Debugging with backups

If you’ve written an application for the iPhone, you’ll eventually encounter a customer problem that you can’t reproduce. Of course, you’ll want to get a copy of the customer’s data and preferences so you can replicate the environment they are working in. And then you’ll realize that it’s a total pain in the ass for both you and your customer.

iTunes creates backups every time a user syncs their device, but these backups are meant to be read by a machine, not a human. Your customer will have to wade through a bunch of GUIDs in the MobileSync/Backup folder: getting the right backup for your application has been a headache.

Fortunately, things got much better last week with the release of Pádraig Kennedy’s iPhone Backup Extractor. Pádraig is the author of the Python script some of us have been using to extract data from the .mdbackup files. Having this script in a GUI that the end user can run is a huge improvement.

You can instruct your customer to download the application, sync their device with iTunes and then have them select the latest backup and your application within that backup. The resulting output contains the documents and preferences in use by the application at the time it was synced and can easily be put in a ZIP archive.

Getting this information into your development environment is then just a matter of hacking around with the Simulator folder structure in ~/Library/Application Support/iPhone Simulator/User/Applications. The bug won’t stand a chance at this point :-)

Thankfully, Pádraig has made this a free application. Your customers won’t need to pay for anything before they help you out. You, on the other hand, won’t be using it directly but will still benefit immensely. Make sure to click on the Donate button so that this application will continue to see development and maintenance. I just did.

Splash screens

Twitterrific has a splash screen and I would like to get rid of it. But I can’t.

Splash screens hurt the user experience from a purely psychological point-of-view. They don’t change the launch time of your iPhone application at all, but it looks and feels longer.

But there’s a problem: you can only specify one Default.png file to be displayed at launch time. Unfortunately, applications can have many visual states which you’d like to show as the code is loaded. In the case of Twitterrific, the list or detail view can be active and they have no visual commonality.

So what are the current options?

Some people have suggested that you have a single startup image (like the list view in Twitterrific) and use a Core Animation transition to the actual state the user was last in. This would work, of course, but it has a major flaw: it increases the amount of time needed before the user can actually start using the application (they need to wait for the transition to finish.)

Another option would be to show a blank screen. I tried this, and my first thought was that the application had crashed. Not acceptable.

Why not replace the Default.png on-the-fly? As Tom Insam notes, you can’t modify the application bundle: doing so breaks the application signing and will leave you with code that won’t run.

So that leaves us with splash screens. The user knows the launch is in progress, there are no jarring visual changes, and it’s the quickest way to get to an active state.

Of course, there are mechanisms to have multiple startup screens. You can see it in the Clocks app: the world clocks view has a different startup image than the stopwatch view. Another example are the new chrome-less Safari pages that you can put on the home screen: these apps take a snapshot of the current screen at exit and display it at the next launch.

Apple should expose this functionality to third parties. If you agree, please submit a duplicate for Radar ID# 5872097. Until that happens, please excuse our splash screen.

Fancy UILabels

People have asked which part of our Twitterrific application for the iPhone was hardest to develop. There were many challenges, but the one I found most onerous was scrolling in the UITableView.

The code we shipped in 1.0 was obviously flawed. Scrolling was jerky. We weren’t happy with it and neither were users.

There was no shortage of “expert” opinions on what was causing it. Some thought it was the loading of the avatar images, others thought it was the fancy backgrounds. One reviewer on iTunes even suggested that I could spend a couple of hours reading documentation on Apple’s site and fix it up.

Yeah, right.

The root of the problem was having links inline with the text: there are currently no attributed strings in the iPhone SDK. Before displaying a table row, I had to scan the text of the tweet for URLs and screen names, measure the length of text, and then create a bunch of views that approximated what people were used to seeing as HTML. This overwhelmed the CPU on the device: the GPU was having no problem compositing the layers. I had heeded the advice of experts and was careful to flatten the hierarchy as much as possible and to use opacity sparingly: only NSString’s sizeWithFont: was killing me.

So what changed in the 1.1 release? A slight interaction change and a new approach to rendering the UIButtons used for the links in the text.

The interaction change was that no text was styled when a table row is unselected. This allowed us to use a plain UILabel for the text of the tweet. Since only one tweet is selected at any time, this simplified the text layout requirements when reusing a table row.

Since UILabel was being used for rendering the text, our approach for measuring text changed as well. Instead of controlling all the text layout, I had to adapt my code to use metrics and line breaking that matched those used in UILabel’s implementation. They call it reverse engineering, kids.

This approach is far from perfect. There are cases where the buttons are placed incorrectly: I suspect that the cause of these problems is how round-off error is being handled in the method used by UILabel’s underlying WebView and the method used by sizeWithFont:. A half-pixel being rounded up versus down can cause a line break or the button text to not align with the underlying label. These errors seem to occur more frequently with Asian fonts.

There is also an issue with a URL that wraps a line: the button is only created for the first part of the URL (leading some users to think that the button won’t work—it will.)

In essence, it’s a hack. And useful one until Apple deals with Radar ID# 5834539 (titled “There is no way to style a run of text in a UILabel or UITextView”.) It wouldn’t hurt to dupe it if you’d like to see this aspect of the iPhone SDK improve.

Now that the FABULOUS NDA is a thing of the past, there’s no reason why you should have to figure this stuff out like I did. Here’s my implementation. Knock yourselves out customizing this code for your own needs. All I ask is that if you make any improvements in createButtons:, please let me know (my contact info is on my résumé page.)

But wait, there’s more!

And an extra added bonus, this project also shows you how to use regular expressions using RegexKitLite and libicucore. Extra pattern matching goodness, for all your iPhone needs.

Damn it feels good to leave out that NDA disclaimer at the bottom of this essay.

Updated December 4th, 2008: In the original essay, I forgot to link to the RegexKitLite page at SourceForge. This code by John Engelhart is so damn useful, I tend to think about it as a standard part of OS X. Take a moment and check out this project’s exemplary documentation.


Thank God—that’s the last time I’m going to type that word for awhile. The meme is dead, long live the SDK.

As a way to celebrate the lifting of the NDA, we bring you some very special source code. To wile away the time between our product submission and the launch of the App Store, my buddy Anthony Piraino and I worked on this very special treat. Something that will be familiar to all developers who have had to keep their mouths shut since March 6th, 2008. Just compile the source code and install it on your device. Typing pleasures await.

(You’ll need to install Twitterrific from the App Store to get the full user experience. But you’ve done that already, right?)

Besides being a fun inside joke, this very special application also shows an important aspect of iPhone development: URL schemes.

As we’ve seen many other times, the needs of a mobile user are very different than those of a desktop user. On the desktop, tight integration of several application domains makes applications like Coda a joy to use.

On the phone it’s better to focus on one task. From what I’ve seen, the best iPhone applications do one thing and do it well. Supporting URL schemes in your application makes that single task more attractive to other developers and users. It leads to what my friend Daniel Jalkut has aptly called the “Un-Coda-fication” of iPhone apps.

The benefit for a developer is obvious: it minimizes the scope of an application and the attendant memory footprint. You could write your own Twitter update code using a NSURLConnection, or you could use one line of code like this:

[[UIApplication sharedApplication] openURL:[NSURL URLWithString:@"twitterrific:///post?message=EASY"]];

There is a less obvious, but equally important benefit when you look at URL schemes from a user’s point-of-view. Since your application’s scope is limited to one task, users will depend on it when they want to perform that task. Even if that task is in the context of another application.

An example of this is sharing photos. Users know that the Camera application takes pictures and that the Mail application sends messages. You don’t see a camera button in Mail; you see an “Email Photo” button in your Camera Roll. The user’s first task it to take a picture and the next task is to mail it.

Since we’re not Apple, we can’t achieve the high level of integration between the Camera Roll and the Mail application. But we can use URL schemes to accomplish much the same thing.

I worked with Fraser Speirs and Ian Baird during the development of Exposure and Cocktails so that their applications could support a “Post to Twitter” button. Clicking on that button initiates a workflow that lets the user share what they’re looking at on Flickr or what kind of drink they’re enjoying. Leaving their app/task and launching Twitterrific makes complete sense.

If you’d like to include a “Post to Twitter” button in your own application, all the code you need is in the postToTwitter: method in the very special application mentioned above. If you want to handle your own URL scheme, take a look at application:handleOpenURL: in the application delegate. Be careful about validating inputs: you don’t want malicious URLs to do bad things.

Not to dampen your enthusiasm, but please be aware of a couple of limitations with URL schemes. First, there is no way to know if a URL scheme is supported or not (rdar://problem/5726829). Currently, the best you can do is to performSelector:withObject:afterDelay: then openURL:. If the selector gets called you know that the URL failed to open. Also, be aware that deleting an application can sometimes leave the URL registration database in a state where it no longer recognizes a scheme (rdar://problem/6045562). This only happens when two applications support the same URL scheme, so you can avoid the problem by using a unique scheme name. Please use the Radar bug ID# for a “me too” bug report if this becomes a problem in your own application.

Now let’s enjoy our newfound freedom to discuss the iPhone SDK and the first of many sample code releases on this site!

Update October 1st, 2008: As Jonathan Rentzsch and Thomas Ptacek point out, URL schemes can be an attack vector for your application. Pay particular attention to the code in -application:handleOpenURL: in your application delegate. If you find any vulnerabilities in my code, please let me know so I can update this essay. Thanks!

Update October 7th, 2008: Once your application supports URL schemes, it’s likely that you’ll want to provide a bookmarklet in Safari. Here’s the one we use in Twitterrific:


The hardest part about doing this is guiding the user through the setup process. Joe Maller came up with a simple solution that lets the user get the Javascript into their bookmark list. This was later refined by Alexander Griekspoor. Make sure to view the source on these pages for additional hints and installation instructions.

If you agree that this setup process is too difficult for end users, please submit a duplicate bug for Radar ID# 5935641. Thanks!

Update February 4th, 2012: UIApplication now provides a -canOpenURL: method that lets you check if there is an application installed that supports the URL scheme.

Killing our enthusiasm

Dear Steve,

I am an iPhone developer. I love Cocoa Touch—it’s an amazing piece of engineering. I’m having great success with the products I’ve written (one of them even won an ADA at this year’s WWDC.) Sales through iTunes are great and well above my expectations.

And despite of all this, I’m feeling ambivalent about developing new applications for the iPhone.

Of greater concern is that I’m not alone: many of my colleagues are starting to feel the same way. To illustrate, here are some thoughts from people whose work I respect and admire:

Steven Frank – Panic (Transmit/Coda/Unison)

Fraser Speirs – Connected Flow (Exposure)

Wil Shipley – Delicious Monster (Delicious Library)

Brent Simmons – NewsGator (NetNewsWire)

You should also be aware that much of the discontent is being masked by the NDA that’s currently in place. I, and many others, do not want to anger Apple and there are no forums to voice our concerns privately.

As you’ve seen throughout your own career, great engineering is not driven solely by financial rewards. Woz didn’t write Integer BASIC by hand because he thought it would make him rich. Andy Hertzfeld’s and Bill Atkinson’s work on the original Mac wasn’t motivated by greed.

Great developers create amazing software for love as much as money. Take away the artistry and craftsmanship and you’re left with someone pumping out crapware for a weekly paycheck.

I have worked on many different platforms throughout the years: the most important benefit to working on the Mac is the vibrant community of developers. The high quality of Mac applications is due in large part to great developers being able to learn, compete, innovate, and share in a common success. This camaraderie sustains the love for the platform.

I was hoping the same would be true for the iPhone. Sadly, it’s not, and that makes this new platform really hard to love. I’m trying to stay positive in spite of recent developments, but I’m finding my attraction to the iPhone fades a little bit each day. I think it’s important that you know that.

Thanks for your time,

Craig Hockenberry

P.S. As I was writing this essay, Jason Snell and Dan Moren posted some articles at Macworld about the App Store and NDA. The disaffection is starting to spread outside the development community.

Update October 1st, 2008: Thank you.