Qt/QML 如何从<T> QAbstractListModel 的虚拟数据 metod 返回 QList 集合

Question

我想总结一下该怎么做。我有一个DataObject类，其中有成员：

QString first;QString last;QList<SubObject*> m_sublist; 

我正在使用QAbstractListModel。我可以首先和最后引用列表视图，但我不能像m_sublist[0].lesson那样引用。它给了我这样的错误：

无法读取未定义的属性"教训"。

我的代码：Dataobject.h

        class SubObject :public QObject
    {
        Q_OBJECT

    public:
        SubObject(const QString &lesson,QObject *parent = 0);
        const QString lesson;
    private:

    //    bool operator==(const SubObject*  &other) const {
    //           return other->lesson == lesson;
    //    }
    };
    class DataObject :public QObject{
        Q_OBJECT
    public:
    DataObject(const QString &firstName,
                const QString &lastName,
                const QList<SubObject*>   &sublist);

    QString first;
    QString last;
    QList<SubObject*> m_sublist;
    };

simplelistmodel.h

    class SimpleListModel : public QAbstractListModel {
        Q_OBJECT
    public:
        SimpleListModel(QObject *parent=0);
        QVariant data(const QModelIndex &index, int role = Qt::DisplayRole) const;
        int rowCount(const QModelIndex &parent = QModelIndex()) const;
        QHash<int,QByteArray> roleNames() const { return  m_roleNames; }

    private:
    // Q_DISABLE_COPY(SimpleListModel);
        QList<DataObject*> m_items;
        static const int FirstNameRole;
        static const int LastNameRole;
        static const int SubListRole;
    QHash<int, QByteArray> m_roleNames;
    };

简单列表模型.cpp

        const int SimpleListModel::FirstNameRole = Qt::UserRole + 1;
    const int SimpleListModel::LastNameRole = Qt::UserRole + 2;
    const int SimpleListModel::SubListRole = Qt::UserRole + 3;

    SimpleListModel::SimpleListModel(QObject *parent) :
            QAbstractListModel(parent) {
        // Create dummy data for the list
        QList<SubObject*> mysublist;
        mysublist.append(new SubObject("MAT"));
        mysublist.append(new SubObject("FEN"));

        DataObject *first = new DataObject(QString("Arthur"), QString("Dent"),mysublist);
        DataObject *second = new DataObject(QString("Ford"), QString("Prefect"),mysublist);
        DataObject *third = new DataObject(QString("Zaphod"), QString("Beeblebrox"),mysublist);
        m_items.append(first);
        m_items.append(second);
        m_items.append(third);

    // m_roleNames = SimpleListModel::roleNames();
    m_roleNames.insert(FirstNameRole, QByteArray("firstName"));
    m_roleNames.insert(LastNameRole, QByteArray("lastName"));
    m_roleNames.insert(SubListRole, QByteArray("subList"));

    }
    int SimpleListModel::rowCount(const QModelIndex &) const {
    return m_items.size();
    }
    QVariant SimpleListModel::data(const QModelIndex &index,
                                                int role) const {
        if (!index.isValid())
            return QVariant(); // Return Null variant if index is invalid
        if (index.row() > (m_items.size()-1) )
            return QVariant();
        DataObject *dobj = m_items.at(index.row());
        switch (role) {
        case Qt::DisplayRole: // The default display role now displays the first name as well
        case FirstNameRole:
            return QVariant::fromValue(dobj->first);
        case LastNameRole:
            return QVariant::fromValue(dobj->last);
        case SubListRole:
            return QVariant::fromValue(dobj->m_sublist);
        default:
            return QVariant();
        }
    }

主.cpp

        int main(int argc, char *argv[]) {
        QGuiApplication app(argc, argv);
        QQmlApplicationEngine engine;
        SimpleListModel model;

        QQmlContext *classContext = engine.rootContext();
        classContext->setContextProperty("absmodel",&model);
        engine.load(QUrl(QStringLiteral("qrc:/myuiscript.qml")));
        return app.exec(); }

myuiscript.qml

        import QtQuick 2.0
    import QtQuick.Window 2.0
    Window {
        id: bgRect
        width: 200
        height: 200
            color: "black"
            visible: true
            ListView {
                id: myListView
                anchors.fill: parent
                delegate: myDelegate
                model: absmodel
            }
            Component {
    id: myDelegate
            Item {
    width: 200
            height: 40
            Rectangle {
                anchors.fill: parent
                    anchors.margins: 2
                    radius: 5
                    color: "lightsteelblue"
                    Row {
                        anchors.verticalCenter: parent.verticalCenter
                            Text {
    text: firstName
            color: "black"
            font.bold: true
                            }
                        Text {
    text: subList[0].lesson
            color: "black"
                        }
                    }
            }
            }
            }

    }

我找不到任何解决方案。虚拟数据模型返回单一类型的对象。 FirsName是一个字符串。我不能像firstName(rolename)那样引用列表视图代表.LastName也像lastName(rolename)一样被引用。但我不能像sublist[0].lesson那样指代subList(roleNames).

我的目标很简单。我想通过使用角色名将单个类型(int,QString ....)引用到委托中的文本。我无法使用rolename(subList[0].lesson)将集合type(QList<SubObject*>)引用到委托中的文本。如何获得它们？

Answer 1

让我们一步一步地修复它。QML 中的此行text: subList[0].lesson生成错误消息

类型错误： 无法读取未定义的属性"教训"

这意味着subList[0]是一个未定义的对象，QML 引擎无法从该对象读取任何属性，包括lesson。事实上，从模型返回的subList是一个定义良好的QList<SubObject*>对象，但不是subList[0] QList<SubObject*>因为它不是 QML 列表。要将列表从 C++ 正确传递到 QML，请返回 QVariantList 而不是 QList 。

//class DataObject
DataObject(const QString &firstName,
            const QString &lastName,
            const QVariantList &sublist);
QVariantList    m_sublist; //use QVariantList instead of QList<SubObject*>
//---
//SimpleListModel::SimpleListModel
QVariantList mysublist; //use QVariantList instead of QList<SubObject*>
mysublist.append(QVariant::fromValue(new SubObject("MAT", this))); //remember parent
mysublist.append(QVariant::fromValue(new SubObject("FEN", this)));
//...

现在，可以在 QML 中访问subList[0]，但不能subList[0].lesson 。若要访问 C++ 类中的属性，请使用Q_PROPERTY宏显式定义该属性。

class SubObject :public QObject
{
    Q_OBJECT
    Q_PROPERTY(QString lesson READ getLesson NOTIFY lessonChanged)
public:
    SubObject(const QString &lesson,QObject *parent = 0):
        QObject(parent), m_lesson(lesson){;}
    QString getLesson() const {return m_lesson;}
signals:
    void lessonChanged();
private:
    QString m_lesson;
};

QML代码现在可以工作了。