QML List is not updated by QAbstractListModel

[Krulle]

Hello Guys,
I am a bit frustrated because I don't see the problem in this code.
Currently there is a problem with the ListView and the visible of the elements in the list.
I am following this tutorial and trying to get a c++ model to run in QML.

The Problem:
With the C++ model, the ListView is not updated when a new element is added. However, if I use the QML model, it works wonderfully.
If I put the cpp model into a minimal example (as seen at the end), it works.
Does anyone see the problem? I suspect it must be in the QML part.

Thanks a lot.

main.cpp

#include "app_environment.h"
#include "models/functionitem.h"
#include "models/functionmodel.h"
#include "membermodel.h"

#include "memberlist.h"
#include "membermodel.h"

Q_IMPORT_QML_PLUGIN(UtilsPlugin)
Q_IMPORT_QML_PLUGIN(BackendPlugin)

int main(int argc, char *argv[])
{
    set_qt_environment();

    QGuiApplication app(argc, argv);

    qmlRegisterUncreatableType<FunctionItem>("Models", 1, 0, "FunctionItem", QStringLiteral("Only Interface. Cannot create in QML"));
    qmlRegisterUncreatableType<FunctionModel>("Models", 1, 0, "FunctionModel", QStringLiteral("Only Interface. Cannot create in QML"));

    qmlRegisterUncreatableType<MemberList>("Models", 1, 0, "MemberList", QStringLiteral("Only Interface. Cannot create in QML"));
    qmlRegisterType<MemberModel>("Models", 1, 0, "MemberModel");

    MemberList memberList;

    QQmlApplicationEngine engine;
    engine.rootContext()->setContextProperty(QStringLiteral("memberList"), &memberList);

    const QUrl url(u"qrc:/Classcreator/main.qml"_qs);
    QObject::connect(&engine, &QQmlApplicationEngine::objectCreated,
                     &app, [url](QObject *obj, const QUrl &objUrl) {
        if (!obj && url == objUrl)
            QCoreApplication::exit(-1);
    }, Qt::QueuedConnection);

    engine.addImportPath(QCoreApplication::applicationDirPath() + "/qml");
    engine.addImportPath(":/");

    engine.load(url);

    if (engine.rootObjects().isEmpty()) {
        return -1;
    }

    return app.exec();
}

MemberList and Item

class MemberItem
{
public:
    explicit MemberItem();
    MemberItem(const QString name, const QString type, const bool getter, const bool setter, const int protectionLevel);
    ~MemberItem() { }
    MemberItem &operator=(const MemberItem &other);

    QString name() const;
    void setName(const QString &newName);

    QString type() const;
    void setType(const QString &newType);

    bool getter() const;
    void setGetter(bool newGetter);

    bool setter() const;
    void setSetter(bool newSetter);

    int protectionLevel() const;
    void setProtectionLevel(int newProtectionLevel);

private:
    QString m_name;
    QString m_type;
    bool m_getter;
    bool m_setter;
    int m_protectionLevel;
};

class MemberList : public QObject
{
    Q_OBJECT
public:
    explicit MemberList(QObject *parent = nullptr);

    QVector<MemberItem> items() const;

    bool setItemAt(int index, const MemberItem &item);

signals:
    void preItemAppended();
    void postItemAppended();

    void preItemRemoved(int index);
    void postItemRemoved();

public slots:
    void appendItem(const QString &name, const QString &type, const bool getter, const bool setter, const int protectionLevel);
    void removeItemAt(int index);
    int count();

private:
    QVector<MemberItem> m_items;

};

Membermodel

#ifndef MEMBERMODEL_H
#define MEMBERMODEL_H

#include <QObject>
#include "qabstractitemmodel.h"

Q_MOC_INCLUDE("MemberList.h")

class MemberList;

class MemberModel : public QAbstractListModel
{
    Q_OBJECT
    Q_PROPERTY(MemberList *list READ list WRITE setList)

public:
    explicit MemberModel(QObject *parent = nullptr);

    enum {
        NameRole = Qt::UserRole,
        TypeRole,
        GetterRole,
        SetterRole,
        ProtectionLevelRole
    };

    int rowCount(const QModelIndex &parent = QModelIndex()) const override;
    QVariant data(const QModelIndex &index, int role = Qt::DisplayRole) const override;
    bool setData(const QModelIndex &index, const QVariant &value, int role = Qt::EditRole) override;
    Qt::ItemFlags flags(const QModelIndex& index) const override;

    virtual QHash<int,QByteArray> roleNames() const override {
            return { { NameRole, "name" },
                { TypeRole, "type" },
                { GetterRole, "getter" },
                { SetterRole, "setter" },
                { ProtectionLevelRole, "protectionLevel" }
            };
    }

    MemberList *list() const;
    void setList(MemberList *newList);

private:
    MemberList *m_list = nullptr;
};

#endif // MEMBERMODEL_H

App.qml
Screen01 is a UI-file

import QtCore
import QtQuick
import QtQuick.Window
import QtQuick.Controls
import QtQuick.Dialogs
import Qt.labs.settings
import "Delegate"
import "CalcSizeOfElements.js" as Calc
import Backend
import Utils
import Models

Window {
    id: root
    width: Constants.width
    height: Constants.height
    minimumWidth: 1000
    minimumHeight: 400

    BuildClass {
        id: classcreator
    }

// this works properly!
//    ListModel {
//        id: listMemberModel
//    }

// this doesn't work
    MemberModel {
        id: memberModel
        list: memberList
    }

    ListModel {
        id: listFunctionModel
    }

    Component.onCompleted: {
        mainScreen.pathInput.path = Constants.cleanPath(settings.savePath)
    }

    Component.onDestruction: {
        settings.savePath = mainScreen.pathInput.path
    }

    Settings {
        id: settings
        property alias savePath: fileDialog.currentFolder
    }

    Screen01 {
        id: mainScreen
        width: root.width
        height: root.height

        butAddMember.onClicked: {
            memberList.appendItem("m_",
                              mainScreen.textFieldVarTypeText,
                              mainScreen.checkBoxMainGetter.checked,
                              mainScreen.checkBoxMainSetter.checked,
                              0)

             mainScreen.labelMemberText = "Member (%1)".arg(memberList.count())
        }

        listMember.model: memberModel
        listMember.delegate: MemberListDelegate {
            onDeleteItem: function(index) {
                listMemberModel.remove(index)
                mainScreen.labelMemberText = "Member (%1)".arg(models.memberModel.count())
            }
        }

        butAddFunction.onClicked: {
            listFunctionModel.append({
                "retType": mainScreen.textFieldReturnTypeText,
                "name": "",
                "protectionLevel": mainScreen.comboMainProtectionLevel.currentIndex,
                "hidingLevel": mainScreen.comboMainHidingLevel.currentIndex
            })

            mainScreen.labelFunctionText = Calc.setListView(listFunction, "Function")
        }

        listFunction.model: listFunctionModel
        listFunction.delegate: FunctionListDelegate {
            onDeleteItem: function(index) {
                listFunctionModel.remove(index)
                mainScreen.labelFunctionText = Calc.setListView(mainScreen.listFunction, "Function")
            }
        }
    }
}

MemberListDelegate.qml

import QtQuick 2.15
import QtQuick.Controls 2.15
import QtQuick.Layouts 6.3
import Utils
import Models

Item {
    id: item1
    width: parent.width == null ? 400 : parent.width
    height: 40
    property alias buttonDeleteElement: buttonDeleteElement

    signal deleteItem(int index)

    Component.onCompleted: console.log("completed elem... " + name)
    Component.onDestruction: console.log("delete elem... " + name)

    RowLayout {
        id: rowLayout
        anchors.fill: parent

        TextField {
            id: textField1
            Layout.preferredWidth: 50
            Layout.preferredHeight: 28
            placeholderText: qsTr("Type")
            text: type
        }

        TextField {
            id: textField
            Layout.rightMargin: 50
            Layout.fillWidth: true
            Layout.preferredHeight: 28
            placeholderText: qsTr("Membername")
            text: name
            Layout.minimumWidth: 120
        }

        ComboBox {
            id: comboProtectionLevel
            Layout.alignment: Qt.AlignRight | Qt.AlignVCenter
            Layout.preferredWidth: 120
            Layout.preferredHeight: 28
            model: Constants.protectionLevelModel
            currentIndex: protectionLevel
            textRole: "protectionLevel"
        }

        CheckBox {
            id: checkGetter
            text: qsTr("getter")
            Layout.alignment: Qt.AlignRight | Qt.AlignVCenter
            checked: getter
        }

        CheckBox {
            id: checkSetter
            text: qsTr("setter")
            Layout.alignment: Qt.AlignRight | Qt.AlignVCenter
            checked: setter
        }

        Button {
            id: buttonDeleteElement
            Layout.preferredHeight: 28
            Layout.preferredWidth: 28
            icon.source: Constants.getIconFile("action", "ic_delete")
            onClicked: item1.deleteItem(index)

        }
    }
}

Minimal example:
main.cpp

#include <QGuiApplication>
#include <QQmlApplicationEngine>
#include <QtQml/qqmlextensionplugin.h>
#include <QQmlContext>

#include "app_environment.h"
#include "memberlist.h"
#include "membermodel.h"

int main(int argc, char *argv[])
{
    set_qt_environment();

    QGuiApplication app(argc, argv);

    qmlRegisterUncreatableType<MemberList>("Models", 1, 0, "MemberList", QStringLiteral("Only Interface. Cannot create in QML"));
    qmlRegisterType<MemberModel>("Models", 1, 0, "MemberModel");

    MemberList memberList;

    QQmlApplicationEngine engine;
    engine.rootContext()->setContextProperty(QStringLiteral("memberList"), &memberList);

    const QUrl url(u"qrc:/Classcreator/main.qml"_qs);
    QObject::connect(&engine, &QQmlApplicationEngine::objectCreated,
                     &app, [url](QObject *obj, const QUrl &objUrl) {
        if (!obj && url == objUrl)
            QCoreApplication::exit(-1);
    }, Qt::QueuedConnection);

    engine.addImportPath(QCoreApplication::applicationDirPath() + "/qml");
    engine.addImportPath(":/");

    engine.load(url);

    if (engine.rootObjects().isEmpty()) {
        return -1;
    }

    return app.exec();
}

main.qml

import QtQuick
import QtQuick.Controls 6.3
import Models

Window {
    id: root
    height: 400
    visible: true
    color: "#00ffffff"
    minimumWidth: 1000
    minimumHeight: 400

    MemberModel {
        id: memberModel
        list: memberList
    }

    ListView {
        id: listView
        width: 400
        height: 200
        anchors.verticalCenter: parent.verticalCenter
        z: 3
        anchors.horizontalCenter: parent.horizontalCenter
        model: memberModel
        delegate: Item {
            x: 5
            width: 80
            height: 40
            Row {
                id: row1
                Rectangle {
                    width: 40
                    height: 40
                    color: colorCode
                }

                Text {
                    text: name
                    anchors.verticalCenter: parent.verticalCenter
                    font.bold: true
                }
                spacing: 10
            }
        }
    }

    Button {
        id: button
        y: 371
        text: qsTr("Button")
        anchors.left: parent.left
        anchors.bottom: parent.bottom
        anchors.bottomMargin: 8
        anchors.leftMargin: 8
        onClicked: {
            memberList.appendItem("m_",
                               "mainScreen.textFieldVarTypeText",
                               true,
                               true,
                               0)
        }
    }

}

[jeremy_k]

That's a lot of code for a forum post, but I don't see the model implementation, and in particular anything calling QAbstractItemModel::beginInsertRows() and QAbstractItemModel::endInsertRows()

Using the model tester is worth a try.

[Krulle]

@jeremy_k Thanks. I found the error myself tonight. The list had a height of 0.
But I am still surprised that it still worked with a QML ListModel. Is the height automatically increased in this case?

[jeremy_k]

@Krulle said in QML List is not updated by QAbstractListModel:

@jeremy_k Thanks. I found the error myself tonight. The list had a height of 0.

I'm not clear on whether list is referring to the model (which has no on-screen dimensions), or the view (which has defined dimensions in the minimal example portion of the code in the first post. I didn't read all of the code, because it's too long to be a minimal example.

But I am still surprised that it still worked with a QML ListModel. Is the height automatically increased in this case?

There is no automatic size increase. Depending on the circumstances, a child may be overpainting the parent without obvious impact. Eg:

BlueRect.qml:

// Might look ok
Item {
    height: 1
    //default clip = false
    Rectangle {
        height: 100
        border.color: "black"
        border.width: 1
        color: "blue"
    }
}

Repeated.qml:

Repeater {
    model: 2
    // Delegate instances will overlap
    delegate: BlueRect {}
}

[Krulle]

@jeremy_k said in QML List is not updated by QAbstractListModel:

@Krulle said in QML List is not updated by QAbstractListModel:

@jeremy_k Thanks. I found the error myself tonight. The list had a height of 0.

I'm not clear on whether list is referring to the model (which has no on-screen dimensions), or the view (which has defined dimensions in the minimal example portion of the code in the first post. I didn't read all of the code, because it's too long to be a minimal example.

But I am still surprised that it still worked with a QML ListModel. Is the height automatically increased in this case?

There is no automatic size increase. Depending on the circumstances, a child may be overpainting the parent without obvious impact.

Ok, I'll try with a minimal example:

ListModel {
        id: listMemberModel
}

ListView {
        id: listMember
        height: 0
        model: listMemberModel
        delegate: Item { height: 40; Textfield { text: name } }
}

work's with (only QML):

listMemberModel.append({
        "name": "Test"
})

but don't work with a cpp model derived from QAbstractListModel.
If I append an Element via QML-style, the height of the listview is increasing. If i do the same operation from cpp, it doesn't.
Do you have an idea why?

[JonB]

@Krulle
I don't do QML, so only a guess. Is the C++ end emitting a signal when it appends to the model, so that QML will know it has changed?

[jeremy_k]

The QML/Quick views respond to the same signals used by the widget views.