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POAre Singletons EVIL in GUI Programming with Qt?
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copied!<p>I'm just starting my first fairly large Qt project which will be mostly a bunch of screens with buttons, tab widgets, and Qwt Plots. The panel stack pattern described in <a href="http://doc.trolltech.com/qq/qq27-panelstack.html" rel="nofollow">Qt Quarterly 27</a> seems pretty nice for my application. Each of my screens is a QWidget encapsulated in a Panel which is shown/hidden by a QStackedWidget. However it uses a <strong>singleton pattern</strong> for each Panel so that they aren't all created immediately as the app starts and so that more than one of each screen isn't ever created. </p> <p>So I started coding. Got the panel stack working. Added some code so that dynamically updating widgets aren't dynamically updating all the time. Got my history stack/back button working for the panels. Everything seems just fine, but I've got one nagging worry:</p> <ol> <li>My code smells.</li> </ol> <p>I am in no place to argue with any of the hate posted here and on blogs about the singleton pattern. I think I get it and the code I've written does make me feel a bit dirty with all the boilerplate lines and global objects. But I do like not having to worry about whether or not I already instantiated a screen before switching to it and adding it to my history stack. I just say switch to that screen, it's added to my history stack, and the magic works.</p> <p>From what I've read there are also some cases where singletons can be worthwhile. Is this one of those special cases? The magic screen switching / history stack makes me think 'yes' but the sheer number of different singleton classes I'm going to have to create makes me think 'NO no NO NO NO'.</p> <p>I want to just man up and figure out how to get the singleton pattern out of my code <strong>now</strong> so that I don't have to do it later. But I don't want to get rid of all my singleton classes just to get rid of my singleton classes because they're EVIL [citation needed].</p> <p>Any input is much appreciated!</p>

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