maemo.org - Talk - How to compile Qt location example ?

Quote:

Originally Posted by bartenst (Post 615319)

@multisil: Have you been able to fix your problem with the segmentation fault?

Greetings,
bartenst

Yes. I have a solution for having QT Main Loop for UI and GTK+ loop for GPS device. The solution is to create a separate thread for GPS (as a QThread). In your main app you have to initialize the thread, but not actually start it before your QT main loop has started. So you have to post a QTimer event to your QT Main Loop to start the GTK+ loop. Also, you have to take care of closing the thread when your app is closing, so you have to implement a method for this in you main app class.

So my main.py would be (I suppose you have a simple QT Designer created UI file my_ui.py with one button (myBtn) and text label (msgLabel)):

Code:

import sys

from my_ui import *

from GPSConnection import *



class myWindow(QtGui.QMainWindow):



#

# Constructor

#

    def __init__(self, parent=None):

      super(myWindow, self).__init__()



#

#  UI myBtn button click handler.

#     

    def myBtnClicked(self):

        if self.gps.fix:

            msg = "Lat: " + str(self.gps.lat) + " Lon: " + str(self.gps.lon)

            self.ui.msgLabel.setText(QtGui.QApplication.translate("MainWindow", msg, None, QtGui.QApplication.UnicodeUTF8))



#

# Application is about to close. We have to clean up the GPS related things, namely

# close the GPS device and quit the GPSConnection thread.

#

    def closingApp(self):

        print "Closing..."

        if self.gps.running:

            self.gps.control.stop()

            self.gps.loop.quit()

       

#

# Handler for a timer event that should happen when the QT Main Loop has started.

# We can safely start the GPSConnection thread, that has its own GTK+ event loop.

#              

    def singleUpdate(self):

        print "Start timer"

        if self.gps.running == False:

            self.gps.run()



#****************************************************************#

#* MAIN APPLICATION                                             *#

#****************************************************************#



#       

# We instantiate a QApplication

#

app = QtGui.QApplication(sys.argv)

MainWindow = myWindow()

MainWindow.ui = Ui_MainWindow()

MainWindow.ui.setupUi(MainWindow)

MainWindow.gps = GPSConnection(app)

MainWindow.show()



#

# Timer for launching the GPS when app starts. The GPSConnection can not be started

# before the QT Main Loop, so this ensures that it starts after we have started

# processing events in the QT Main Loop. GPSConnection class uses GTK+ main loop

# and that is just ok, since we are running GPSConnection in its own thread.

#

gpsLaunchTimer = QtCore.QTimer()

gpsLaunchTimer.singleShot(1000, MainWindow.singleUpdate)



#

# Signals that enable us to catch the event when app is closing 

# so we can close the GPS device and thread. We propably do not need both.

#

QtCore.QObject.connect(app,QtCore.SIGNAL("aboutToQuit()"), MainWindow.closingApp)

#QtCore.QObject.connect(app,QtCore.SIGNAL("lastWindowClosed()"), MainWindow.closingApp)



# 

# Now we can start the UI & QT Main Loop.

#

sys.exit(app.exec_())

and GPSConnection class in GPSConnection.py:

Code:

import os

import location

from PyQt4 import QtCore

import gobject



# This class implements a GPS connection class to the gps device.

# The class can be safely used in QT applications, because this

# class is supposed to be running in its own thread. Also, the

# class implements its own GTK+ event loop.

#

# The GPSConnection thread must not be started before the QT Main

# loop. Instead, use QTimer to generate a start event for the 

# GPSConnection thread. This way, the even is prosessed

# in the QT Main Loop after the loop has been started.

#

# Also, you should implement closingApp method in your QT main loop 

# (in you main window QObject) that takes care of shutting down the 

# GPS device and stops the GPSConnection thread.

#

class GPSConnection (QtCore.QThread) :



#

# Constructor

#

    def __init__(self, app, parent=None):

        super(GPSConnection, self).__init__()

        self.control = location.GPSDControl.get_default()

        self.GPSDevice = location.GPSDevice()

        self.control.set_properties(preferred_method=location.METHOD_USER_SELECTED, preferred_interval=location.INTERVAL_DEFAULT)

        self.GPSDevice.connect("changed", self.onChanged, self.control)

        self.control.connect("error-verbose", self.onError, self)

        self.control.connect("gpsd-stopped", self.onStop, self.control)

        self.lat = 0.0

        self.lon = 0.0

        self.fix = False

        self.running = False

        self.app = app

        self.loop = None

 

#

# GPS error callback handler

#

    def onError (self, control, error, data):

        print "location error: %d... quitting" % error

        self.running = False

        

        if error == location.ERROR_USER_REJECTED_DIALOG:

            print "User didn't enable requested methods"

        elif error == location.ERROR_USER_REJECTED_SETTINGS:

            print "User changed settings, which disabled location"

        elif error == location.ERROR_BT_GPS_NOT_AVAILABLE:

            print "Problems with BT GPS"

        elif error == location.ERROR_METHOD_NOT_ALLOWED_IN_OFFLINE_MODE:

            print "Requested method is not allowed in offline mode"

        elif error == location.ERROR_SYSTEM:

            print "System error"

    

#

# Handler for stopping the GPS device.

#

    def onStop (self, control, data):

        if self.running:

            self.running = False

            print "In onStop method"

            data.stop()



#

# Callback handler for the event when location fix has changed.

#    

    def onChanged (self, device, data):

        print "In inChanged method"

        if not device:

            return

        if device.fix:

            if device.fix[1] & location.GPS_DEVICE_LATLONG_SET:

                self.lat = device.fix[4]

                self.lon = device.fix[5]

                self.fix = True

                    

#

# Start the GPS device.

#

    def start_location(self, data):

        data.start() 

        return False



#

# Start the GTK+ main loop. The loop initializes the start_location callback which actually

# runs the GPS device.

#

    def run(self):

        print "In run"

        self.running = True

        self.loop = gobject.MainLoop()

        gobject.idle_add(self.start_location, self.control)

        self.loop.run()

Hope this helps!