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javascriptpythonpyqtpyqt5qtwebchannel

How to pass info from JS to Python using QWebChannel

I have building a GUI in Python through PyQt5. I am showing a web browser with a google maps page. The user is supposed to move the marker and my program should process the coordinates of the marker. Therefore I have to pass the coordinates from JS to Python, but I can't manage to make it work.

Here is the HTML file:

<html>
<head>
<meta name="viewport" content="initial-scale=1.0, user-scalable=yes" />
<script type="text/javascript" src="http://maps.google.com/maps/api/js?sensor=false"></script>
<script type="text/javascript">

 function geocodePosition(pos) {
  geocoder.geocode({
    latLng: pos
  }, function(responses) {
    if (responses && responses.length > 0) {
      updateMarkerAddress(responses[0].formatted_address);
    } else {
      updateMarkerAddress('Cannot determine address at this location.');
    }
  });
}

function updateMarkerStatus(str) {
  document.getElementById('markerStatus').innerHTML = str;
}

function updateMarkerPosition(latLng) {
  document.getElementById('info').innerHTML = [
    latLng.lat(),
    latLng.lng()
  ].join(', ');
}

function updateMarkerAddress(str) {
  document.getElementById('address').innerHTML = str;
}


var geocoder = new google.maps.Geocoder();
var map;


var goldStar = {
    path: 'M 125,5 155,90 245,90 175,145 200,230 125,180 50,230 75,145 5,90 95,90 z',
    fillColor: 'yellow',
    fillOpacity: 0.8,
    scale: 0.1,
    strokeColor: 'gold',
    strokeWeight: 1
};



function addMarker(lat, lon, city, url) {
    var newmarker = new google.maps.Marker({
        position: new google.maps.LatLng(lat, lon),
        icon: goldStar,
        map: map,
        title: city
    });
    newmarker['infowindow'] = new google.maps.InfoWindow({
            content: url
        });
    google.maps.event.addListener(newmarker, 'click', function() {
        this['infowindow'].open(map, this);
    });
}


function initialize() {
  var latLng = new google.maps.LatLng(40.767367, -111.848007);
  // create as a global variable
  map = new google.maps.Map(document.getElementById('mapCanvas'), {
    zoom: 11,
    center: latLng,
    mapTypeId: google.maps.MapTypeId.ROADMAP
  });
    var marker = new google.maps.Marker({
    position: latLng,
    title: 'Point A',
    map: map,
    draggable: true
  });

  // Update current position info.
  updateMarkerPosition(latLng);
  geocodePosition(latLng);

  // Add dragging event listeners.
  google.maps.event.addListener(marker, 'dragstart', function() {
    updateMarkerAddress('Dragging...');
  });

  google.maps.event.addListener(marker, 'drag', function() {
    updateMarkerStatus('Dragging...');
    updateMarkerPosition(marker.getPosition());
  });

  google.maps.event.addListener(marker, 'dragend', function() {
    updateMarkerStatus('Drag ended');
    geocodePosition(marker.getPosition());
  });

//  return latLng
}


// Onload handler to fire off the app.
google.maps.event.addDomListener(window, 'load', initialize);

</script>
</head>
<body>
  <style>
  #mapCanvas {

    # width: 1000px;
    width: 102%;
    height: 500px;
    float: left;
    margin-left: -7px;
    margin-right: -10px;
    margin-top: -7px;
    margin-bottom: 10px;
  }
  #infoPanel {
    float: center;
    margin-left: 20px;
  }
  #infoPanel div {
    margin-bottom: 10px;
  }
  </style>

      <font size="3" color="black" face="verdana">
  <div id="mapCanvas"></div>
  <div id="infoPanel">
    <font size="3" color="black" face="verdana">
    <!-- <b>Marker status:</b> -->
    <div id="markerStatus"><i>Click and drag the marker.</i></div>
    <font size="3" color="black" face="verdana">
    <b>Current position:</b>
    <div id="info"></div>
    <!--<b>Closest matching address:</b>-->
    <!--<div id="address"></div>-->
  </div>
</body>
</html>

And here is the Python code:

import sys
from PyQt5.QtWidgets import *
from GUI_tmy3 import *

class ShowMap_fun(QMainWindow):
    def __init__(self):
        super().__init__()
        self.map_ui = Ui_tmy3page()  # The name of my top level object is MainWindow
        self.map_ui.setupUi(self)
        self.map_ui.html_code.load(QtCore.QUrl.fromLocalFile('/Users/carlo/Dropbox/modules_NEW/useless.html'))


if __name__ == '__main__':
    app = QApplication(sys.argv)
    ex = ShowMap_fun()
    ex.show()
    sys.exit(app.exec_())

With the GUI code:

from PyQt5 import QtCore, QtGui, QtWidgets

class Ui_tmy3page(object):
    def setupUi(self, MainWindow):
        MainWindow.setObjectName("MainWindow")
        MainWindow.resize(900, 620)
        MainWindow.setMinimumSize(QtCore.QSize(900, 620))
        MainWindow.setMaximumSize(QtCore.QSize(900, 620))
        MainWindow.setWindowTitle("")
        self.centralwidget = QtWidgets.QWidget(MainWindow)
        self.centralwidget.setObjectName("centralwidget")
        self.html_code = QtWebEngineWidgets.QWebEngineView(self.centralwidget)
        self.html_code.setGeometry(QtCore.QRect(0, 0, 901, 621))
        self.html_code.setUrl(QtCore.QUrl("about:blank"))
        self.html_code.setObjectName("html_code")
        MainWindow.setCentralWidget(self.centralwidget)

        self.retranslateUi(MainWindow)
        QtCore.QMetaObject.connectSlotsByName(MainWindow)

    def retranslateUi(self, MainWindow):
        pass

from PyQt5 import QtWebEngineWidgets

I understand the easiest method would be to use QWebChannel. I found an example here but I can't adapt it to my case.

Any suggestion?

Solution

  • To make the work more orderly I have separated the javascript code to a new file called useless.js.

    What you should do is create a QWebChannel object, set it on the page and register the object, also you must create a slot that receives the information:

    class ShowMap_fun(QMainWindow):
    def __init__(self):
        super().__init__()
        self.map_ui = Ui_tmy3page()  # The name of my top level object is MainWindow
        self.map_ui.setupUi(self)

        channel = QtWebChannel.QWebChannel(self.map_ui.html_code.page())
        self.map_ui.html_code.page().setWebChannel(channel)
        channel.registerObject("jshelper", self)

        self.map_ui.html_code.load(QtCore.QUrl.fromLocalFile(QtCore.QDir.current().filePath("useless.html")))

    @QtCore.pyqtSlot(float, float)
    def markerMoved(self, lat, lng):
        print(lat, lng)

    Then you must add the qwebchannel.js file to the .html

    useless.html

    <html>
<head>
    <meta name="viewport" content="initial-scale=1.0, user-scalable=yes"/>
    <script type="text/javascript" src="./qwebchannel.js"></script>
    <script type="text/javascript" src="http://maps.google.com/maps/api/js?sensor=false"></script>
    <script type="text/javascript" src="useless.js"></script>
</head>
[...]

    In the code js the object must be obtained:

    useless.js

    var jshelper;

new QWebChannel(qt.webChannelTransport, function (channel) {
    jshelper = channel.objects.jshelper;
});

[...]

google.maps.event.addListener(marker, 'drag', function () {
    updateMarkerStatus('Dragging...');
    updateMarkerPosition(marker.getPosition());
    jshelper.markerMoved(marker.position.lat(), marker.position.lng());
});

    The complete example can be found at the following link