The term iCloud regroups several technologies. As far as I know the simplest one a basic key-value store works very well, I use it without any problems. However, last year I tried to integrate CoreData syncing through iCloud in one of my apps and I couldn't make it work reliabily, I spent a lot of times I tried many things, but usually there always was some irrecoverable corruptions that ended-up preventing any syncing. I never shipped this code, I was too afraid, it was too brittle. I haven't retried since. I heard the situation has improved but I don't know for sure, it was such a nightmare that I simply avoid to spend any more time on this api.
iCloud in general "just works". It was pretty terrible from the get-go, from reliability to really egregious bugs in the OS, but at this point is pretty stable.
The real problem here is the combination of iCloud and Core Data (for non-Apple folks, the built-in persistence/object model framework).
In a somewhat simplified way, Core Data is a data store most commonly backed by SQLite. It's used everywhere from your mail app to the Facebook app. It's handy and convenient when it isn't trying to kill you - it's one of the more complex frameworks that Apple ships, and the documentation is extremely poor for it. It also doesn't help that there is a lot of quirky behavior that's more or less tribal knowledge to long-time Apple devs and WWDC attendees, and is has enough concurrency gotchas to fill a container ship.
So, Core Data is not the simplest piece of code to work with from the get-go, and then you pile iCloud on top.
iCloud is conceptually pretty simple - there's a directory on your file system that is replicated to Apple's servers, and back down to each one of your devices. When files change the OS sends notifications to your app informing you of such. If you're using iCloud as a distributed file system (a la Dropbox), it's easy to integrate.
The trouble with this model is that Core Data stores can be in fact quite large. If you have a 30MB database of, say, recipes on your disk, you really don't want to resend the whole thing every time your user alters a row. Apple special-cases Core Data stores in iCloud by sending only deltas, but the implementation is utterly broken:
- There is no baseline state(s). The database is literally the playback of every delta, with no canonical snapshots. Ever.
- iCloud is really bad at sequencing the deltas, especially if (somewhat) concurrent changes are happening. Core Data is also terrifyingly bad at conflict resolution when deltas from different devices don't line up.
- The above points means that it's trivially easy to break your entire database, as your deltas no longer play back to a sane database file. When this occurs there is no way to roll back your database, since there is no concept of a snapshot or last known good state.
- This is compounded by some really horrible API design on Apple's part. When your iCloud database becomes corrupt it fails silently, with absolutely no API that allows one to determine said broken state. Your app literally stops working with none of the OS making a single peep, and no way for you to proactively check your database's state. iCloud seems to print some debug things into your console indicating this failure, but neither your app nor your users have access to it. This manifests in your app (and in tech support requests) as "iCloud just stopped syncing" - your device stops transmitting deltas and simply works off of the last locally-cached good state, all without telling the dev or the user.
- This is further compounded by the fact that the entirety of Core Data+iCloud was rushed out the door. Documentation was non-existent even up to the day the new version of iOS went out to the public. There was literally only one source of information: a thread on the Apple dev forums that Apple engineers would sometimes pop into.
- This is further compounded by the fact that even the Apple engineers themselves seemed to have no idea how to implement an app with iCloud + Core Data. The example code (provided deep, deep within aforementioned thread) made 90 degree turns seemingly every few days. The same sample would have dramatically changing implementations from week to week. The Apple engineers in the thread seemed as mystified as the people trying to use the framework.
- The poor documentation and poor state of sample code, as well as what is IMO a fundamentally broken architecture means that iCloud + Core Data remains a complete nightmare to this day. I think the poor architecture is really the core of this here - while Apple could have provided better docs and better support, I believe the fundamental architecture choices made here means Core Data + iCloud would never have been workable.
- The icing on top of the cake was an extremely egregious bug that existed at launch (unsure now, you couldn't pay me enough money to work with that API ever again). "Okay, so our deltas are completely fucked" you say, "Why don't we just delete the app's entire iCloud bucket and start over?"
A jolly good idea until you realize that a bug in iOS/iCloud means that when you delete an app's iCloud storage "bin", it cannot be recreated by that app, ever again.
A lot of the more recent iOS core apps and APIs seem either poorly conceived or implemented, or both. Auto Layout is a train wreck. Storyboards seem like a nice idea until you really start using them, Core Data + iCloud horror stories abound. Maps was a fiasco etc.
Cocoa Touch + Obj-C is a very nice platform in a lot of ways but I'm losing faith in Apple's software architects. Contrast this with Android and even though I think Java is a poor choice for mobile development their engineering teams really seem to know what they're doing.
Java was a great choice for the technical goals the Android engineering team was trying to achieve (cross-architecture portability, easier transition for non-mobile developers, etc.). The problem was that those technical goals turned out to be not very helpful in terms of meeting Android's strategic goals, given the way the mobile OS/device market has evolved.
That's a mistake at a level above engineers and software architects (or at least a mistake so far - if, hypothetically, Intel managed to crack their mobile CPU problem the choice of Java would turn out to be very smart). This is the dual of Apple's situation with iCloud. The strategic choice to start building out cloud services to support their ecosystem is clearly the right one, it is the implementation that has missed the mark (so far).
I understand the short-term reasoning for choosing Java. Unfortunately mobile is one platform where transparent access to native code is a huge advantage and Java/JNI puts Android at a huge disadvantage here compared to Obj-C/C++.
This is why writing something like a Twitter client is actually much easier in Android but doing something really interesting like realtime multimedia or highly responsive, complex UIs is difficult to the point of impossible in some cases.
Auto Layout has been a godsend for me. What trouble are you having with it? In particular, I use the 10.8 NSSplitView support to manage resizing behavior without any code.
For simple things it's fine but it's a real nuisance to work with in IB or in code and complex layouts get out of hand very quickly. The shorthand layout language is cryptic enough to impress a Perl programmer.
I think Android and WP's XML-based structural layouts are far, far easier to work with, understand, modularize, and reuse.
I don't know much about Android's layout, but from what I have seen, it looks rather ad-hoc. For example, LinearLayout (http://developer.android.com/reference/android/widget/Linear...) looks to be a core layout class. It has boolean properties like "baselineAligned" and "measureWithLargestChild;" these appear to have been added as needs arose, instead of being part of a general layout theory.
Autolayout, on the other hand, has a more general approach of establishing relationships between properties of views. Baseline alignment then just falls out: make view1.baseline = view2.baseline, or view1.top = view2.top for top alignment if you prefer. Equal widths fall out too: view1.width = view2.width. If you want a vertical stack you can write view1.bottom = view2.top. If you want a fixed aspect ratio (say, 4/3), you can write view1.width = view1.height * 4/3.
The result is that it's possible to directly express complex layout ideas. For example, "make three buttons baseline aligned, 10 pixels apart, all of them equal width, none of them clipping their labels. If they cannot fit, then in turn: shrink the padding down to 4 pixels, don't require them to be equal width, truncate the first button's label, or lastly then grow the window / make the view scrollable, until they fit."
That's an unrealistically elaborate example, but with autolayout it can be done entirely in IB, without any code at all. I am guessing with Android it would take a fair amount of manual work.
So my view from a distance is that the autolayout approach is more general and elegant, while the Android approach may handle simple cases easily, but is more ad-hoc and random.
You should try actually building some complex Android UIs. You might find it eye-opening after working with iOS for a long time. I certainly did.
It's true that AutoLayout's systems of interdependent linear equations are strictly more powerful than Android's structural layouts but they're a far more awkward solution to the vast majority of common UI layout problems. In practice Android UIs are far, far easier to write and maintain. Debugging the kind of complex AutoLayout schemes you describe can quickly become a nightmare. The structural approach taken by Android and WP is far more natural for the kinds of UIs you actually find in the field.
Also, Android's CSS-like style system makes it far easier to define app-wide constants like grid spacing, margins, button padding etc and to change them in one place.
I haven't developed for Android, but I do know that the interfaces for several major apps I saw were hilariously bad on large screens--literally just the small-screen phone interfaces floating in empty space.
Responsive design is one of Android's most fundamental design principles. It just took a while (and a few million tablet sales) for developers to take the platform seriously.
Most new android apps are responsive these days. And those companies that maintain their existing apps are busy adding big screen support.
The Skype screenshot is from last year. It was't the only one; another was the Netflix app, and Facebook was really bad: http://i.imgur.com/fSQYQex.png
I'm glad to hear that companies are busy adding big screen support, though that support is arguably coming late. The main point is that an Android app's interface could be stretched across anything, and this has certainly been a design obstacle in the past.
It's not an obstacle it's just laziness. Unlike the iPad you basically get a usable tablet UI for free with Android. Android's fragment API makes it a lot easier than he iPad to adapt to a proper tablet UI if you want.
> Unlike the iPad you basically get a usable tablet UI for free with Android.
I just posted two screenshots showing otherwise.
> Android's fragment API makes it a lot easier than he iPad to adapt to a proper tablet UI if you want.
And this is just ridiculous. Regardless of whether you prefer iPads or Androids, iPads are most decidedly easier to design tablet UIs for because there are so few screen sizes.
wow. thanks for writing that up. if it's any consolation, you likely just saved me untold amounts of pain as i am wrangling with what approach to take for saving a small but not trivial amount of structured data in my app. this pretty much rules out core data!
Don't rule out Core Data! It's very nice (especially with the new concurrency APIs); it hasn't yet been brought totally up to speed with iCloud, but it's been improving every year. Remember that OS X is on annual releases now, so there will be more improvements this year and so on.
I wouldn't rule out core data just from this post. Core data may have some quirks, but it's pretty reliable and very useful from my experience. I haven't given iCloud + core data a try, since I wasn't sure if it were reliable yet.
I've not used the APIs in question, but I'm not sure how this can be totally unexpected, given the marketing promises and the actual technical goals. I read your comment as: "Transparent distributed storage? What could possibly go wrong!"
Given how much work they spent trying to reinvent iCloud you would think they would have made it more seamless for developers. Apple really needs to take some of the open source CoreData wrappers (which make life so much easier) and add them to the framework.
The biggest joke is that WebObjects EOF on which CoreData is based used to be really simple. Not sure what happened.
As if Apple reads those. Apple doesn't care about developers, they only care about their real customers; people that don't know how a computer works. I know this because I am a developer and Xcode still uses all the memory and creates a zombie process everytime I run on the simulator.
It's clear that Apple engineers do read those bug reports. Any amount of time spent interacting with them publicly will have them directing people to the bug reporter quite often. Their development process appears to be very data-driven; even redundant bug reports that get closed as duplicates are factored into determining bug priority.
That site enters directly into Radar the internal bug tracking system where ALL bugs are triaged. It is very much used.
And I my suggestion for your issue (which I have seen in the past but definitely isn't consistent) is to try restarting Xcode and getting rid of preferences.
I was just about to try and convert my app to use iCloud, and incorporate the features in a 2nd one. After going to the 2011 conference, I followed the message and took the extra effort to put the 1st app's information in Core Data, and then only afterwards heard how bad iCloud was. Now I'm thinking of moving my data back to a document-based architecture. Now there's grousing that even that sucks.
If iCloud was hitting on all cylinders, then Apple could kill MS Surface by having seamless sync between laptops and tablets. Instead of a chunky tablet/laptop that's mediocre at being both, you can have a fabulous tablet and a great ultra-lightweight laptop and not have to worry about syncing. Need to pass around something to show a coworker? It could just work.
This is a sign that Apple is either not hitting on all cylinders, or bit off more than it could chew. (To be fair, distributed data is, and always has been, quite a hard problem.) Apple could be moving in for the kill. Instead, they're recovering from stumbles while their opponent has left themselves wide open.
Syncing does generally just work between laptop and tablet.
I add a Safari bookmark on one and it appears instantly on the other. Likewise for contacts, calendars, apps, music and any iCloud enabled app e.g. Coda.
Then just add Dropbox and Evernote and you're laughing.
Yeah, I have no issues with Core Data. It's also not so complex, IMO. I'm going to have to do a migration to iCloud document for existing users with my next release, though.
To all those suffering from Core Data + iCloud syncing: we built Simperium (YC S10) to solve this problem. The iOS/OSX and JavaScript libraries are open source, with the backend to follow (or you can use the hosted service). The site is at http://simperium.com and the repos are at http://github.com/Simperium
We were recently acquired by Automattic, and we're now putting more resources into the project (for example to make it work on Android as well). If cost for the hosted service is a concern for you, you can get in touch and we'll work something out (info@simperium.com).
Instead of waiting two years, why not implement your own sync service? I know that sounds like snark, but using something like CouchDB and TouchDB can give your users an experience similar to the one promised by iCloud.
I'm very interested in those two solutions. Does anyone here have some experience about CouchDB/TouchDB on iOS/Android? Specifically:
Does it replicate reliably to a CouchDB or Couchbase server?
How are conflicts handled?
Are there wrappers already available that map to ObjC/Java native data structures, similar to couchdbkit on python?
Hey yeah I've used TouchDB on iOS quite a bit. It syncs reliably to Couchdb - I actually haven't tried couchbase. Conflicts are handled in the default couchdb way I think - I haven't really touched on this much. TouchDB syncs to native structures that are derived from CouchModel.
Oh, one more thing: Did you ever load multiple TouchDBs? I'm thinking the overhead per DB (not per server) should be pretty small, no?
Background: I'd like to build an application where I separate entities into multiple couchDBs, partly since it saves me view definition code, partly because it gives me more flexibility for per-document access permissions.
Yes I have a framework that splits itself into 3 databases and has quite a lot of attachments. There isn't a big overhead as far as I can see. Does couchDB do what you need with per-document access permissions? It seems to be the biggest downside to couchdb is having to do so many workarounds for per-document access permissions.
That's also my conclusion. However I'm not aware of a DBMS that
- is document based
- can easily replicate to laptops and embedded devices
- has all the security I want, e.g. encryption, per document security
- has the bindings I want and/or a new binding can easily be implemented ad-hoc
Given the advantages and disadvantages I'm leaning towards CouchDB and rolling my own security wrapper. IMO that's still better than going with an RDBMS and then implementing replication[1]. How do you see this?
[1]edit: and also giving up the document based approach, thus not having arbitrary mapping from the get go.
I love couchdb for its replication, not only did I use it for a previous company I worked for and still contract with, I'm using it for my 'big idea' project. Once you have data replication you do need some kind of different approach to user/document security - after all they can take the data they have and do anything with it - so you need to treat replication as data input and validate there, like couchDB does.
I think the real downsides are scaling and performance but there are options at least. Given that TouchDB is essentially couchdb mapped onto sqlite I do wonder if there are going to be good options to map couchdb replication onto postgres in future.
[edit: sorry, I replied here, because it wouldn't let me reply to your other answer first and I thought it was because we've reached some kind of maximum depth]
Thanks, I see. Ok, if it's just string or binary based it will work from a correctness standpoint. I'd expect big performance problems with ad-hoc views (if they even exist here), but these shouldn't be used in production anyways. Also, I'd expect replication to take quite a bit longer because it needs to map every document with changes, so there's going to be a tradeoff between initialization time and replication time between the two approaches.
I'm thinking it's going to be beneficial for larger databases to have a TouchDB 'server' somewhere, which constantly replicates with CouchDB and sends the devices a complete snapshot sqlite file for the initial setup. After that, they can talk to CouchDB directly. Otherwise it could take like half an hour to initialize a 50MB DB on a device, which is not really feasible.
In fact for a while you could only have adhoc views, but my knowledge is 6 months out of date.
Yes definitely do that. I bundle the sqlite in the app store updates and then mount that as an external db and pull from itself - its a bit awkward but it worked. I had to write the external db stuff, but it was pretty easy.
oh, so TouchDB maps to sqlite? Does that work generally? Let's say my documents have lists of maps of tuples of lists - will it create the appropriate table structure in sqlite?
The use cases I have in mind don't need the DB to scale to more than a few ten thousand users. Should be ok with a two or three replicated nodes I think, from my experience with Lotus Notes.
I think each document is a row and it parses it to native structures on load. I think I saw something on the dev list about that being improved - but its something to check if it matters.
Yeah with my apps I haven't noticed many iCloud related problems. I generally however just store simple keys in iCloud then pull the real data from my server based on those. It's not as robust as I'd like it but works.
I write my own backends. I feel safer that way. Already got a framework for communicating with a resource based API properly with its local model (Always Core Data unless not trivial like a map).
I've never worked with iCloud, so I'm curious: why do devs say that Dropbox is so much better than iCloud? From what I've seen, both work similarly in that they abstract out the cloud as part of the file system. Wouldn't you still have to resolve conflicts and do all that other dirty stuff if you use Dropbox?
Edit: potatolicious has a pretty great explanation. It looks like it's mostly CoreData issues. But for those cases, Dropbox wouldn't do any better, right?
I've heard these rumblings for quite a while--haven't done anything with iCloud support myself--, and, yes, we need some details of what's not working.
Or maybe the article's implying no one really knows?
All of your submissions for the last week have been autokilled. Something must have triggered a spam detector. Or maybe the Youtube submission (brilliant video) did it. Your comments are still visible, though. Writing polite email to PG is probably your best recourse.
I won't argue that CoreData has its pitfalls, but at the end of the day, many of us both write our own syncing solutions, and successfully use iCloud. Neither of these things is actually all that hard, and you certainly don't need to use iCloud to have your apps featured.
Edit: I found this quite recent post with similar issues http://www.jumsoft.com/2013/01/response-to-sync-issues/