Qml Listview在重置模型时保留视图

Question

我有一个qml listview，它有一个来自C++的模型。数据从另一个线程生成并更新到C++代码模型。之后，我使用BeginResetModel()来更新qml中的listview。除了qml中的视图之外，所有的工作都开始了，但是我希望listview保持当前视图而不改变视图。

MWE：

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::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(); 
} 

的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 
     } 
    } 
} 

Answer 1

从我看到的，我有几个建议，但我没有测试它，所以它可能或现在可以工作。

• 我看到你只能追加数据，所以为什么重置模型时可以逐一插入行并使用beginInsertRows() and endInsertRows()方法呢？
• 如果这没有帮助，你可以连接QML到modelAboutToBeReset()模型的信号（为此编写一个处理程序onModelAbouttoBeReset），并在复位前保存当前索引，然后在复位模型后，使用处理程序onModelReset来定位你在这个索引下的listview通过调用'positionViewAtIndex（index，mode）'的方法ListView

PS您必须在电话beginResetModel()和endResetModel()之间更改模型