Qt DevDays 2010

I'm attending Qt DevDays 2010 and really looking forward to it.

I haven't decided yet which tracks I'll attend, there are so many interesting but I definitely go for some Quick-talks. I believe I'll have a great time.

And that's not all, in November I'll also attend a two day Mobile Qt course at Öredev with topics such as Qt Mobility API, Gesture framework, Hybrid JavaScript apps and last but not least Quick. Looks very promising.

PyQt and Signal overloads

I almost spent half an hour trying to figure out why my code didn't work.

I used a QSignalMapper to connect a couple of clickable widgets to emit just one signal, widgetClicked(int index), instead of having multiple signals, one for each widget. I connected the widgetClicked signal to the mapped signal of the QSignalMapper class and did the required set up for the signal mapper, something like the following snippet:

self._signalMapper = QSignalMapper(self)
self._signalMapper.mapped.connect(self.widgetClicked)

for index, widget in enumerate(buttons):
    widget.clicked.connect(self._signalMapper.map)
    self._signalMapper.setMapping(widget, index)

Everything worked fine until I changed the signature of widgetClicked to pass a string instead of an int, it didn't work anymore. I only got the following print out: TypeError: connect() failed between 'mapped' and 'widgetClicked' and had no clue why because the mapped signal has a couple of overloads:

void mapped(int i)
void mapped(const QString & text)
void mapped(QWidget * widget)
void mapped(QObject * object)

I did also try changing widgetClicked to not receive any arguments and that worked, which was expected because the receiver is not required to match all arguments of a signal. Of course, it also worked if I changed back to int...

What the #@! is going on? Naturally, I had no option of searching for answers since I was sitting on the train back home from work and had no Internet connection.

Then it come to me, Python is not aware of the C++ signature overload. Python doesn't support overloading. Python/PyQt can't set up the right connection between widgetClicked and mapped. But how do you specify which of the overloads you want to connect to? By indexing:

# This connects your slot/signal to the string-overload
signalMapper.mapped[str].connect(...)

The int overload will be used default by PyQt, that's why my code worked when I connected widgetClicked to mapped w/o specifying which overload I wanted.

IcecastRadio - Qt widget/Qt Quick example Icecast player

I've been toying with modeling a Qt application which supports both a traditional widget-based view and a quick-based (qml) view.

About IcecastRadio
The intention of this project/application is to demonstrate how important
it can be to design a model for your application. If the model is correctly
designed, it can be used from both traditional widget based UIs and
modern UIs built with Qt Quick without too much effort.

The advantage is of course that you can provide both a desktop application which integrates with the native look and feel of the OS and at the same time have a totally different experience UI-wise, for example in an embedded device by only changing the view-layer.

IcecastRadio is actually two applications, QtCast and QuickCast. QtCast implements the widget-based view and QuickCast the quick-based view. Both application depends on a third entity, the model. You'll see this division in the source code in form of three projects, qtcast, quickcast and model.

The application was successfully compiled against Qt 4.7-beta 1 and 2.

Source code
You'll find the source code at http://gitorious.org/icecastradio. The player code is released under the MIT license, clone and have fun. Please read the README file found in the repository for more information.

Screenshots
Must have...

Remark
The application lacks a lot of features that could be expected from a radio player, for example there is no way of sorting the list of stations nor any filtering can be applied. The intention was not to create a full blown Icecast player but to demonstrate how to create a model that is usable from both a widget-based application and a quick-based application.

Patches are welcome :)

Python Koans - A Great Way to Learn Python!

I just found out about Python Koans by Greg Malcolm (thanks dude) after listening to the from python import podcast podcast (which I find amusing, thanks guys).

It's an awesome way to learn Python. Instead of just reading tutorials and/or books you learn Python by coding.

The interactive tutorial is built around unit-tests and you advance and gain new skills by passing tests and it's really funny. You do learn a lot about the Python language when doing the Koans so I recommend it even if you've been using Python for a while.

Another cool thing is that you learn how to do unit testing in Python, if you're not already familiar with it.