObjCClass('CMAltimeter')
NSOperationQueue = rubicon_objc.api.ObjCClass('NSOperationQueue')

if not CMAltimeter.isRelativeAltitudeAvailable():
    print('This device has no barometer.')
else:
    altimeter = CMAltimeter.new()
    mainq = NSOperationQueue.mainQueue
    print("Altimeter:", altimeter)
    print("Main Queue:", mainq)

    altimeter.startRelativeAltitudeUpdatesToQueue_withHandler_(mainq,
                                                                handler_block)

    try:
        while pressure is None:
            pass
    finally:
        altimeter.stopRelativeAltitudeUpdates()

    print("got pressure:", pressure)

this doesn't crash. I don't know rubicon particularly well, so I don't know if I'm using it exactly as intended, but I'll see if it succeeds in other cases where objc_util crashes.

[cvp]

@shinyformica said

doesn't seem to be the time.sleep() that allows the reverse geocode example to work...if I strip that code down a bit, and remove the sleep, it still works without crashing:

I'm sure that some years ago, I have had to add this wait loop to get this code working. But ok, it is included in a very big script and was running in a separate thread.