Difference between revisions of "Updating-QML-content-from-Python-threads"

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[[Category:LanguageBindings::PySide]]
+
 
 +
[[Category:PySide]]
 
[[Category:snippets]]
 
[[Category:snippets]]
 
[[Category:Developing_with_Qt::Qt Quick]]
 
[[Category:Developing_with_Qt::Qt Quick]]
 
[[Category:Developing_with_Qt::Qt Quick::QML]]
 
[[Category:Developing_with_Qt::Qt Quick::QML]]
 
[[Category:Developing_with_Qt::Qt Quick::Tutorial]]
 
[[Category:Developing_with_Qt::Qt Quick::Tutorial]]
[toc align_right="yes" depth="3"]
 
  
= Updating QML content from Python threads =
 
  
 
This [[PySide]] tutorial shows you how to use native Python threads (non-QThread, i.e. '''threading.Thread''') to carry out work in the background (e.g. downloading files). In the special case of downloading, you might want to use '''QNetworkAccessManager''' and friends, but in this case, we assume that you can't use it for whatever reason (e.g. because you want to use Twisted or because you already have your special download code that you want to reuse).
 
This [[PySide]] tutorial shows you how to use native Python threads (non-QThread, i.e. '''threading.Thread''') to carry out work in the background (e.g. downloading files). In the special case of downloading, you might want to use '''QNetworkAccessManager''' and friends, but in this case, we assume that you can't use it for whatever reason (e.g. because you want to use Twisted or because you already have your special download code that you want to reuse).
Line 31: Line 30:
 
<code>
 
<code>
 
class Downloader(QtCore.QObject):
 
class Downloader(QtCore.QObject):
def ''init''(self, url, filename=None):
+
    def __init__(self, url, filename=None):
QtCore.QObject.''init''(self)
+
        QtCore.QObject.__init__(self)
self._url = url
+
        self._url = url
if filename is None:
+
       
filename = os.path.basename(self._url)
+
        if filename is None:
self._filename = filename
+
            filename = os.path.basename(self._url)
self._progress = 0.
+
           
self._running = False
+
        self._filename = filename
self._size = -1
+
        self._progress = 0.
 +
        self._running = False
 +
        self._size = -1
 +
 
 +
    def _download(self):
 +
        def reporthook(pos, block, total):
 +
            if self.size != total:
 +
                self._size = total
 +
 
 +
            self.on_size.emit()
 +
            self.progress = float(pos * block) / float(total)
 +
            urllib.urlretrieve(self._url, self._filename, reporthook)
 +
            self.running = False
  
def _download(self):
+
    @QtCore.Slot()
def reporthook(pos, block, total):
+
    def start_download(self):
if self.size != total:
+
        if not self.running:
self._size = total
+
            self.running = True
self.on_size.emit()
 
self.progress = float(pos*block)/float(total)
 
urllib.urlretrieve(self._url, self._filename, reporthook)
 
self.running = False
 
  
&amp;#64;QtCore.Slot()
+
        thread = threading.Thread(target=self._download)
def start_download(self):
+
        thread.start()
if not self.running:
 
self.running = True
 
thread = threading.Thread(target=self._download)
 
thread.start()
 
  
def _get_progress(self):
+
    def _get_progress(self):
return self._progress
+
        return self._progress
  
def _set_progress(self, progress):
+
    def _set_progress(self, progress):
self._progress = progress
+
        self._progress = progress
self.on_progress.emit()
+
        self.on_progress.emit()
  
def _get_running(self):
+
    def _get_running(self):
return self._running
+
        return self._running
  
def _set_running(self, running):
+
    def _set_running(self, running):
self._running = running
+
        self._running = running
self.on_running.emit()
+
        self.on_running.emit()
  
def _get_filename(self):
+
    def _get_filename(self):
return self._filename
+
        return self._filename
  
def _get_size(self):
+
    def _get_size(self):
return self._size
+
        return self._size
  
on_progress = QtCore.Signal()
+
    on_progress = QtCore.Signal()
on_running = QtCore.Signal()
+
    on_running = QtCore.Signal()
on_filename = QtCore.Signal()
+
    on_filename = QtCore.Signal()
on_size = QtCore.Signal()
+
    on_size = QtCore.Signal()
  
progress = QtCore.Property(float, _get_progress, _set_progress,
+
    progress = QtCore.Property(float, _get_progress, _set_progress, notify=on_progress)
notify=on_progress)
+
    running = QtCore.Property(bool, _get_running, _set_running, notify=on_running)
running = QtCore.Property(bool, _get_running, _set_running,
+
    filename = QtCore.Property(str, _get_filename, notify=on_filename)
notify=on_running)
+
    size = QtCore.Property(int, '', _get_size, notify=on_size)
filename = QtCore.Property(str, _get_filename, notify=on_filename)
 
size = QtCore.Property(int, ''get_size, notify=on_size)
 
 
</code>
 
</code>
  
h3. Creating a new Downloader instance
+
=== Creating a new Downloader instance ===
 
 
 
As an example, we create a new Downloader here that downloads a kernel image for the N900 from the MeeGo repository:
 
As an example, we create a new Downloader here that downloads a kernel image for the N900 from the MeeGo repository:
  
 
<code>
 
<code>
downloader = Downloader('http://repo.meego.com/MeeGo/builds/trunk/1.1.80.8.20101130.1/handset/images/meego-handset-armv7l-n900/meego-handset-armv7l-n900-1.1.80.8.20101130.1-vmlinuz-2.6.35.3-13.6-n900')
+
downloader = Downloader
 +
('http://repo.meego.com/MeeGo/builds/trunk/1.1.80.8.20101130.1/handset/images/meego-handset-armv7l-n900/meego-handset-armv7l-
 +
n900-1.1.80.8.20101130.1-vmlinuz-2.6.35.3-13.6-n900')
 
</code>
 
</code>
  
h3. QApplication, QDeclarativeView and context properties
+
=== QApplication, QDeclarativeView and context properties ===
 
 
 
As usual, we simply instantiate a new '''QApplication''' and a '''QDeclarativeView'''. Our Downloader is exposed to the QML context by setting it as context property '''downloader''' on the rootContext of our view. We then simply load the QML file via '''setSource''', '''show''' the view and execute the application:
 
As usual, we simply instantiate a new '''QApplication''' and a '''QDeclarativeView'''. Our Downloader is exposed to the QML context by setting it as context property '''downloader''' on the rootContext of our view. We then simply load the QML file via '''setSource''', '''show''' the view and execute the application:
  
Line 111: Line 112:
 
</code>
 
</code>
  
h2. WorkingOnIt.qml
+
== WorkingOnIt.qml ==
 
 
 
This is the QML UI for our downloader example. The interesting parts here are:
 
This is the QML UI for our downloader example. The interesting parts here are:
  
Line 198: Line 198:
  
 
Save the files '''WorkingOnIt.py''' and '''WorkingOnIt.qml''' in the same folder and start the app using '''python WorkingOnIt.py''':
 
Save the files '''WorkingOnIt.py''' and '''WorkingOnIt.qml''' in the same folder and start the app using '''python WorkingOnIt.py''':
 +
[[Image:Screenshotupdate.jpg]]

Latest revision as of 11:57, 13 August 2017


This PySide tutorial shows you how to use native Python threads (non-QThread, i.e. threading.Thread) to carry out work in the background (e.g. downloading files). In the special case of downloading, you might want to use QNetworkAccessManager and friends, but in this case, we assume that you can't use it for whatever reason (e.g. because you want to use Twisted or because you already have your special download code that you want to reuse).

WorkingOnIt.py

Importing required modules

We will be using standard Python modules for threading (threading) and for downloading (urllib). From PySide, we need the standard module QtCore, QtGui and QtDeclarative:

import os
import sys
import threading
import urllib

from PySide import QtCore, QtGui, QtDeclarative

The Downloader object

We now subclass QObject (so we can have Signals, Slots and Properties in our downloader) and implement all the properties that we need for downloading the file and also for displaying the current status in the UI:

class Downloader(QtCore.QObject):
    def __init__(self, url, filename=None):
        QtCore.QObject.__init__(self)
        self._url = url
        
        if filename is None:
            filename = os.path.basename(self._url)
            
        self._filename = filename
        self._progress = 0.
        self._running = False
        self._size = -1

    def _download(self):
        def reporthook(pos, block, total):
            if self.size != total:
                self._size = total

            self.on_size.emit()
            self.progress = float(pos * block) / float(total)
            urllib.urlretrieve(self._url, self._filename, reporthook)
            self.running = False

    @QtCore.Slot()
    def start_download(self):
        if not self.running:
            self.running = True

        thread = threading.Thread(target=self._download)
        thread.start()

    def _get_progress(self):
        return self._progress

    def _set_progress(self, progress):
        self._progress = progress
        self.on_progress.emit()

    def _get_running(self):
        return self._running

    def _set_running(self, running):
        self._running = running
        self.on_running.emit()

    def _get_filename(self):
        return self._filename

    def _get_size(self):
        return self._size

    on_progress = QtCore.Signal()
    on_running = QtCore.Signal()
    on_filename = QtCore.Signal()
    on_size = QtCore.Signal()

    progress = QtCore.Property(float, _get_progress, _set_progress, notify=on_progress)
    running = QtCore.Property(bool, _get_running, _set_running, notify=on_running)
    filename = QtCore.Property(str, _get_filename, notify=on_filename)
    size = QtCore.Property(int, '', _get_size, notify=on_size)

Creating a new Downloader instance

As an example, we create a new Downloader here that downloads a kernel image for the N900 from the MeeGo repository:

downloader = Downloader
('http://repo.meego.com/MeeGo/builds/trunk/1.1.80.8.20101130.1/handset/images/meego-handset-armv7l-n900/meego-handset-armv7l-
n900-1.1.80.8.20101130.1-vmlinuz-2.6.35.3-13.6-n900')

QApplication, QDeclarativeView and context properties

As usual, we simply instantiate a new QApplication and a QDeclarativeView. Our Downloader is exposed to the QML context by setting it as context property downloader on the rootContext of our view. We then simply load the QML file via setSource, show the view and execute the application:

app = QtGui.QApplication(sys.argv)
view = QtDeclarative.QDeclarativeView()
view.rootContext().setContextProperty('downloader', downloader)
view.setSource(file.replace('.py', '.qml'))
view.show()
app.exec''()

WorkingOnIt.qml

This is the QML UI for our downloader example. The interesting parts here are:

  • When the button is clicked, downloader.start_download() (a PySide Slot) is called, which starts the thread
  • The UI elements use properties of the downloader to determine visiblity and content- they are automatically updated when the properties are notified to be updated
import Qt 4.7

Rectangle {
 width: 200; height: 160

function formatProgress(size, progress) {
 return "" + parseInt(progress*size/1024) +
 " KiB ("''parseInt(progress*100.)'' "%)";
 }

Text {
 x: progressBar.x; y: 20
 width: progressBar.width
 font.pixelSize: 8
 text: downloader.filename
 elide: Text.ElideRight
 }

Rectangle {
 id: progressBar
 color: "#aaa"

x: 20; y: 60
 width: parent.width-40
 height: 20

Rectangle {
 color: downloader.progress<1?"#ee8":"#8e8"
 clip: true

anchors {
 top: parent.top
 bottom: parent.bottom
 left: parent.left
 }

width: parent.width*downloader.progress

Text {
 anchors {
 fill: parent
 rightMargin: 5
 }
 color: "black"
 text: formatProgress(downloader.size, downloader.progress)
 verticalAlignment: Text.AlignVCenter
 horizontalAlignment: Text.AlignRight
 }
 }
 }

Rectangle {
 anchors.left: progressBar.left
 anchors.right: progressBar.right

color: "#aad"
 y: progressBar.y + progressBar.height + 20
 height: 40

Text {
 anchors.fill: parent
 color: "#003"
 text: downloader.running?"Please wait…":"Start download"

verticalAlignment: Text.AlignVCenter
 horizontalAlignment: Text.AlignHCenter
 }

MouseArea {
 anchors.fill: parent
 onClicked: { downloader.start_download() }
 }
 }
}

How the example app looks

Save the files WorkingOnIt.py and WorkingOnIt.qml in the same folder and start the app using python WorkingOnIt.py: Screenshotupdate.jpg