QML ListView计数为零，只有一些行可见

Question

I have created a ListView model based on QAbstractListModel similar to this example . The problem is my ListView doesn't show all rows, but only those which are initialy visible. So when I scroll (or flick) down theres only black space. ListView has count == 0 but it should have count == 10, since I've added 10 elements.

My class contains the necessary mothods to update the model rowCount

// needed as implementation of virtual method
int rowCount(const QModelIndex & parent) const {
    return standings.size();
}
int rowCount() {
    return standings.size();
}

void addStanding(const Standing &st) {
    beginInsertRows(QModelIndex(), rowCount(), rowCount());
    qDebug() << "row cnt: " << rowCount();
    standings << st;
    endInsertRows();
}

I also update the ListView model

rootContext = (QDeclarativeContext*)(viewer->rootContext());
rootContext->setContextProperty("myModel", &sm);

QML code

ListView {
            id: raceList
            objectName: "standingList"
            y: header.height
            width: parent.width
            height: parent.height - header.height
            clip: true
            model: myModel
            delegate: rowComp
        }
        Component {
            id: rowComp
            SessionRowDelegate { }
        }

I would also like to mention that this works fine with a static model. How to make ListView display all items all the time and not only if visible to user?

SessionRowDelegate

Rectangle {
  id: rowbg
  width: parent.width
  height: 34 * (1 + (parent.width - 360) * 0.002)

  // contains other elements with height not exceeding rowbg's height
  // ...
}

Answer 1

It is a bit late (4 years!), but there is something related to this problem that I have discovered after days of getting stuck! The problem is mainly based in the weird way ListView deals with the models.

After overriding the rowCount method in my own model, I faced the exact problem that you have mentioned. The funny thing is, they are NEVER called. ListView actually never calls to get the rowCount, instead queries for the amount in cacheBuffer size (which defaults to 512 on my system), that is why it won't notice if the items are more than the cacheBuffer size or the default it is using, it only notices that when it is scrolled to the end.

---

While this will shed light on some other people problems, it is not the solution for your problem. In your case, if the items are not that many, I suggest tweaking the ListView cacheBuffer size, and increasing it as much as you need. Just keep in mind that if your elements get numerous, it can have a huge performance penalty.

Answer 2

A ListView only renders the elements that are currently visible plus a few that are pre rendered to be shown when scrolling. The default implementation does not render all of them for performance reasons. Any references to the size of the list should refer to the model object instead of the ListView itself.