Qml Listview在重置模型时保留视图

问题描述

我有一个qml listview，它具有c ++的模型.数据从另一个线程生成，并更新为c ++代码模型.之后，我使用 BeginResetModel()来更新qml中的listview.一切正常，除了qml中的视图是从头开始的，但是我希望listview保留当前视图而不更改视图.

I have a qml listview which have a model from c++. The data is generated from another thread and update to model in c++ code. After that, I used BeginResetModel() to update listview in qml. Everything works except the view in qml go the the beginning, but I want the listview keep the current view without changing view.

MWE:

listviewelement.cpp

listviewelement.cpp

ListViewElement::ListViewElement(int id,QString attr):m_id(id),m_attr(attr)
{

}

int ListViewElement::getId()
{
    return m_id;
}

QString ListViewElement::getAttr()
{
    return m_attr;
}

listviewmodel.cpp

listviewmodel.cpp

ListViewModel::ListViewModel(QObject *parent): QAbstractListModel(parent)
  , m_items(new QList<ListViewElement*>()){

}


QHash<int,QByteArray> ListViewModel::roleNames() const
{
    qDebug() << Q_FUNC_INFO;
    QHash<int,QByteArray> roles;
    roles[ListViewEnum::ID] = "id";
    roles[ListViewEnum::ATTR] = "attr";
    return roles;
}

QVariant ListViewModel::data(const QModelIndex &index, int role) const
{
    if (!index.isValid() || index.row() > m_items->size()-1)
        return QVariant();

    ListViewElement *dobj = m_items->at(index.row());

    if (!dobj)
        return QVariant();

    switch (role) {
    case ListViewEnum::ID:
        return QVariant::fromValue(dobj->getId());
    case ListViewEnum::ATTR:
        return QVariant::fromValue(dobj->getAttr());
    default:
        return QVariant();
    }
}

int ListViewModel::rowCount(const QModelIndex &parent) const
{
    Q_UNUSED(parent)
    return m_items? m_items->size(): 0;
}

void ListViewModel::generateData()
{
    ListViewElement *ele = new ListViewElement(1,"attribute");
    m_items->append(ele);
    beginResetModel();
    endResetModel();
}

main.cpp

#include <QGuiApplication>
#include <QQmlApplicationEngine>
#include "listviewmodel.h"
#include <QQmlContext>
#include <QTimer>

int main(int argc, char *argv[])
{
    ListViewModel model;
    QTimer *timer = new QTimer();
    QGuiApplication app(argc, argv);

    QQmlApplicationEngine engine;
    engine.rootContext()->setContextProperty("listViewModel",&model);
    engine.load(QUrl(QStringLiteral("qrc:/main.qml")));

    QObject::connect(timer,SIGNAL(timeout()),&model,SLOT(generateData()));

    timer->start(1000);
    return app.exec();
}

main.qml

import QtQuick 2.5
import QtQuick.Window 2.2

Window {
    id: appMain
    visible: true
    width: 640
    height: 480
    title: qsTr("Hello World")
    color: "#FFFF88"

    ListView {
        id: mainListView
        width: parent.width
        height: parent.height
        spacing: 10
        highlight: Rectangle {color: "green";radius: 5; focus: true}
        highlightFollowsCurrentItem: true
        focus: true
        cacheBuffer: 100
        model: listViewModel
        delegate: Rectangle {
            width: parent.width
            height: 35
            color: "transparent"
            Text {
                text: "\t" + id + "\t" + attr
            }

            MouseArea {
                width: parent.width
                height: parent.height
                onClicked: {
                    console.log("click item" + index)
                    mainListView.currentIndex = index
                }
            }
        }
    }

    Item {
        id: scrollBar
        width: 12; height: mainListView.height
        anchors.left: mainListView.left
        opacity: 0.7
        property real position: mainListView.visibleArea.yPosition
        property real pageSize: mainListView.visibleArea.heightRatio/2
        property int orientation: Qt.Vertical
        visible: true

        Rectangle {
            id: background
            anchors.fill: parent
            radius: scrollBar.orientation == Qt.Vertical ? (width/2 - 1) : (height/2 - 1)
            color: "white"
            opacity: 1.0
        }

        Rectangle {
            x: scrollBar.orientation == Qt.Vertical ? 1 : (scrollBar.position *(scrollBar.width - 2) + 1)
            y: scrollBar.orientation == Qt.Vertical ? (scrollBar.position *(scrollBar.height - 2) + 1) : 1
            width: scrollBar.orientation == Qt.Vertical ? (parent.width - 2) : (scrollBar.pageSize * (scrollBar.width - 2))
            height: scrollBar.orientation == Qt.Vertical ? (scrollBar.pageSize * (scrollBar.height - 2)) : (parent.height - 2)
            radius: scrollBar.orientation == Qt.Vertical ? (width/2 - 1) : (height/2 - 1)
            color: "black"
            opacity: 0.2
        }
    }
}

推荐答案

从我的观察中，我有一些建议，尽管我没有对其进行测试，所以它可能会起作用，也可能不会起作用.

From what I see, I have several suggestions, though I didn't test it, so it might or might not work.

• 我看到您仅附加数据，那么为什么可以一一插入行并为此使用 beginInsertRows()和endInsertRows()方法来重置模型?
• 如果这样做没有帮助，则可以在QML中连接到模型的 modelAboutToBeReset()信号(为此编写一个处理程序 onModelAbouttoBeReset )并保存当前索引在重置之前，然后在重置模型之后，使用处理程序 onModelReset 通过调用 ListView 的"positionViewAtIndex(index，mode)"方法将此列表视图定位在此索引处li>

• I see that you only append data, so why reset the model when you can insert rows one by one and use beginInsertRows() and endInsertRows() methods for that?
• If that doesn't help, you might connect in QML to modelAboutToBeReset() signal of the model (write a handler onModelAbouttoBeReset for that) and save your current index before reset, then after you reset the model, use a handler onModelReset to position your listview at this index by calling 'positionViewAtIndex(index, mode)' method of ListView

P.S.您必须在调用 beginResetModel()和 endResetModel()

P.S. You must change your model between the calls beginResetModel()and endResetModel()

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