c++ - 阅读 QML 中结构的 C++ QVector

Question

在我的 C++ 课上我有

struct trackPoint {
  QString lat;
  QString lon;
  QString elevation;
};

  QVector<trackPoint> trackPoints;

在 QML 中，我想将其作为经纬度对的多维数组进行访问

[[0,1],[1,1],[2,1]]

这可以使用 Q_Property 机制吗？因为我很确定结构不能暴露给 QML？

我打平了:-

 Q_PROPERTY(QVector<trackPoint> trackPoints READ gpx)

用一个方法:-

QVector<trackPoint> GPXFileIO::gpx() const {
 return trackPoints;
}

但这给了我错误:-

QMetaProperty::read: Unable to handle unregistered datatype 'QVector<trackPoint>' for property 'GPXFileIO::trackPoints'

Answer 1

将结构暴露给 QML 的一种简单方法是使用 Q_GADGET 和 Q_PROPERTY，这样我们就可以获得结构的每个元素，它们不会成为数组的一部分。另一方面，QVector 支持 QString、int、QUrl 等元素，但不支持新类型，在这种情况下，应该使用 QVariantList。

main.cpp

#include <QGuiApplication>
#include <QQmlApplicationEngine>
#include <QQmlContext>
#include <QVector>

struct TrackPoint {
    Q_GADGET
    Q_PROPERTY(qreal lat MEMBER lat)
    Q_PROPERTY(qreal lon MEMBER lon)
    Q_PROPERTY(qreal elevation MEMBER elevation)
public:
    qreal lat;
    qreal lon;
    qreal elevation;
};

class TrackClass: public QObject
{
    Q_OBJECT
    Q_PROPERTY(QVariantList trackpoints READ gpx)
public:
    TrackClass(QObject *parent=nullptr):QObject(parent){
        trackPoints << TrackPoint{10, 10, 10} << TrackPoint{11, 11, 11};
    }
    QVariantList gpx() const{
        QVariantList l;
        for(const TrackPoint & p: trackPoints){
            l << QVariant::fromValue(p);
        }
        return  l;
    }
private:
    QVector<TrackPoint> trackPoints;
};

int main(int argc, char *argv[])
{
    QCoreApplication::setAttribute(Qt::AA_EnableHighDpiScaling);
    QGuiApplication app(argc, argv);
    TrackClass track;
    QQmlApplicationEngine engine;
    engine.rootContext()->setContextProperty("track", &track);
    engine.load(QUrl(QStringLiteral("qrc:/main.qml")));
    if (engine.rootObjects().isEmpty())
        return -1;
    return app.exec();
}

#include "main.moc"

ma​​in.qml

import QtQuick 2.9
import QtQuick.Window 2.2

Window {
    visible: true
    width: 640
    height: 480
    title: qsTr("Hello World")
    Component.onCompleted: {
        for( var i in track.trackpoints){
            var p = track.trackpoints[i];
            console.log("lat: ", p.lat, "lon: ", p.lon, "elevation: ", p.elevation)
        }
    }
}

输出:

qml: lat:  10 lon:  10 elevation:  10
qml: lat:  11 lon:  11 elevation:  11