Thanks to Tom Hesser for inviting me to be on the show. It was a blast!

I had just done a build, tried to load the Desktopple Pro preference pane to test it, and, for some strange reason, it wouldn’t load. A quick check of the Console log revealed this rather terse error message:

Can't cache image

I tried a fresh build, and I got the same error. Puzzled, I then turned to Google. A search revealed a lot of hits for that phrase, but no real answers on the cause or the solution.

Worse, the bugs I had been working on were in the Desktopple app, not the preference pane, so the problem wasn’t a result of a code change, but something that was already there!

Fortunately, after a few hours of pulling out my hair, I finally figured it out. And since Google didn’t help, and there really weren’t any solutions out there, I’m posting mine. Hopefully, it will save others the frustration of trying to figure out this unhelpful error message.

Turns out that if you -lockFocus on an NSImage with either a zero width or a zero height, you’ll get the “Can’t cache image” error (other issues may cause it as well).

The solution is easy: before locking focus on the image, make sure the image has non-zero height and width.

Look for this fix (as well as a couple others in Desktopple Pro) in a day or so.

Scott does a fantastic job of presenting complex concepts in easy-to-understand ways, and if you are interested in getting started in Mac/Cocoa programming, I recommend his tutorials without hesitation. In fact, when I was just learning, Scott’s Cocoa site, CocoaDevCentral, was instrumental in so many ways.

Great job, Scott!

As promised, I’ve been working to solve this, and it seems that the problem lies within the Desktopple Preferences. Basically, if you lauch Desktopple Pro and don’t open Upon further digging, the source of the memory usage is in Apple’s bindings technology. To be honest, I don’t know whether it’s an Apple bug or a me bug, but it’s definitely a bug.

In any case, the solution I came up with was bigger than I intended. One of my biggest feature requests since Desktopple Pro was released was to make it a Preference Pane app instead of a menu bar app. This has the advantage of still letting Desktopple Pro do its magic while removing the icon from the menu bar. You’ll be able to choose whether you want to see the menu bar icon, so those with small screens will really appreciate the regained real estate, while those with larger screens will still be able to show the icon in the menu bar.

The upshot is that I’m still working on it. I’ve got another day or two worth of work, then a few days for testing, so I hope to have a release early next week.

In Leopard, Apple nicely included a little command line utility that takes two TIFF images of differing resolutions and combines them. It first checks to see if the images can be combined (making sure the resolutions match up, etc.). It then compresses the resulting combined image. The problem with the utility is that it’s command line based, so you end up doing a lot of needless typing.

While working to update some of my apps to include resolution independence, I found myself dropping into the command line a lot. To save time, I whipped up a little utility called TIFFer. It’s basically a wrapper around the Apple utility, but I find it fits into my workflow much better. It’s freeware for any developers who might need it, so get it now.

[Caveat Emptor: This is a Leopard-only app, and I've only tested it on my machine. If it doesn't work for you (and you're running Leopard), please let me know.]

Desktopple is a menu item that will let you quickly hide your entire Desktop. It’s free (donations gratefully accepted), but it also hasn’t been fully tested, so consider it Beta, please. Web 2.0, here I come!

Here’s the link: Desktopple.

Enjoy!