c++ - QT通过C++添加Map QML Items

Question

我尝试从 C++ 向我的 map 添加 QML map 项，例如 MapQuickItem 或 MapCircle。不幸的是，它们没有显示在 map 上。只需一个 QML 矩形的相同代码就可以工作。rect v1 是用于测试的矩形。 rect v2 是不起作用的 mapCircle。当我将我的圈子 QML 代码 1:1 添加到我的 map QML 代码中时，它工作正常。

ma​​in.cpp:

int main(int argc, char *argv[])
{
    QGuiApplication app(argc, argv);

    QQuickView *view = new QQuickView;
    view->setSource(QUrl("qrc:/map.qml"));

    QQmlComponent compRect (view->engine(), QUrl("qrc:/rect.qml"));

    view->setWidth(1000);
    view->setHeight(650);
    view->setTitle("GUI");


    QQuickItem *map = view->findChild<QQuickItem*>("map1");

    QQuickItem *rect = qobject_cast<QQuickItem*>(compRect.create(view->rootContext()));

    rect->setParentItem(map);
    rect->setParent(map); //know this is not for visual objects, just for test

    view->show();
    return app.exec();
}

rect.qml v1

import QtQuick 2.14
import QtLocation 5.14
import QtPositioning 5.14

Rectangle
{
        color: "grey"
        opacity: .8

        width: 100
        height: 100
        radius: 4
        Text
        {
            id: text
            anchors.centerIn: parent
            text: "hi"
            color: "orangered"
            font.weight: Font.Bold
        }
}

rect.qml v2

import QtQuick 2.14
import QtLocation 5.14
import QtPositioning 5.14

MapCircle 
{
    center 
    {
        latitude: 47.5
        longitude: 8.9
    }
    radius: 5000.0
    color: 'green'
    border.width: 3
}

ma​​p.qml

import QtQuick 2.12
import QtQuick.Window 2.12
import QtPositioning 5.14
import QtLocation 5.14

Map
{
    objectName: "map1"
    id: map_map
    anchors.centerIn: parent;
    anchors.fill: parent
    plugin: Plugin
    {
        name: "mapboxgl" // "osm", "esri", ...
    }
    center: QtPositioning.coordinate(47.6,9.5)
    zoomLevel: 8

    // get position of device and set map center to it
    PositionSource
    {
        active: true
        onPositionChanged:
        {
            map.center(position.coordinate)
            console.log(position.coordinate)
        }
    }

    Timer
    {
        id: timerReload
        interval: 1000
        repeat: true
        running: true

        onTriggered:
        {
            controller.triggerReload();
        }
    }
}

Answer 1

确定一个项目是 map 的子项并不意味着它显示在 map 上，如果你想添加一个项目你必须使用 addMapItem()方法，在 C++ 中你可以使用 QMetaObject::invokeMethod()调用该方法，但您需要访问属于私有(private) Qt API 的类型 QDeclarativeGeoMapItemBase，考虑到上述解决方案是:

*.pro

QT += quick location location-private
CONFIG += c++11
DEFINES += QT_DEPRECATED_WARNINGS
SOURCES += main.cpp
RESOURCES += qml.qrc

main.cpp

#include <QGuiApplication>
#include <QQuickItem>
#include <QQuickView>

#include <QtLocation/private/qdeclarativegeomapitembase_p.h>

int main(int argc, char *argv[]){
    QCoreApplication::setAttribute(Qt::AA_EnableHighDpiScaling);
    QGuiApplication app(argc, argv);
    QQuickView view;
    view.setSource(QUrl("qrc:/map.qml"));
    view.resize(1000, 650);
    view.setTitle("GUI");
    view.show();
    if(QQuickItem *map = view.findChild<QQuickItem*>("map1")){
        QQmlComponent component(view.engine(), QUrl("qrc:/rect.qml"));
        if(QDeclarativeGeoMapItemBase *rect = qobject_cast<QDeclarativeGeoMapItemBase*>(component.create(view.rootContext()))){
            bool status = QMetaObject::invokeMethod(map,
                                      "addMapItem",
                                      Qt::DirectConnection,
                                      Q_ARG(QDeclarativeGeoMapItemBase*, rect));
            Q_ASSERT(status);
        }
    }
    return app.exec();
}

---

前面的方法的问题是很危险，因为 map 或任何QML元素随时都可能被移除，这样就可能产生问题，而且它限制了QML的修改，最后需要访问私有(private) Qt API 可以更改，恕不另行通知。因此我会提供更好的选择:

• 使用 QObject 并将其导出到 QML，在 QML 中创建项目并将其添加到 map :

  #include <QGuiApplication>
  #include <QQuickView>
  #include <QGeoCoordinate>
  #include <QQmlContext>
  
  class Helper: public QObject{
      Q_OBJECT
  public:
      void addCircle(const QGeoCoordinate & coordinate){
          Q_EMIT circleSignal(coordinate);
      }
  Q_SIGNALS:
      void circleSignal(const QGeoCoordinate & coordinate);
  };
  
  int main(int argc, char *argv[]){
      QCoreApplication::setAttribute(Qt::AA_EnableHighDpiScaling);
      QGuiApplication app(argc, argv);
      QQuickView view;
      Helper helper;
      view.rootContext()->setContextProperty("helper", &helper);
      view.setSource(QUrl("qrc:/map.qml"));
      view.resize(1000, 650);
      view.setTitle("GUI");
      view.show();
      helper.addCircle(QGeoCoordinate(47.6, 9.5));
      return app.exec();
  }
  
  #include "main.moc"
  

  import QtQuick 2.14
  import QtPositioning 5.14
  import QtLocation 5.14
  
  Map{
      id: map_map
      anchors.centerIn: parent;
      anchors.fill: parent
      plugin: Plugin {
          name: "mapboxgl" // "osm", "esri", ...
      }
      center: QtPositioning.coordinate(47.6,9.5)
      zoomLevel: 8
      Connections{
          target: helper
          onCircleSignal: {
              var component = Qt.createComponent("rect.qml");
              if (component.status === Component.Ready){
                  var o = component.createObject(map_map);
                  o.center = coordinate
                  map_map.addMapItem(o)
              }
          }
      }
  }
  

  或

  import QtQuick 2.14
  import QtPositioning 5.14
  import QtLocation 5.14
  
  Map{
      id: map_map
      anchors.centerIn: parent;
      anchors.fill: parent
      plugin: Plugin {
          name: "mapboxgl" // "osm", "esri", ...
      }
      center: QtPositioning.coordinate(47.6,9.5)
      zoomLevel: 8
  
      Component{
          id: provider
          MapCircle{
              center{
                  latitude: 47.6
                  longitude: 9.5
              }
              radius: 5000.0
              color: 'green'
              border.width: 3
          }
      }
      function createCirle(map, position){
          var o  = provider.createObject(map)
          o.center = position
          map.addMapItem(o)
          return o
      }
  
      Connections{
          target: helper
          onCircleSignal: {
              var o = createCirle(map_map, coordinate)
          }
      }
  }
  

• 将模型与 MapItemView 结合使用:

  #include <QGuiApplication>
  #include <QQuickView>
  #include <QGeoCoordinate>
  #include <QQmlContext>
  #include <QStandardItemModel>
  
  int CoordinateRole = Qt::UserRole + 1000;
  
  int main(int argc, char *argv[]){
      QCoreApplication::setAttribute(Qt::AA_EnableHighDpiScaling);
      QGuiApplication app(argc, argv);
      QQuickView view;
      QStandardItemModel model;
      QHash<int, QByteArray> roles;
      roles[CoordinateRole] = QByteArray("coordinate");
      model.setItemRoleNames(roles);
      view.rootContext()->setContextProperty("circle_model", &model);
      view.setSource(QUrl("qrc:/map.qml"));
      view.resize(1000, 650);
      view.setTitle("GUI");
      view.show();
  
      QStandardItem *item = new QStandardItem;
      item->setData(QVariant::fromValue(QGeoCoordinate(47.6, 9.5)), CoordinateRole);
      model.appendRow(item);
  
      return app.exec();
  }
  

  import QtQuick 2.14
  import QtPositioning 5.14
  import QtLocation 5.14
  
  Map{
      id: map_map
      anchors.centerIn: parent;
      anchors.fill: parent
      plugin: Plugin {
          name: "mapboxgl" // "osm", "esri", ...
      }
      center: QtPositioning.coordinate(47.6,9.5)
      zoomLevel: 8
  
      MapItemView{
          model: circle_model
          delegate: MapCircle{
              center: model.coordinate
              radius: 5000.0
              color: 'green'
              border.width: 3
          }
      }
  }