QML TreeView not updating at runtime after adding

问题:

I have a QML TreeView that gets data through a QStandardItemModel. When the application is running, I press a button which adds a new entry. I know the data is changing, but the QML TreeView is not updating. I've also tried beginResetModel() and endResetModel(). The data is correctly displayed in the TreeView upon loading the application, but the TreeView does not change when modifying the data in the model.

treeviewmodel.cpp

#include <QDebug>
#include <QStandardItemModel>
#include "treeviewmodel.h"

TreeViewModel::TreeViewModel(QObject *parent) :
    QStandardItemModel(parent)
{
    m_roleNameMapping[TreeViewModel_Role_Name] = "name_role";

    QStandardItem* entry;
    entry = new QStandardItem(QString("my_entry"));
    entry->setData("abc", TreeViewModel_Role_Name);

    auto childEntry = new QStandardItem( "my_child_entry" );
    childEntry->setData( "def",TreeViewModel_Role_Name);
    entry->appendRow(childEntry);
    appendRow( entry );

}
TreeViewModel& TreeViewModel::Instance()
{
    static TreeViewModel instance; //Guaranteed to be destroyed
    return instance;
}
void TreeViewModel::addEntry()
{
    qDebug () << "Adding entry...";

    QStandardItem* entry;
    entry = new QStandardItem(QString("my_entry"));
    entry->setData("Second Entry", TreeViewModel_Role_Name);
    auto childEntry = new QStandardItem( "my_child_entry" );
    childEntry->setData( "Second Entry Child",TreeViewModel_Role_Name);
    entry->appendRow(childEntry);
    appendRow( entry );
    qDebug () << rowCount(); //Increases everytime I call the function
                             //Data is being added
}
QHash<int, QByteArray> TreeViewModel::roleNames() const
{
    return m_roleNameMapping;
}

main.qml

import treeModel 1.0
...
MyTreeModel {
    id: theModel
}

//Left Tree View
Rectangle {
    id: leftView
    Layout.minimumWidth: 50
    width: 200
    //Layout.fillWidth: true
    color: "white"
    TreeView {
        id: treeView
        anchors.fill: parent
        model: theModel
        TableViewColumn {
            role: "name_role"
            title: "Name"
        }
        TableViewColumn {
            role: "description_role"
            title: "Description"
        }
    }
}

ToolButton {
    iconSource: "lock.png"
    onClicked: {
    treeviewmodel.addEntry()
    }
}

main.cpp

QQmlContext* treeViewModelCtx = engine.rootContext();
treeViewModelCtx->setContextProperty("treeviewmodel", &TreeViewModel::Instance());

//Register types
qmlRegisterType<TreeViewModel>("treeModel", 1, 0, "MyTreeModel" );

回答1:

I hope this example helps. Unfortunately, I don't have your whole code to see where the problem is.

Maybe the keys are the data and roleNames methods.

In this example, we also have a button called addButton to add new items.

main.cpp

#include "animalmodel.h"

#include <QGuiApplication>
#include <QQmlApplicationEngine>
#include <qqmlcontext.h>
#include <qqml.h>

int main(int argc, char ** argv)
{
    QGuiApplication app(argc, argv);

    AnimalModel model;
    model.addAnimal("Wolf", "Medium");
    model.addAnimal("Polar bear", "Large");
    model.addAnimal("Quoll", "Small");

    QQmlApplicationEngine engine;

    QQmlContext *ctxt = engine.rootContext();
    ctxt->setContextProperty("myModel", &model);

    engine.load(QUrl(QStringLiteral("qrc:/view.qml")));

    return app.exec();
}

animalmodel.h

#ifndef ANIMALMODEL_H
#define ANIMALMODEL_H

#include <QStandardItemModel>

class AnimalModel : public QStandardItemModel
{
    Q_OBJECT
public:
    enum AnimalRoles {
        TypeRole = Qt::UserRole + 1,
        SizeRole
    };

    AnimalModel(QObject *parent = 0);

    Q_INVOKABLE void addAnimal(const QString &type, const QString &size);

    QVariant data(const QModelIndex & index, int role = Qt::DisplayRole) const;

protected:
    QHash<int, QByteArray> roleNames() const;
};

#endif // ANIMALMODEL_H

animalmodel.cpp

#include "animalmodel.h"

AnimalModel::AnimalModel(QObject *parent)
    : QStandardItemModel(parent)
{

}

void AnimalModel::addAnimal(const QString &type, const QString &size)
{
    QStandardItem* entry = new QStandardItem();
    entry->setData(type, TypeRole);

    auto childEntry = new QStandardItem();
    childEntry->setData(size, SizeRole);
    entry->appendRow(childEntry);

    appendRow( entry );
}

QVariant AnimalModel::data(const QModelIndex & index, int role) const {
    QStandardItem *myitem = itemFromIndex(index);

    if (role == TypeRole)
        return myitem->data(TypeRole);
    else if (role == SizeRole) {
        if (myitem->child(0) != 0)
        {
            return myitem->child(0)->data(SizeRole);
        }
    }

    return QVariant();
}

QHash<int, QByteArray> AnimalModel::roleNames() const {
    QHash<int, QByteArray> roles;
    roles[TypeRole] = "type";
    roles[SizeRole] = "size";
    return roles;
}