Threading in PyQt

Question

I am developing a software which has a virtual piano and that can be controlled by a midi keyboard. What I'm trying to do is I want a thread watching the midi inputs ans when there is a data coming corresponding process should be triggered ( here playing the sound and animating the key). How can I do it with Qt Threading and events?

Answer 1

Here is a good page on how to use custom signals: http://www.riverbankcomputing.co.uk/static/Docs/PyQt4/html/new_style_signals_slots.html

• Old style: http://pyqt.sourceforge.net/Docs/PyQt4/old_style_signals_slots.html
• New style: http://pyqt.sourceforge.net/Docs/PyQt4/new_style_signals_slots.html

And here is a page showing how to use QThread: http://joplaete.wordpress.com/2010/07/21/threading-with-pyqt4/

Thats pretty much all you need. You create the QThread with a run() function that will loop and monitor your midi port, and then emit a custom signal. You would start this thread with your application launch. And you would connect the QThread's custom signal that you created to a handlers on your main app or whatever widget should be notified.

Answer 2

Here you have small example:

import time
import sys

from PyQt4 import QtCore, QtGui
from PyQt4.QtCore import SIGNAL, QObject


class DoSomething(QtCore.QThread):
    def __init__(self):
        QtCore.QThread.__init__(self)

    def run(self):
        time.sleep(3)
        self.emit(SIGNAL('some_signal'))


def signalHandler():
    # We got signal!
    print 'Got signal!'
    sys.exit(0)

if __name__ == "__main__":
    app = QtGui.QApplication(sys.argv)

    # Create new thread object.
    d = DoSomething()

    # Connect signalHandler function with some_signal which 
    # will be emited by d thread object.
    QObject.connect(d, SIGNAL('some_signal'), signalHandler, QtCore.Qt.QueuedConnection)

    # Start new thread.
    d.start()

    app.exec_()