Double Vision in Xcode doesn’t Double Your Fun

The Mac developer scene is loaded with a lot of helpful and supportive developers out there, sharing ideas, code and encouragement with one another. I’ve benefitted from the development community, as have the Mori and Clockwork code. I say this not only as one who’s currently putting new code into them, but seeing the comments Jesse left in the code before me!

So I’d like to drop an idea into your lap you might find useful for the right type of application. As there are different types of software one can develop, e.g., operating systems, utilities, paint programs and the like, they have particular usage characteristics that they encourage. Some, like digital notebooks and desktop timers for example *cough*, tend to remain in operation while the user is logged into his account. Usually, this isn’t a problem for the user. Unless, of course, the user is also someone further developing said software. Then several questions have to be answered, such as, “How do I run unit tests on builds while still running a stable version of my app?” and “How do I try out the latest build without affecting the files which are currently open in my app?”

On operating systems based on more primitive process management, it isn’t troublesome because each built application is fairly independent of others, and often multiple invocations of a single app can be run concurrently. It wasn’t problematic on the Mac either back on MacOS 9 and earlier, and even in the early MOX releases. But now with Launch Services, running test versions of apps you run on an all-day basis can be problematic. It’s best to give that test version some different signature so its defaults and file changes don’t corrupt your normal environment.

Note that this tip doesn’t prevent two versions from munging the same files; even two unrelated apps can mess up a data file if they’re updating it at the same time. What this tip does is provide an alternate identity, if you will, for test builds so MOX doesn’t try to hand it the same data set it gives the release builds of your app. You mustn’t try to open files in the test build that are currently opened by a release build.

Here’s how I do it:

1. In the Info.plist file, use the C pre-processor’s conditional compilation directive to give your app its normal metadata when a release build is made, but a special set of metadata for all other build configurations:

#if defined(Release)

Update: I forgot to mention that Xcode 3 and later versions now use specialized editors for the Info.plist files. To override this editor selection, bring up the file’s Info window (by selecting the file and pressing cmd-I) or the Inspector window and change the File Typesetting from “text.plist.whatever” to “text”. Once you add the conditional to Info.plist you can change File Type back and access Info.plist in its raw form from its target’s Properties tab. That way, you can view it in either mode within Xcode. However, making any changes in Xcode’s plist editor will wipe out any conditional directive in the file, so use it only for reviewing current settings, not for actual editing!

2. In the Target Info window (brought up via the ‘Project > Edit Active Target “Mori”‘ menu item), select the Build tab, specify “All Configurations” for the Configuration pop-up menu, and enter “plist” in the search toolbar widget to bring up the relevant setting items.

3. For the “Info.plist Other Preprocessor Flags” setting, enter -traditional as the value. While not needed to support the test version twin, it will help to prevent any URLs included in the Info.plist from being swallowed up by the pre-processor and possibly causing you sleepless nights because neither MOX nor the Xcode build system have the slightest idea of what the proper format for URLs are, but will behave erratically when it isn’t just so. So it’s best to make it a non-issue from the start. (No charge for that and other tips related to usage of the pre-processor you can find in Technical Note TN2175. Incidentally, TN2175 says to use “-traditional”, but I use “-CC”. Use whatever works for the version you’re on.)

4. For the Info.plist Preprocessor Definitions setting, enter $(CONFIGURATION). Xcode will change the display to read <multiple values>, but that’s okay because the value will vary according to the current build configuration. It will define a value that matches the build configuration that the pre-processor will test against in the Info.plist. (Try switching the setting in the Configuration pop-up menu of the Build tab to watch the value change to match the current setting.) This is what will direct the pre-processor to output the correct value for CFBundleIdentifier.

5. Check the Preprocess Info.plist File checkbox so Xcode invokes the pre-processor on the Info.plist before copying it to the application.

When built, you’ll be able to run the app concurrently with the release version, and without causing conflicts with data files in use by it. Of course, you won’t have your preferences set up, but that’s only a problem until you save preferences for the test version. (Remember, if you try to get around that problem by copying the release version’s defaults file that it also holds the recently opened files. Purge, close or what-have-you as appropriate!)

One of the extra things I attempted to do in this technique was to provide an alternate name for the private builds or test versions so they would be distinctly named for testers. We used to use naming conventions such as “Mori 1.7β4″ when distributing such versions back in the pre-MOX days, but including the metadata keys CFBundleExecutableCFBundleName, and CFBundleDisplayName don’t have any noticeable effect. Any tips in this regard would be greatly welcomed.

I had also attempted to get the pre-processor to generate the bundle identifier with “Mori-$(CONFIGURATION)” that fit whatever build configuration was in effect automatically, which would’ve avoided the use of the #if defined directive. Unfortunately, because the macro expansion would generate Mori-Release that method proved ineffective.

A corresponding idea is to use an alternate icon (via the CFBundleIconFile specifier) to represent the test version of your app. It helps you and your testers realize when odd behavior is due to running the wrong build just by looking at the dock or application-switcher. It’s also fun to double-click a document only to realize the test app is opening vital data meant only for the stable version. Hilarity is sure to ensue. But I’m a professional, don’t you kids try this at home!

If you don’t have the construction guy handy, you can resort to the technique I used before I discovered Info.plist processing: MOX’s own stamping of missing dock files makes for a handy visual guide to your test app. To try it yourself, add the debug version from within your build/Debug folder to your dock items. That’s right, the debug version (or whatever you use for test builds). Now delete it and empty the trash. (You will be building new ones, won’t you?) Now click on the app icon you just added to the dock. It adds a big fat ‘?’ to your lovely icon, doesn’t it? (At least it should if you deleted the correct icon.) Now rebuild your app and run it from within Xcode.

Now bring up the application switcher (cmd-tab). What do you see? A big fat ol’ ‘?’ emblazoned on the debug version of your app! Oh, you don’t? You see the normal icon? Yeah, you’re on Leopard, aren’t you? This trick doesn’t work as well on Leopard because MOX validates the file state more often than Tiger did. Such as, starting the test build from the Dock instead of only within Xcode. On Leopard, clicking on the dock icon when there’s a built debug version of your app in the debug folder will restore its unstamped icon. But anytime the question mark goes away, just delete the debug version, empty the trash, and click on the dock icon again.

Have fun, and keep ‘em flying!

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