我有一个ListView，每个元素都有"name"和"amount"两个角色，我需要统计所有元素的总量并显示出来（例如："A项"：10，"B项"：2.总金额为12）我尝试使用"onDataChanged"，但它显示错误：无法赋值给不存在的属性"onDataChanged"。如何在qml中处理"数据已更改"通知？

• • 主. cpp**

#include <QGuiApplication>
#include <QQmlApplicationEngine>
#include <QStandardItemModel>
#include <QQmlContext>

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

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

    QHash<int, QByteArray> roles;
    roles[Qt::UserRole + 1] = "name";
    roles[Qt::UserRole + 2] = "amount";

    QStandardItemModel *model = new QStandardItemModel();
    model->setRowCount(0);
    model->setItemRoleNames(roles);
    engine.rootContext()->setContextProperty("myModel", model);

    auto item1 = new QStandardItem();
    item1->setData("item1", Qt::UserRole + 1);
    item1->setData("10", Qt::UserRole + 2);
    model->appendRow(item1);

    auto item2 = new QStandardItem();
    item2->setData("item2", Qt::UserRole + 1);
    item2->setData("1", Qt::UserRole + 2);
    model->appendRow(item2);

    engine.load(url);

    return app.exec();
}

• • 主文件. qml**

import QtQuick 2.15
import QtQuick.Window 2.15
import QtQuick.Layouts

Window {
    width: 640
    height: 480
    visible: true
    title: qsTr("Hello World")

    ColumnLayout {
        anchors.fill: parent
        ListView {
            Layout.fillWidth: true
            Layout.fillHeight: true
            model: myModel
            delegate: Text {
                text: name + " " + amount
            }

            onDataChanged: function () {
                var number = 0
                for(var i = 0; i < myModel.rowCount(); i++) {
                    var index = myModel.index(i, 0);
                    number += myModel.data(index, amount)
                }

                total.text = "Total: " + number
            }
        }

        Rectangle {
            Layout.fillWidth: true
            height: 20
            Text {
                id: total
                anchors.fill: parent
                text: "Total: "
            }
        }
    }
}