4 ms·

Facebook open-sources KVOController – simpler key-value observing for iOS

31 points by kimon 13y ago

vjeux 13y ago
At a first glance, this seems like Angular's digest loop. Can someone make a more elaborate comparison for people that know nothing about iOS?
- seivan 13y ago
  It's basically observing properties on NSObject subclassed classes. It doesn't work properly with UIKit, but most other stuff it works 'fine'. According to some smarter people than myself, the internals of KVO is a giant mess. But that's beyond me.
seivan 13y ago
Shameless plug. Here's mine https://github.com/seivan/SHKeyValueObserverBlocks#adding-observer-on-an-nsarray-to-keep-track-of-your-data-source https://github.com/seivan/SHKeyValueObserverBlocks#adding-ob... Comes with bi- and uni-bindings. I like mine better but I wouldn't have done the auto-removal of observers without Yan Raboviks swizzling magic https://github.com/rabovik/RSSwizzle https://github.com/rabovik/RSSwizzle credits due. I set a toggle in case you feel that's too dangerous to shut it off - Something I use. I compared a couple of ways of dealing with that, including writing some of my own and I think Yan does it the best. When doing my own I had some discussions with James Montgomerie regarding race conditions and dealing with class hierarchies. He had solved with a different way here himself: https://github.com/th-in-gs/THObserversAndBinders https://github.com/th-in-gs/THObserversAndBinders Here's the discussions between us regarding the swizzling magic (that Facebook also does here) https://github.com/th-in-gs/THObserversAndBinders/commit/a4cff51e0e465427594328be91026bd223718622 https://github.com/th-in-gs/THObserversAndBinders/commit/a4c... The pull requests leading up to me going with Raboviks library (due to better code and smarter implementation) Test for infinite loop when deallocating: https://github.com/seivan/SHKeyValueObserverBlocks/pull/5 https://github.com/seivan/SHKeyValueObserverBlocks/pull/5 New test to ensure dealloc of observed objects runs: https://github.com/seivan/SHKeyValueObserverBlocks/pull/2 https://github.com/seivan/SHKeyValueObserverBlocks/pull/2
- kimon 13y ago
  This is a useful collection of links. One point of note, Facebook's solution doesn't rely on swizzling. Much like THObserversAndBinders, KVOController ties observation to the controller scope. We use a shared controller instance, that acts as a receptionist for all KVO notifications, as well as a weak reference to the observer, in order to safely allow observer removal on dealloc.
  - seivan 13y ago
    Ah, thanks for correcting me. I didn't have time to go through it yet. https://github.com/facebook/KVOController#usage https://github.com/facebook/KVOController#usage By controller does the readme refer to the KVOController instance? I assume this is a property on the class that uses it, and once the class gets dealloced, its observer also get dealloced? FBKVOController Hmm... I think this is a much better idea! Much cleaner than what I current got going, but then again we don't offer the same api. Thanks for correcting me!
    - kimon 13y ago
      Correct. Add a strong reference from observer to KVOController instance via a property or instance variable and you've achieved un-observation on observer dealloc :) This usage pattern is quite common. We'll look into calling this out more explicitly in the readme. Thanks for the feedback!
natasham25 13y ago
KVO is built-in to iOS, but it has some serious issues. One BIG issue is that you have to register to observe a key in order to de-register from it later. If you never register for the key (because it is dynamic for example), and try to de-register, the app will crash. It's a pretty big issue, and this seems to handle it in a pretty elegant way.
- seivan 13y ago
  Elegant and elegant, the swizzle (alter it in runtime) the class to remove observers on dealloc (afaik I haven't seen the source yet)
- kimon 13y ago
  This was the principal motivation behind KVOController. Manually tracking registered observers is tedious and error prone. We hope you give KVOController a try, feedback from the community is welcome.
- morkfromork 13y ago
  I remove observers within a @try {} @catch{} block. The exceptions are caught and I can fix where necessary.
Greenisus 13y ago
I'm looking forward to trying this. KVO is very powerful (I used it extensively in my last app: Well), but it's delicate. Registering/unregistering, making sure you write methods to properly fire KVO events for collections, etc.
icodestuff 13y ago
Looks like it's implemented similarly to MAKVONotificationCenter, except that it doesn't support observation on arrays/array indexes. And why does it need to manually call the shared controller's -observeVFK... when the Initial option is set? That should be called automatically by the KVO machinery. It's a bit concerning. Also it seems like keeping track of the additional controller objects would be a PITA.
- kimon 13y ago
  KVOController 1.0.0 supports observing arrays and other ordered relationships, just not values within. I filed https://github.com/facebook/KVOController/issues/5 https://github.com/facebook/KVOController/issues/5 to track. Features requests are welcome. Performing the initial callback manually, avoiding the KVO initiated one, was shown to be a performance improvement under certain KVO configurations. We've updated the readme to include an example tracking the controller object. An instance variable should all that is necessary: https://github.com/facebook/KVOController https://github.com/facebook/KVOController.
  - icodestuff 13y ago
    > Performing the initial callback manually, avoiding the KVO initiated one, was shown to be a performance improvement under certain KVO configurations. Please elaborate. I've been re-implementing KVO, and have not seen this. What configurations? Also, adding a controller ivar/property is rather invasive, don't you think?

31 points by kimon 13y ago

vjeux 13y ago

At a first glance, this seems like Angular's digest loop. Can someone make a more elaborate comparison for people that know nothing about iOS?

seivan 13y ago
It's basically observing properties on NSObject subclassed classes. It doesn't work properly with UIKit, but most other stuff it works 'fine'. According to some smarter people than myself, the internals of KVO is a giant mess. But that's beyond me.

seivan 13y ago

Shameless plug. Here's mine https://github.com/seivan/SHKeyValueObserverBlocks#adding-observer-on-an-nsarray-to-keep-track-of-your-data-source https://github.com/seivan/SHKeyValueObserverBlocks#adding-ob... Comes with bi- and uni-bindings. I like mine better but I wouldn't have done the auto-removal of observers without Yan Raboviks swizzling magic https://github.com/rabovik/RSSwizzle https://github.com/rabovik/RSSwizzle credits due. I set a toggle in case you feel that's too dangerous to shut it off - Something I use. I compared a couple of ways of dealing with that, including writing some of my own and I think Yan does it the best. When doing my own I had some discussions with James Montgomerie regarding race conditions and dealing with class hierarchies. He had solved with a different way here himself: https://github.com/th-in-gs/THObserversAndBinders https://github.com/th-in-gs/THObserversAndBinders Here's the discussions between us regarding the swizzling magic (that Facebook also does here) https://github.com/th-in-gs/THObserversAndBinders/commit/a4cff51e0e465427594328be91026bd223718622 https://github.com/th-in-gs/THObserversAndBinders/commit/a4c... The pull requests leading up to me going with Raboviks library (due to better code and smarter implementation) Test for infinite loop when deallocating: https://github.com/seivan/SHKeyValueObserverBlocks/pull/5 https://github.com/seivan/SHKeyValueObserverBlocks/pull/5 New test to ensure dealloc of observed objects runs: https://github.com/seivan/SHKeyValueObserverBlocks/pull/2 https://github.com/seivan/SHKeyValueObserverBlocks/pull/2

kimon 13y ago
This is a useful collection of links. One point of note, Facebook's solution doesn't rely on swizzling. Much like THObserversAndBinders, KVOController ties observation to the controller scope. We use a shared controller instance, that acts as a receptionist for all KVO notifications, as well as a weak reference to the observer, in order to safely allow observer removal on dealloc.
- seivan 13y ago
  Ah, thanks for correcting me. I didn't have time to go through it yet. https://github.com/facebook/KVOController#usage https://github.com/facebook/KVOController#usage By controller does the readme refer to the KVOController instance? I assume this is a property on the class that uses it, and once the class gets dealloced, its observer also get dealloced? FBKVOController Hmm... I think this is a much better idea! Much cleaner than what I current got going, but then again we don't offer the same api. Thanks for correcting me!
  - kimon 13y ago
    Correct. Add a strong reference from observer to KVOController instance via a property or instance variable and you've achieved un-observation on observer dealloc :) This usage pattern is quite common. We'll look into calling this out more explicitly in the readme. Thanks for the feedback!

natasham25 13y ago

KVO is built-in to iOS, but it has some serious issues. One BIG issue is that you have to register to observe a key in order to de-register from it later. If you never register for the key (because it is dynamic for example), and try to de-register, the app will crash. It's a pretty big issue, and this seems to handle it in a pretty elegant way.

seivan 13y ago
Elegant and elegant, the swizzle (alter it in runtime) the class to remove observers on dealloc (afaik I haven't seen the source yet)
kimon 13y ago
This was the principal motivation behind KVOController. Manually tracking registered observers is tedious and error prone. We hope you give KVOController a try, feedback from the community is welcome.
morkfromork 13y ago
I remove observers within a @try {} @catch{} block. The exceptions are caught and I can fix where necessary.

Greenisus 13y ago

I'm looking forward to trying this. KVO is very powerful (I used it extensively in my last app: Well), but it's delicate. Registering/unregistering, making sure you write methods to properly fire KVO events for collections, etc.

icodestuff 13y ago

Looks like it's implemented similarly to MAKVONotificationCenter, except that it doesn't support observation on arrays/array indexes. And why does it need to manually call the shared controller's -observeVFK... when the Initial option is set? That should be called automatically by the KVO machinery. It's a bit concerning. Also it seems like keeping track of the additional controller objects would be a PITA.

kimon 13y ago
KVOController 1.0.0 supports observing arrays and other ordered relationships, just not values within. I filed https://github.com/facebook/KVOController/issues/5 https://github.com/facebook/KVOController/issues/5 to track. Features requests are welcome. Performing the initial callback manually, avoiding the KVO initiated one, was shown to be a performance improvement under certain KVO configurations. We've updated the readme to include an example tracking the controller object. An instance variable should all that is necessary: https://github.com/facebook/KVOController https://github.com/facebook/KVOController.
- icodestuff 13y ago
  > Performing the initial callback manually, avoiding the KVO initiated one, was shown to be a performance improvement under certain KVO configurations. Please elaborate. I've been re-implementing KVO, and have not seen this. What configurations? Also, adding a controller ivar/property is rather invasive, don't you think?