From This Day

Those who ever happened to write an application for Mac have to realize the existence of Property List files – for storing user’s settings and defining details on app’s behavior inside the OS. For example, if you want your application to be an agent, i.e. run without menu bar and Dock icon, you set the appropriate flag in the Info.plist file inside the application bundle:

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<key>LSUIElement</key>
<true/>

Fair enough, if you’re an Objective-C Cocoa developer. But if you’re, let’s say, a C++ Qt programmer deploying your app on Mac OS X as yet another platform, you can end up with such a flood of (probably) unexplainable errors:

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ayoy@batory repo % ./qtwitter.app/Contents/MacOS/qtwitter
2009-02-22 00:14:40.420 qtwitter[46617:10b] *** _NSAutoreleaseNoPool(): Object 0x1315f30 of class NSCFString autoreleased with no pool in place - just leaking
Stack: (0x9330173f 0x9320de32 0x92f1f1b1 0x92f1f21d 0x92f1f271 0x92f1d90c 0x92f1d9d2 0x92eb5b17 0x3d1f2b 0x9a3e08 0x94fd23 0x950096 0x6b64 0x653b 0x6469)
(... boooooring ...)
2009-02-22 00:14:40.428 qtwitter[46617:10b] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '*** -[NSCFBoolean length]: unrecognized selector sent to instance 0xa03d8400'
2009-02-22 00:14:40.429 qtwitter[46617:10b] Stack: (
2465300747,
2491215419,
2465329930,
2465323276,
2465323474,
2464897815,
4005675,
10108424,
9764131,
9765014,
27492,
25915,
25705
)
zsh: trace trap ./qtwitter.app/Contents/MacOS/qtwitter

Not that I dislike Macs, but that’s really uncool. Strictly speaking, the program is failing badly when trying to create an instance of QApplication. And this applies at least to Qt 4.4.3 and, as I suppose, the previous releases too. Now here comes the good news — we already have a release candidate of Qt 4.5, which can cope with the LSUIElement setting. So if you experience such a problem, just switch to the newest Qt available, it should be stable enough in most cases. And if you’re afraid of release candidates, just wait these few days until it becomes official.