c++ - 为什么我不能从 QML 读取暴露的 C++ 数据？

Question

我制作这个类是为了将它用作数据容器。我从 json 中读取了一些数据(在 C++ 中)并填充了我存储在 dataHandler 的 m_guiAreas 列表中的 GUIArea 列表。在 QML 的某个时刻，我向 dataHandler 请求了一系列 selectedAreas。 DataHandler 填充 QList m_selectedGuiAreas 并发出 selectedAreasChanged() 信号。现在我希望看到一个矩形网格，其中填充了选定的数据，但我什么也没看到。在 C++ 级别，当发出 selectedAreasChanged() 时，m_selectedGuiAreas 结果填充了正确的数据，但在 QML 级别，它似乎是空的，或者数据可能没有正确读取。

这是我用作包装器将数据带到 QML 级别的类:

class GUIArea : public QObject
    {
        Q_OBJECT
        Q_PROPERTY(QString id READ id )
        Q_PROPERTY(QString configurations READ configurations )

        ...

    public:
        explicit GUIArea(QObject *parent = nullptr): QObject (parent) {}

        QString id() {return m_id;}
        void id(QString newId) {m_id = newId;}

        QString configurations() {return m_configuration; }
        void configurations(QString newConfiguration) {m_configuration = newConfiguration;}

        ...

    private:
        QString m_id;
        QString m_configuration;
    };

下面是 dataHandler 类，我在其中声明从 Json 读取的数据列表，并将其从 Qlist 转换为 QQmlPropertyList(我在一些 QML 指南中看到了将 c++ 属性公开给 QML)。initializeDatas 方法读取存储在 m_GUIAreas 中的数据，然后在 m_selectedGUIAreas 中选择要发送到 QML 的数据，最后发出信号 selectedGUIAsChanged()。

class dataHandler : public QObject
    {
        Q_OBJECT
        Q_PROPERTY(QQmlListProperty<GUIArea> selectedGuiAreas READ selectedGuiAreas NOTIFY selectedAreasChanged)

public:
    explicit dataHandler(QObject *parent = nullptr);
    static dataHandler* instance();

    QQmlListProperty<GUIArea> selectedGuiAreas();
    ...

public slots:
        void initializeDatas(const json& blocksList);
    ... 

signals:
    ...
    void selectedAreasChanged();
    ...
private:   
    ... 
    QList<GUIArea *> m_guiAreas;
    QList<GUIArea *> m_selectedGuiAreas;
};

在主文件中，dataHandler 被声明为一个属性:这是代码:

  QQuickView view;
  ...
  view.engine()->rootContext()->setContextProperty("dataHandler", dataHandler::instance());
  ...
  view.show();

下面是我想在 QML 中可视化的页面的一部分。AreaButton 是 Text 中的一个 Rectangle 和属性文本的别名。

Grid {
    id: areasButtonsGrid
    columns: 4
    anchors.fill: parent

    Repeater {
        model: dataHandler.selectedGuiAreas
        delegate:
            AreaButton {
                text: qsTr(model.modelData.programName)
            }
    }
}

Answer 1

代码不完整，无法分析，所以我只提供一个工作代码，以便您分析问题所在:

main.cpp

#include <QGuiApplication>
#include <QQmlContext>
#include <QQuickView>
#include <QTimer>

class GUIArea : public QObject
{
    Q_OBJECT
    Q_PROPERTY(QString id READ id  CONSTANT)
    Q_PROPERTY(QString configurations READ configurations CONSTANT)
public:
    GUIArea(const QString & id="", const QString & configurations="", QObject *parent=nullptr):
        QObject(parent), m_id(id), m_configurations(configurations)
    {}
    QString id() const{return m_id;}
    QString configurations() const{return m_configurations;}
    void setId(const QString &id){
        m_id = id;
    }
    void setConfigurations(const QString &configurations){
        m_configurations = configurations;
    }
private:
    QString m_id;
    QString m_configurations;
};

class DataHandler: public QObject
{
    Q_OBJECT
    Q_PROPERTY(QQmlListProperty<GUIArea> selectedGuiAreas READ selectedGuiAreas NOTIFY selectedAreasChanged)
    using QObject::QObject;
public:
    static DataHandler& instance(){
        static DataHandler handler;
        return handler;
    }
    QQmlListProperty<GUIArea> selectedGuiAreas(){
        return QQmlListProperty<GUIArea>(this, m_selectedGuiAreas);
    }
    void append(GUIArea *area){
        if(area){
            m_selectedGuiAreas << area;
            emit selectedAreasChanged();
        }
    }
signals:
    void selectedAreasChanged();
private:
    QList<GUIArea *> m_selectedGuiAreas;
};

int main(int argc, char *argv[])
{
    QCoreApplication::setAttribute(Qt::AA_EnableHighDpiScaling);
    QGuiApplication app(argc, argv);
    qmlRegisterType<GUIArea>();
    QQuickView view;
    view.rootContext()->setContextProperty("dataHandler", &DataHandler::instance());
    view.setSource(QUrl(QStringLiteral("qrc:/main.qml")));
    view.show();
    QTimer timer;
    static int counter =0;
    QObject::connect(&timer, &QTimer::timeout, [](){
        GUIArea *area = new GUIArea(QString::number(counter),
                                    QString("configuratio-%1").arg(counter),
                                    &DataHandler::instance());
        DataHandler::instance().append(area);
        counter++;
    });
    timer.start(1000);
    return app.exec();
}
#include "main.moc"

ma​​in.qml

import QtQuick 2.12

Grid {
    id: areasButtonsGrid
    columns: 5
    width: 640
    height: 480
    spacing: 20
    Repeater {
        model: dataHandler.selectedGuiAreas
        delegate:
            Rectangle{
            width: 100
            height: 100
            color: "blue"
            Text {
                anchors.fill: parent
                text: qsTr(model.modelData.configurations)
                verticalAlignment: Text.AlignVCenter
                horizontalAlignment: Text.AlignHCenter
            }
        }
    }
}