无法从QML向C++传递数据，Qt 5.15.2报错求助

运行错误信息 #

QObject::connect(QQuickWindow, QDeclarativeGeoMap): invalid nullptr parameter
QObject::connect(QQuickWindow, QDeclarativeGeoMap): invalid nullptr parameter
QGeoTileProviderOsm: Tileserver disabled at QUrl("http://maps-redirect.qt.io/osm/5.8/satellite")
QGeoTileFetcherOsm: all providers resolved
QGeoTileProviderOsm: Tileserver disabled at QUrl("http://maps-redirect.qt.io/osm/5.8/satellite")
QGeoTileFetcherOsm: all providers resolved

环境信息 #

使用Qt版本：5.15.2

相关代码 #

QML部分代码 #

import QtQuick 2.15
import QtQuick.Controls 2.15
import QtLocation 5.15
import QtPositioning 5.15
import QtQuick.Dialogs 1.3

Rectangle {
    id: telecom
    width: 800
    height: 600

    signal setRect(double x, double y, double width, double height)

    Plugin {
        id: mapPlugin
        name: "osm"

    }

    Map {
        id: map
        anchors.fill: parent
        plugin: mapPlugin
        center: QtPositioning.coordinate(55.7558, 37.6173)
        zoomLevel: 10

        MouseArea {
            id: mapMouseArea
            anchors.fill: parent
            onPressed: {
                mapMouseArea.active = true
            }
            onReleased: {
                mapMouseArea.active = false
            }
        }
    }

    Rectangle {
        id: rect
        width: 0
        height: 0
        color: "blue"
        opacity: 0.5
        border.color: "black"
        border.width: 2
        visible: false

        x: 100
        y: 100
    }

    MouseArea {
        id: mouseArea
        anchors.fill: parent
        onPressed: {
            rect.x = mouseArea.mouseX
            rect.y = mouseArea.mouseY
            rect.width = 0
            rect.height = 0
            rect.visible = true
        }

        onReleased: {
            rect.width = Math.abs(mouseArea.mouseX - rect.x)
            rect.height = Math.abs(mouseArea.mouseY - rect.y)
            setRect(rect.x, rect.y, rect.width, rect.height)
        }
...

main.cpp代码 #

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    QQmlApplicationEngine engine;

    RectangleHandler rectangleHandler;
    engine.rootContext()->setContextProperty("rectangleHandler", &rectangleHandler);

    const QUrl url(QStringLiteral("qrc:/places_map.qml"));
    QObject::connect(&engine, &QQmlApplicationEngine::objectCreated,
                     &a, [url](QObject *obj, const QUrl &objUrl) {
                         if (!obj && url == objUrl) {
                             qCritical() << "Error 1";
                             QCoreApplication::exit(-1);
                         }
                     }, Qt::QueuedConnection);

    engine.load(url);
    if (engine.rootObjects().isEmpty()) {
        qCritical() << "Error 2";
        return -1;
    }

    MainWindow w;
    w.show();
    return a.exec();
}

核心需求 #

需将QML中绘制的矩形坐标数据传递至C++做后续处理，但运行时触发上述错误，求解决方法。

解决方案 #

1. 修复invalid nullptr parameter连接错误 #

代码中同时使用QQmlApplicationEngine加载QML和MainWindow，导致QML的Map控件无法找到对应QQuickWindow，触发空指针连接错误。

• 修复方式：二选一使用QML窗口或Qt Widgets窗口。若要保留QML的Map控件，需移除MainWindow相关代码，并将QML根元素改为ApplicationWindow：
  • 修改后的main.cpp：

    int main(int argc, char *argv[])
    {
        QApplication a(argc, argv);
        QQmlApplicationEngine engine;
    
        RectangleHandler rectangleHandler;
        engine.rootContext()->setContextProperty("rectangleHandler", &rectangleHandler);
    
        const QUrl url(QStringLiteral("qrc:/places_map.qml"));
        QObject::connect(&engine, &QQmlApplicationEngine::objectCreated,
                         &a, [url](QObject *obj, const QUrl &objUrl) {
                             if (!obj && url == objUrl) {
                                 qCritical() << "Error 1";
                                 QCoreApplication::exit(-1);
                             }
                         }, Qt::QueuedConnection);
    
        engine.load(url);
        if (engine.rootObjects().isEmpty()) {
            qCritical() << "Error 2";
            return -1;
        }
    
        return a.exec();
    }
    

  • 修改QML根元素：

    import QtQuick.Window 2.15
    
    ApplicationWindow {
        id: telecom
        width: 800
        height: 600
        visible: true
    
        // 原Rectangle内的所有内容移至此处
        signal setRect(double x, double y, double width, double height)
    
        Plugin {
            id: mapPlugin
            name: "osm"
        }
    
        // ... 其余代码保持不变
    }
    

2. 实现QML信号到C++的传递 #

当前QML定义了setRect信号，但未连接到C++的rectangleHandler对象，需补充连接逻辑：

• 在QML中添加信号连接：

  Component.onCompleted: {
      telecom.setRect.connect(rectangleHandler.onSetRect)
  }
  

• 确保RectangleHandler类继承QObject并定义对应槽函数：

  #include <QObject>
  
  class RectangleHandler : public QObject
  {
      Q_OBJECT
  public slots:
      void onSetRect(double x, double y, double width, double height) {
          // 在此处理传递过来的矩形数据
      }
  };
  

3. 修复地图瓦片服务禁用问题 #

Qt 5.15.2默认的OSM卫星瓦片地址已失效，需手动指定可用的瓦片源：

Plugin {
    id: mapPlugin
    name: "osm"
    PluginParameter {
        name: "osm.mapping.providersrepository.disabled"
        value: true
    }
    PluginParameter {
        name: "osm.mapping.providers.order"
        value: "custom"
    }
    PluginParameter {
        name: "osm.mapping.provider.custom.type"
        value: "xyz"
    }
    PluginParameter {
        name: "osm.mapping.provider.custom.url"
        value: "https://tile.openstreetmap.org/{z}/{x}/{y}.png"
    }
    PluginParameter {
        name: "osm.mapping.provider.custom.zenith"
        value: 0
    }
    PluginParameter {
        name: "osm.mapping.provider.custom.azimuth"
        value: 0
    }
}

内容的提问来源于stack exchange，提问作者3614n