PyQt Tips and Tricks

With Meego there is a lot of interest in developing applications in Qt rather than GTK. This page spawned from a discussion thread.

Contents

Tips and Tricks

Identifying the Sender of a Signal

There are two main approaches for this. The first is to wrap the slot with a lambda to pass in any additional arguments 

def notifyMe(foo)
  print foo
 
f = QPushButton("Click me!")
x = lambda: notifyMe("they call him tim")
self.connect(f, SIGNAL("clicked()"), x)

[1]

The second and more general solution is to use the QSignalMapper[2]

Learning to use Qt CSS

Much like web development, CSS is also available within Qt. There's a list of examples that can be tried out just using Qt Designer. If you're using custom CSS, using palette() in your CSS definitions will allow you to use colors that the theme already knows about. As an example, this is an easy way to get the default blue color on your buttons when you want that color.

Depending on your needs, there's a number of built-in icons that are available for use.[3]

Style sheets and the native QMaemo5Style do not mix very well, since Maemo 5 lays out and draws some widgets very differently (e.g. QRadioButton). We recommend using local style sheets on specific widgets only, instead of setting one via QApplication::setStyleSheet().[4]

QString and Python

I've had some unicode-relate issues when moving strings between python datatypes and Qt datatypes. Somehow, the unicode stuff would get lost. So, it's likely easiest (At least when you're new to python and Qt) to use QString and QStringList than their pure python counterparts.

If you're not bringing in data from anywhere else, this isn't that big of a deal, but if you're interacting with data from any other source, unicode is a pretty likely scenario these days.[5]

Just to note that, in my experience, locales fail to work with PyQt - QTextCodec.codecForLocale() does not return the correct codec, which also means QString's toLocal8Bit() and fromLocal8Bit() fail.

The python locale stuff works fine, but then you have the joy of converting between QString and python strings (which works perfectly when it does it implicitly, but an explicit conversion seems to go via ASCII unless you specifically tell it to use utf-8 instead). [6]

Qt and Threads

QThread

import threading

QTimer

Spread the work across multiple callbacks to allow the UI to remain responsive. See multiple QTimer types

Stacked Windows 

 class showWindowQtGui.QMainWindow):
    def __init__(self, parent=None):
        QtGui.QWidget.__init__(self, parent)
 
        self.ui = Ui_main_window()
        self.ui.setupUi(self)
        try:
            self.setAttribute(Qt.WA_Maemo5StackedWindow)
        except:
            pass

[7]

Example Applications

  • ncalc
  • nclock
  • maesynth
    • Uses QGraphicsView
  • maelophone
  • healthcheck
  • qlister
  • Gonvert (1.0+)
  • WifiEye
  • MaeGirls
  • pyPianobar
    • Threading and Qt
  • pyRadio
    • Threading and Qt

Web Resources

Retrieved from "http://bugs.maemo.org/PyQt_Tips_and_Tricks"