QT 通过 C++ 添加映射 QML 项目

Question

我尝试将 QML 地图项（例如 MapQuickItem 或 MapCircle）从 C++ 添加到我的地图中。不幸的是，他们没有出现在地图上。只需使用 QML 矩形即可使用相同的代码。rect v1 是用于测试其是否有效的矩形。rect v2 是不起作用的mapCircle。当我将圆 QML 代码 1:1 添加到地图 QML 代码中时，它工作正常。

主要.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();
}

直方图.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
        }
}

直方图.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
}

地图.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

确定某个项目是地图的子项并不意味着它显示在地图上，如果您想添加项目，则必须使用该方法，addMapItem()在 C++ 中您可以使用QMetaObject::invokeMethod()该方法来调用该方法，但需要访问QDeclarativeGeoMapItemBase属于私有Qt API的类型，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

主程序

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

前一种方法的问题在于，它很危险，因为地图或任何 QML 元素都可以随时被删除，从而可能产生问题，此外它还限制了 QML 的修改，最后需要访问私有的 Qt API 可能会更改，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，在其中创建项目并将其添加到地图中：

  #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();
  }
  

  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)
              }
          }
      }
  }
  

  或者

  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 一起使用：

  #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
          }
      }
  }