Language and Computation

I just spent several hours (or at least it felt like several hours!) in frustration, searching a trivial bug. I’ve been testing a quick’n'easy prototype screen with an UIImageView and four UIButtons. The buttons are linked via an action to a view controller. And every time I press a button, my app conks out complaining that -[UITextEffectsWindow buttonPressed:] was an unrecognised selector. I checked the memory address, and it said it was my view controller, just before that exception was thrown.

I was ready to put the blame on some mistakes with Interface Builder, until I came across the solution (indirectly) in a blog: here the problem described related to properties, and the difference between “vc = …” and “self.vc = “. I had another look at my code and quickly found the offending line: I had the view controller as a local variable in the app delegates viewDidLoad method, and I autoreleased it. In other words, by the time the button was pressed the view controller no longer existed, and hence I got that weird error message.

This was not helped by the fact that UITextEffectsWindow is not mentioned in the documentation anywhere, as it seems to be an internal UIKit class, but at least it appears to be consistent.

So, if your button presses send messages to UITextEffectsWindow, make sure to check that your view controller is still alive!

DAY 11 and the pace is picking up. I managed to sort out two of the four tabs of the app, one including a table display of Esperanto/English dictionary entries (with the proper Esperanto diacritics), and the other one being a live-search on the English gloss entries. This one even pops up an automatic keyboard when first selected; the tab bar controller sends it a message when it has been activated. I even managed to answer a question on stackoverflow.com on that issue.

I also found somewhere a hint on how to automatically shrink the label size if the text is too long, wrote a converter from the Esperanto x-notation to unicode, etc. Really pleased! Both of these will appear here later.

One thing I don’t like too much is writing all the UITableViewDelegate methods when using a table. Quite a lot of boiler-plate code, but then, it is quite powerful. I just couldn’t be bothered writing yet another set of those methods for the final tab, the info view part. But there is nothing technically difficult with it. Objective-C is also getting easier and easier, and the auto-completion feature and API doc integration of XCode really helps. Though I think for serious code I will still use vile…

That leaves pretty much only the core part of the app: the Esperanto morphological analyser. I will implement this as a finite state machine, and working with Cocoa has given me the idea to implement it using delegates; an abstract hull which calls methods on the delegates whenever it needs to retrieve data, or match something. I have the feeling that this is pretty similar to Erlang’s OTP frameworks.

It is a really rewarding experience to see your own app on the iPhone. If only I was better at designing the tab bar icons! And I can already foresee one objection: one of the tabs has a star icon, the star being the Esperanto symbol. I think I need to change that, as the star is reserved for the ‘favourites’ meaning, and I don’t think Apple would appreciate the use of a star (even if it looks slightly slimmer) with another meaning.

DAY 10, and a little bit of progress. I found one error, which was about to drive me mad, until I more or less by accident stumbled over the solution on stackoverflow.com; in answering a slightly different question, Rob Napier commented on a bug in the way NSLog() was used.
NSLog(@"Returning %@ rows", [nodes count]);
Here, the -count method returns an int, but the %@ symbol expects an object. Result: a bus error. You need to use %d instead. And here was I, thinking how great it is not to bother with the old printf format codes, using the %@ way instead. I hate the primitive type/object distinction!

I then also found that I had created two superimposed Table Views (did I mention that I don’t really like Interface Builder after all?), so that my table got overwritten and looked all wrong. Now I’m struggling with getting the table to start at the first entry, not the 35th (indexPath seems to start counting sections at 1, rather than 0), and all of a sudden my database won’t work.

Preparing a straightforward SQL statement suddenly fails. I did not change that part of the code, the database file is still the same as it used to be before the error occurred, and I did tell XCode to do a full clean. Still, the error remains.

Grmph.

DAY 9 and more frustration. My ViewControllers didn’t seem to be called, and NSLog messages I put in didn’t appear on the console. And the whole thing crashed without me knowing what was going on.

Having another look at my iPhone development book, I realised the first mistake: the TabBar Controller wasn’t aware of which controllers to call up for the various tabs, something you need to set up in Interface Builder. Still don’t really like that way of doing things, as the fact you’ve done it (or not, as the case may be!) is not easily transparent.

After completing the tab bar attributes, the log messages suddenly turned up, which was good, and it also doesn’t crash. Well, at least not where it used to crash. Now it crashes in the loop where I read stuff out of the SQLITE database, and it crashes after the second iteration. Wonder what the cause is. Probably memory management. Mixing Objective-C and plain C makes things a bit confusing. And I don’t like that NSString is an object you need to allocate, but NSInteger is basically just an alias for int, so a primitive data type rather than an object.

Anyway, more bug hunting coming up. It all feels terribly slow, but then I’m only spending a few hours every couple of weeks on it at the moment.

DAY 8 and after a long pause I have been able to spend a bit more time on my project. And it was certainly frustrating, racking up the hours while trying to work out why it didn’t work. One thing I need to get used to are IDEs; more than a decade of simply editing code in vi and compiling it on the command-line leave you ill-prepared for working with XCode, nice though it may be. Interface Builder is also a great tool, but it hides things from direct view or easy inspection, at least if you don’t know where to look. And then something doesn’t work because you omitted a link from a View to its File Owner, or you set the base class of MainWindow.xib to a wrong class type.

After trying out some table code in the iPhone Development book I finally got a small demo going. I’m now trying to create an indexed grouped table display backed by a sqlite database working. But now it’s approaching midnight and I’m too tired to work out why it stopped working again…

However, despite all of today’s frustration, I’m getting more and more used to coding in Objective-C, which has to be a positive side-effect!