[Interest] [External]Re: Proxied view not updating live when source model does

Murphy, Sean Sean.Murphy at centauricorp.com
Wed Sep 22 20:54:12 CEST 2021

Thanks for the response, but no, that’s not it. Modifying my baseModel’s setData from
    emit dataChanged(index, index, QVector<int>() << role);
    emit dataChanged(index, index, QVector<int>() << role << Qt::DisplayRole);
changes nothing in the behavior…

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Sent: Wednesday, September 22, 2021 2:46 PM
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Subject: [External]Re: [Interest] Proxied view not updating live when source model does

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You emit dataChanged with the given role (which is Qt::EditRole), but not for Qt::DisplayRole. Is it that?


Am 20.09.2021 um 19:15 schrieb Murphy, Sean:

I'm having an issue where my proxy model and its associated view aren't updating live when changes

are made in the source model.

My proxy model simply is attempting to invert the rows of the source model. So it inherits from a

QSortFilterProxyModel and implements mapFromSource() and mapToSource() as follows:

    QModelIndex invertRowsModel::mapFromSource(const QModelIndex &sourceIndex) const


        if(sourceIndex.isValid() && rowCount() > 0)


            return this->index(rowCount() - sourceIndex.row() - 1, sourceIndex.column());


        return QModelIndex();


    QModelIndex invertRowsModel::mapToSource(const QModelIndex &proxyIndex) const


        if(proxyIndex.isValid() && sourceModel() && rowCount() > 0)


            return sourceModel()->index(rowCount() - proxyIndex.row() - 1, proxyIndex.column());


        return QModelIndex();


I load up my source model with some data, connect the models up to their respective views,

connect the source model to the proxy and launch the application. The original views are

correct - the proxied rows are flipped when compared to the source model. But then if the

user makes a change to some of the data in the source model's view, the corresponding index

in proxy model's view is NOT updated automatically. HOWEVER, if the user then clicks within

the proxy view, or clicks outside of my application, the proxy model will then repaint and the

updated information is correctly shown.

I've attached a minimal example that shows the behavior. Things to note:

1. When the source model emits its dataChanged(), this seems to trigger a dataChanged()

  emission in the proxy model as well. The weird (at least to me) thing is that both of those

  signals have the SAME model index row & column numbers. I would have expected that

  when the source model emits data changed, that the proxy model would translate the

  source model's indices into the proper proxy model's indices via the mapFromSource()

  function and then emit dataChanged() with those indices. I've got debug statements in

  my example to illustrate that no dataChanged() translation is happening - if the user

  updates data in row 0 in the source model's view, the proxy model also emits that data

  changed in its row 0, but that isn't the correct row for the proxy.

2. We discovered that if we connect the proxy model's dataChanged() signal to a custom

  slot within the proxy model, and have that slot emit layoutChanged() then we can get

  the live update behavior when the source model updates. This is at line 25 of

  invertrowsmodel.cpp. It's commented out initially, but if you uncomment it and re-run

  the app then proxy view does update instantly. Other similar signals would work as well -

  we just need something triggers the proxy view to refresh the data in the proxied view,

  but we don't think we should really have to do this...

3. I have a second view attached to the source model and both source model views update

  each other live - changes in one source model view are instantly updated in the other

  source model view, but not in the proxy model view without further user interaction

  (or by emitting that layoutChanged() signal)

Any thoughts as to why the proxy model isn't updating correctly?



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