That Syncing Feeling

I’ve been interested in Mac/iOS app communication for some time now. While there are other options, most recently I’ve been exploring iCloud document syncing.

Apple has comparatively verbose documentation for iCloud (I prefer downloading the PDF), and Ray Wenderlich has not one but two tutorials, an introductory one (parts 1 and 2) and a more in-depth one (parts 1, 2, 3, and 4).

So while I’m going to talk about it at some length (and several blog posts), I don’t need to duplicate all that.

Instead, I’m going to fill in the gaps I found, and describe my own experiences.

I’ll mostly be talking about a sample app I wrote, called Documentary, that lets you make simple unformatted text documents and share them through iCloud, either to another device of the same type, or between Mac and iOS.

Part 1: Feeling Entitled

To run the iOS app on an iOS device, or the Mac app on your Mac, you’ll need to be able to support iCloud entitlements in your apps. To do that, you’ll need a paid $99/year iOS ADC account or a $99/year Mac ADC account, respectively

But what’s interesting is that, as far as I know, once you have your account(s) set up, you can download my sample code and run it, and with no other effort or changes on your part, the iCloud syncing portion of it will work right away.

Go ahead, build the iOS version (for example), and run it on two different devices, say your iPhone and an iPod touch. You can create a document on one, and it will show up a few seconds later (if you’re lucky) on the other.

For one, hey, that’s cool! Apple allows you to use its server storage even when you’re just playing around with an app. It doesn’t have to be an app you’ve registered to ship.

For two, notice that you’re using the same bundle identifier that, say, I am when I run my app, and yet there’s no worries about conflicting IDs on the iCloud servers.

This may seem strange to old Mac developers. But in the brave no-longer-so-new world of provisioning, the app ID is prefixed with your team ID (which Xcode 5 seems curiously reticent to ever show you, except in obscure error messages). Xcode handles the prefixing part of it without needing to include it in your project, and so you can use the same project that I use, while still getting your own app ID unique to you.

For three, if you build and run iOS, then Mac (or vice versa), you may get a complaint from Xcode about needing to add the iCloud entitlement again each time you build.

I’m not quite sure what’s going on under the hood, but I believe it might be because there’s no dedicated provisioning profile for each app yet. Remember that you didn’t register the app’s ID with Apple’s Dev Center website? That was a plus when you were just playing around. But it might come bite you here, if there’s some sort of temporary, fit-all-sizes profile that’s being used for both apps, and that keeps getting changed each time you build.

I was able to make the build error go away by registering those app IDs in, respectively, the iOS and Mac Dev Centers. That gives each of them an individual provisioning profile.

What’s curious is that even after I deleted the app entries again (and thus their profiles) and updated Xcode (and quit and restarted Xcode, for good measure), the builds continued to work repeatedly with no errors. So I’m not sure what’s going on under the hood. Makes it more likely it’s just a straight-up bug, eh? But keep an eye out for these problems if you try this for yourself.

Next up: What Apple’s documentation does and doesn’t say.