QT QmlMap PolyLine not updated properly when underlying model changes - c++

Question

I'm trying to connect several GeoCoordinates with a polyline in my map. The Coordinates are stored in an model (QAbstractListModel) class, where I can modify (remove and add) the Coords in C++.
Simply displaying markers for every coordinate works fine, but when I connect them with a Polyline and delete some existing coordinates from my model, the Polyline does not get updated.
map.qml
import QtQuick 2.0
import QtLocation 5.6
import QtPositioning 5.6
Item {
width: 512
height: 512
visible: true
id: mainWindow
Map { //our map
anchors.fill: parent
id: map
plugin: mapPlugin
zoomLevel: 14
focus: true
Plugin {
id: mapPlugin
name: "osm"
}
MapItemView {
model: markerModel
delegate: mapcomponent
}
MapItemView {
model: markerModel
delegate: MapPolyline {
antialiasing: true
line.color: "darkBlue"
line.width: 3
path: pathRole
}
}
Component {
id: mapcomponent
MapQuickItem{
id: marker
coordinate: positionRole
sourceItem: Image{
id: markerimage
width: 20
height: 30
source: "qrc:/marker.png"
}
anchorPoint.x: markerimage.width / 2
anchorPoint.y: markerimage.height
}
}
MouseArea {
anchors.fill: parent
onClicked: {
var coord = parent.toCoordinate(Qt.point(mouse.x,mouse.y))
markerModel.addMarker(coord)
}
}
}
}
markermodel.h which stores the coordinates
class MarkerModel : public QAbstractListModel {
Q_OBJECT
public:
using QAbstractListModel::QAbstractListModel;
enum MarkerRoles{positionRole = Qt::UserRole, pathRole};
Q_INVOKABLE void addMarker(const QGeoCoordinate &coordinate) {
beginInsertRows(QModelIndex(), rowCount(), rowCount());
m_coordinates.append(coordinate);
endInsertRows();
}
int rowCount(const QModelIndex &parent = QModelIndex()) const override {
Q_UNUSED(parent)
return m_coordinates.count();
}
bool removeRows(int row, int count, const QModelIndex &parent = QModelIndex()) override {
if(row + count > m_coordinates.count() || row < 0)
return false;
beginRemoveRows(parent, row, row+count-1);
for(int i = 0; i < count; ++i)
m_coordinates.removeAt(row + i);
endRemoveRows();
return true;
}
bool removeRow(int row, const QModelIndex &parent = QModelIndex()) {
return removeRows(row, 1, parent);
}
QVariant data(const QModelIndex &index, int role = Qt::DisplayRole) const override {
if (index.row() < 0 || index.row() >= m_coordinates.count())
return QVariant();
if(role == Qt::DisplayRole)
return QVariant::fromValue(index.row());
if(role == MarkerModel::positionRole)
return QVariant::fromValue(m_coordinates[index.row()]);
if(role == MarkerModel::pathRole) {
QVariantList coordlist;
for(auto &geocoord : m_coordinates)
coordlist << QVariant::fromValue(geocoord);
return coordlist;
}
return QVariant();
}
QHash<int, QByteArray> roleNames() const {
QHash<int, QByteArray> roles;
roles[positionRole] = "positionRole";
roles[pathRole] = "pathRole";
return roles;
}
private:
QList<QGeoCoordinate> m_coordinates;
};
A gif showing my problem:
Did I miss something when deleting rows in my model? Is there a way to force qml to render the polyline with completly new data from the model?

Answer 1

Having a pathRole doesn't make much sense here. This role is the same for all the rows of your model.
You display n MapPolyline where n is the number of coordinates, you only need one for your entire model.
I would advise you to remove the pathRole and just expose a path property in your model, and emit its notify signal in addMarker and removeRows.

Answer 2

As they indicate your code has a logic error, in my answer I will show the implementation since #GrecKo already explained the correct logic:
markermodel.h
#ifndef MARKERMODEL_H
#define MARKERMODEL_H
#include <QAbstractListModel>
#include <QGeoCoordinate>
class MarkerModel : public QAbstractListModel {
Q_OBJECT
Q_PROPERTY(QVariantList path READ path NOTIFY pathChanged)
public:
enum MarkerRoles{positionRole = Qt::UserRole, pathRole};
MarkerModel(QObject *parent=nullptr): QAbstractListModel(parent)
{
connect(this, &QAbstractListModel::rowsInserted, this, &MarkerModel::pathChanged);
connect(this, &QAbstractListModel::rowsRemoved, this, &MarkerModel::pathChanged);
connect(this, &QAbstractListModel::dataChanged, this, &MarkerModel::pathChanged);
connect(this, &QAbstractListModel::modelReset, this, &MarkerModel::pathChanged);
connect(this, &QAbstractListModel::rowsMoved, this, &MarkerModel::pathChanged);
}
Q_INVOKABLE void addMarker(const QGeoCoordinate &coordinate) {
beginInsertRows(QModelIndex(), rowCount(), rowCount());
m_coordinates.append(coordinate);
endInsertRows();
}
int rowCount(const QModelIndex &parent = QModelIndex()) const override {
if(parent.isValid()) return 0;
return m_coordinates.count();
}
bool removeRows(int row, int count, const QModelIndex &parent = QModelIndex()) override {
if(row + count > m_coordinates.count() || row < 0)
return false;
beginRemoveRows(parent, row, row+count-1);
for(int i = 0; i < count; ++i)
m_coordinates.removeAt(row + i);
endRemoveRows();
return true;
}
bool removeRow(int row, const QModelIndex &parent = QModelIndex()) {
return removeRows(row, 1, parent);
}
QVariant data(const QModelIndex &index, int role = Qt::DisplayRole) const override {
if (index.row() < 0 || index.row() >= m_coordinates.count())
return QVariant();
if(role == Qt::DisplayRole)
return QVariant::fromValue(index.row());
else if(role == MarkerModel::positionRole)
return QVariant::fromValue(m_coordinates[index.row()]);
return QVariant();
}
QHash<int, QByteArray> roleNames() const override{
QHash<int, QByteArray> roles;
roles[positionRole] = "positionRole";
return roles;
}
QVariantList path() const{
QVariantList path;
for(const QGeoCoordinate & coord: m_coordinates){
path << QVariant::fromValue(coord);
}
return path;
}
signals:
void pathChanged();
private:
QList<QGeoCoordinate> m_coordinates;
};
#endif // MARKERMODEL_H
*.qml
import QtQuick 2.0
import QtLocation 5.6
import QtPositioning 5.6
Item {
width: 512
height: 512
visible: true
id: mainWindow
Map { //our map
anchors.fill: parent
id: map
plugin: mapPlugin
zoomLevel: 14
focus: true
Plugin {
id: mapPlugin
name: "osm"
}
MapItemView {
model: markerModel
delegate: mapcomponent
}
MapPolyline{
antialiasing: true
line.color: "darkBlue"
line.width: 3
path: markerModel.path
}
Component {
id: mapcomponent
MapQuickItem{
id: marker
coordinate: positionRole
sourceItem: Image{
id: markerimage
width: 20
height: 30
source: "qrc:/marker.png"
}
anchorPoint.x: markerimage.width / 2
anchorPoint.y: markerimage.height
}
}
MouseArea {
anchors.fill: parent
onClicked: {
var coord = parent.toCoordinate(Qt.point(mouse.x,mouse.y))
markerModel.addMarker(coord)
}
}
}
}