从QAbstractListModel中删除行

Question

我有一个自定义模型，它从QAbstractListModel派生，这是公开给QML。我需要支持添加新项目和删除现有项目的操作。虽然插入操作没有任何问题，但删除操作会导致应用程序在调用endRemoveRows()函数时崩溃。

    void GPageModel::addNewPage()
    {
        if(m_pageList.count()<9)
        {
            beginInsertRows(QModelIndex(),rowCount(),rowCount());
            GPage * page = new GPage();
            QQmlEngine::setObjectOwnership(page,QQmlEngine::CppOwnership);
            page->setParent(this);
            page->setNumber(m_pageList.count());
            page->setName("Page " + QString::number(m_pageList.count()+1));
            m_pageList.append(page);
            endInsertRows();
        }
    }

    void GPageModel::removePage(const int index)
    {
        if(index>=0 && index<m_pageList.count())
        {        
            beginRemoveRows(QModelIndex(),index,index);
            qDebug()<<QString("beginRemoveRows(QModelIndex(),%1,%1)").arg(index);
            GPage * page = m_pageList.at(index);        
            m_pageList.removeAt(index);
            delete page;
            endRemoveRows();
        }
    }

类GPage派生自QObject。在尝试调用endRemoveRows()时，我试图找出是什么导致应用程序崩溃。当endRemoveRows()为called.How时，我得到"ASSERT failure in QList::at："index of of range“，我要从QAbstracListModel中删除行吗？还有别的办法吗？

我在Windows 7 64位计算机上使用Qt 5.1.0。

Answer 1

下面的代码对我来说很好用。你的问题可能出在别的地方。这是针对Qt 5的，因为使用了Qt Quick Controls。

有两个视图访问同一个模型，这在视觉上确认了模型发出了适当的信号来通知视图更改。页面的添加和删除是通过通过Q_INVOKABLE导出的标准insertRows和removeRows方法完成的。到目前为止，这个模型上不需要任何自定义方法。对于QML和QAbstractItemModel之间的接口，Q_INVOKABLE是一些缺失功能的变通方法。

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main.cpp

#include <QGuiApplication>
#include <QQmlApplicationEngine>
#include <QQuickWindow>
#include <QAbstractListModel>
#include <QQmlContext>
#include <QtQml>

class GPage : public QObject {
    Q_OBJECT
    Q_PROPERTY(QString name NOTIFY nameChanged MEMBER m_name)
    Q_PROPERTY(int number NOTIFY numberChanged MEMBER m_number)
    QString m_name;
    int m_number;
public:
    GPage(QObject * parent = 0) : QObject(parent), m_number(0) {}
    GPage(QString name, int number, QObject * parent = 0) :
        QObject(parent), m_name(name), m_number(number) {}
    Q_SIGNAL void nameChanged(const QString &);
    Q_SIGNAL void numberChanged(int);
};

class PageModel : public QAbstractListModel {
    Q_OBJECT
    QList<GPage*> m_pageList;
public:
    PageModel(QObject * parent = 0) : QAbstractListModel(parent) {}
    ~PageModel() { qDeleteAll(m_pageList); }
    int rowCount(const QModelIndex &) const Q_DECL_OVERRIDE {
        return m_pageList.count();
    }
    QVariant data(const QModelIndex &index, int role) const Q_DECL_OVERRIDE {
        if (role == Qt::DisplayRole || role == Qt::EditRole) {
            return QVariant::fromValue<QObject*>(m_pageList.at(index.row()));
        }
        return QVariant();
    }
    bool setData(const QModelIndex &index, const QVariant &value, int role) Q_DECL_OVERRIDE {
        Q_UNUSED(role);
        GPage* page = value.value<GPage*>();
        if (!page) return false;
        if (page == m_pageList.at(index.row())) return true;
        delete m_pageList.at(index.row());
        m_pageList[index.row()] = page;
        QVector<int> roles;
        roles << role;
        emit dataChanged(index, index, roles);
        return true;
    }
    Q_INVOKABLE bool insertRows(int row, int count, const QModelIndex &parent = QModelIndex()) Q_DECL_OVERRIDE {
        Q_UNUSED(parent);
        beginInsertRows(QModelIndex(), row, row + count - 1);
        for (int i = row; i < row + count; ++ i) {
            QString const name = QString("Page %1").arg(i + 1);
            GPage * page = new GPage(name, i + 1, this);
            m_pageList.insert(i, page);
            QQmlEngine::setObjectOwnership(page, QQmlEngine::CppOwnership);
        }
        endInsertRows();
        return true;
    }
    Q_INVOKABLE bool removeRows(int row, int count, const QModelIndex &parent = QModelIndex()) Q_DECL_OVERRIDE {
        Q_UNUSED(parent);
        beginRemoveRows(QModelIndex(), row, row + count - 1);
        while (count--) delete m_pageList.takeAt(row);
        endRemoveRows();
        return true;
    }
};

int main(int argc, char *argv[])
{
    PageModel model1;
    QGuiApplication app(argc, argv);
    QQmlApplicationEngine engine;
    model1.insertRows(0, 1);
    engine.rootContext()->setContextProperty("model1", &model1);
    qmlRegisterType<GPage>();
    engine.load(QUrl("qrc:/main.qml"));
    QObject *topLevel = engine.rootObjects().value(0);
    QQuickWindow *window = qobject_cast<QQuickWindow *>(topLevel);
    window->show();
    return app.exec();
}

#include "main.moc"

main.qml

import QtQuick 2.0
import QtQml.Models 2.1
import QtQuick.Controls 1.0

ApplicationWindow {
    width: 300; height: 300
    Row {
        width: parent.width
        anchors.top: parent.top
        anchors.bottom: column.top
        Component {
            id: commonDelegate
            Rectangle {
                width: view.width
                implicitHeight: editor.implicitHeight + 10
                color: "transparent"
                border.color: "red"
                border.width: 2
                radius: 5
                TextInput {
                    id: editor
                    anchors.margins: 1.5 * parent.border.width
                    anchors.fill: parent
                    text: edit.name // "edit" role of the model, to break the binding loop
                    onTextChanged: {
                        display.name = text;
                        model.display = display
                    }
                }
            }
        }
        ListView {
            id: view
            width: parent.width / 2
            height: parent.height
            model: DelegateModel {
                id: delegateModel1
                model: model1
                delegate: commonDelegate
            }
            spacing: 2
        }
        ListView {
            width: parent.width / 2
            height: parent.height
            model: DelegateModel {
                model: model1
                delegate: commonDelegate
            }
            spacing: 2
        }
    }
    Column {
        id: column;
        anchors.bottom: parent.bottom
        Row {
            Button {
                text: "Add Page";
                onClicked: model1.insertRows(delegateModel1.count, 1)
            }
            Button {
                text: "Remove Page";
                onClicked: model1.removeRows(pageNo.value - 1, 1)
            }
            SpinBox {
                id: pageNo
                minimumValue: 1
                maximumValue: delegateModel1.count;
            }
        }
    }
}

main.qrc

<RCC>
    <qresource prefix="/">
        <file>main.qml</file>
    </qresource>
</RCC>