Expanding Outline Views in Cocoa

Thanks to a lengthy commute last week, I’ve been making a toy in Cocoa. It reads an URL, parses some XML and displays it in an NSOutlineView. Simple stuff, but it will hopefully make my life better at work, where I need to do this a fair bit.

By default, when I load the XML into the NSOutlineView, everything is closed up. So all you’re presented with is the root element. I’d like to expand that so it automatically includes all children of the root element. Nice and simple—there’s an expandItem: method.

Except that when I call it from the action that puts the XML into the NSOutlineView, it doesn’t work. Bugger.

After instrumenting my XML data source, I can see that nothing is really happening until after my action. My suspicion is that the NSOutlineView isn’t realising that it has any data until after the first call to display.

I tested this by hooking up the call to expandItem into a secondary action (on another button). And it works great.

So, I need a way to say “call this code back in the next idle period”. And this is where I start to get upset that Objective-C doesn’t have closures.

How to execute code soon isn’t easily determined from the apple docs. My guess is that you use an NSTimer with a very small NSTimeInterval . Let’s try that…

  NSTimer *idle = [NSTimer scheduledTimerWithTimeInterval:0.0
  [[NSRunLoop currentRunLoop] addTimer:idle forMode:NSDefaultRunLoopMode];

Well, it works. But! Further investigation finally reveals Deferring the Execution of Operations. This suggests that I should use an NSNotification instead, but posted with a NSPostWhenIdle flag. This means getting involved with the cocoa notifications system

The code now ends up looking like this:

  - (void)awakeFromNib
    // Listen out for notification's we've posted to ourselves.
    [[NSNotificationCenter defaultCenter] addObserver:self

  -(IBAction)fetch: (id)sender
    // …
    NSNotification* todo = [NSNotification notificationWithName:@"expandRoot"
    [[NSNotificationQueue defaultQueue] enqueueNotification:todo

  - (void)expandRoot:(NSNotification *)notification
    [outlineView expandItem:[[outlineViewDataSource doc] rootElement]];

Which is quite a bit more code. But it feels more robust doing it this way.

The big take away from all this is how difficult it is to use a non-Open-Source framework. If I had the source to Cocoa, I’d be able to look inside and see what I needed to do simply and quickly. Instead, it took me three train journeys. But there’s still enough to like in Cocoa that I intend to carry on.



I hate maven. The UI sucks so badly, it’s incredibly painful to use. Anything that can take the edge off this has to be a good thing. In the past, I’ve experimented with m2eclipse, but to be quite frank, it’s not much improvement over the command line. And the tools are why we use Java instead of Perl/Python/Ruby, right?

So now I’m trying out q4e, which is being promoted as the “official” maven integration for Eclipse. At some point. Hopefully.

After installing (0.4.0), first impressions are good. There’s a “new maven project” wizard, which knows about archetypes. Creating archetypes manually is incredibly annoying (I can never remember how). Now, the wizard just lists them for you:

The q4e archetypes wizard

Afterwards, it nicely prompts you for details like groupId and artifactId. Plus a description, which I’d never have thought of otherwise. The more metadata the better! (Actually, the description appears to vanish once the project has been created).

Once created, this is what you end up with.

A new maven project created by q4e

Nice and simple so far. Most of the maven commands are on the right-click menu:

q4e's main menu

When you run something, you get a log viewer, which is a little nicer than the m2eclipse console. At least it’s timestamped.

The q4e log view

Unfortunately, the dependency management appears to be broken. I can’t search for dependencies in the way I could in m2eclipse. That’s not good, as there are lots of them available and the computer should be telling me what the heck they are.

Annoyingly, it seemed to “lose” my src/main/java folder. I had to recreate it in order to get it to work. Very odd.

It will graph dependencies, which is probably more useful on a larger project than my test app.

The q4e dependency viewer

There’s no help yet, which is annoying, though not critical (I don’t know anyone who uses Eclipse help much anyway. Developers—who’d believe it, eh?)

The one thing that’s been really bugging me with maven is the complete inability to get at the source code of dependencies. Oh sure, it’s available for download, and there are features to ask for the source to be downloaded. But I have no idea how on earth to make it work. Not having source code is a real problem when it comes to understanding software.

It didn’t offer much help in the way of creating tests (A default src/test/java would have been nice).

Overall, it’s pretty clear that this is a very early stage of development. But it still looks more promising than m2eclipse, and anything that can make maven easier to use is most welcome.

That was all written last night. This morning, I’ve updated to the development build (0.5.0). It’s managed to grow a “Fetch Source JARs” command, which is great. Unfortunately, I’ve just bumped into issue 153—the compiler settings aren’t synced between maven and eclipse. Oh well. I stand by the previous paragraph. This has potential, but it’s not there yet.