Mapping MapPolyline on the map QML. C++/Qt - c++

Question

On the instructions I should to display map on the screen and draw on it the line. Try to do this:
main.cpp
#include <QGeoPath>
#include <QGuiApplication>
#include <QQmlApplicationEngine>
#include <QQmlContext>
#include <QTimer>
class PathController: public QObject{
Q_OBJECT
Q_PROPERTY(QGeoPath geopath READ geoPath WRITE setGeoPath NOTIFY geopathChanged)
public:
PathController(QObject *parent = 0) : QObject(parent) {}
QGeoPath geoPath() const {
return mGeoPath;
}
void setGeoPath(const QGeoPath &geoPath) {
if(geoPath != mGeoPath) {
mGeoPath = geoPath;
emit geopathChanged();
}
}
signals:
void geopathChanged();
private:
QGeoPath mGeoPath;
};
int main(int argc, char *argv[]) {
QGuiApplication app(argc, argv);
QGeoPath path;
path.addCoordinate(QGeoCoordinate(55.006355, 92.860984));
path.addCoordinate(QGeoCoordinate(55.1, 93));
path.addCoordinate(QGeoCoordinate(56.1, 92.777));
PathController controller;
controller.setGeoPath(path);
QQmlApplicationEngine engine;
engine.rootContext()->setContextProperty("pathController", &controller);
engine.load(QUrl(QStringLiteral("qrc:/main.qml")));
return app.exec();
}
#include "main.moc"
main.qml
import QtLocation 5.6
import QtPositioning 5.6
Window {
visible: true
width: 640
height: 480
Plugin {
id: osmMapPlugin
name: "osm"
}
Map {
anchors.fill: parent
plugin: osmMapPlugin
center: QtPositioning.coordinate(56.006355, 92.860984)
zoomLevel: 10
MapPolyline {
id: pl
line.width: 3
line.color: 'red'
}
}
Connections{
target: pathController
onGeopathChanged: {
var lines = []
for(var i=0; i < pathController.geopath.size(); i++){
lines[i] = pathController.geopath.coordinateAt(i)
}
pl.path = lines
}
}
}
However, get a blank map. The lines do not appear. Question - how to render lines? They do exist, just like "invisible".
Should be a great triangle
And if you call printf("%s" controller.geoPath().toString().toUtf8().constData()); after assignment - you will see exactly what I entered. But the map is empty for some reason. Help, please.

Answer 1

The error is caused because when a new QGeoPath is established through setGeoPath, it issues the signal to update but at that moment the .qml is not started so the connection is not made so onGeopathChanged is not called in qml since after the first change it never changed back.
A possible solution is to use Component.onCompleted so that it notifies next to onGeopathChanged that there is a change as I show in the following code:
import QtQuick 2.9
import QtQuick.Window 2.2
import QtLocation 5.6
import QtPositioning 5.6
Window {
visible: true
width: 640
height: 480
Plugin {
id: osmMapPlugin
name: "osm"
}
Map {
anchors.fill: parent
plugin: osmMapPlugin
center: QtPositioning.coordinate(56.006355, 92.860984)
zoomLevel: 10
MapPolyline {
id: pl
line.width: 10
line.color: 'red'
}
}
function loadPath(){
var lines = []
for(var i=0; i < pathController.geopath.size(); i++){
lines[i] = pathController.geopath.coordinateAt(i)
}
return lines;
}
Connections{
target: pathController
onGeopathChanged: pl.path = loadPath()
}
Component.onCompleted: pl.path = loadPath()
}