CODEWITHSUNDEEP
c++qtqabstractitemmodelqabstractlistmodel
Hyndrix
Hyndrix

Reputation: 4452

Qt: Remove multiple rows from QAbstractListModel

Is there a way to remove multiple rows, which are not consecutive, efficiently from a QAbstractListModel? Inefficient example:

// Single row removal
void remove (int idx) {
    beginRemoveRows (noParent (), idx, idx);
    // internal remove
    endRemoveRows ();
}

// Remove each row by calling beginRemoveRows multiple times
void removeMultiple (const QList<QObject*> &items) {
    foreach (auto item, items)
    {
        int idx = findIndexInternal(item);
        beginRemoveRows (noParent (), idx, idx);
        // internal remove
        endRemoveRows ();
    }
}

Regards,

Upvotes: 2

Views: 1691

Answers (1)

ntjess
ntjess

Reputation: 1450

See Qt's Model-View reference:

This sequence can be used for any structural update in lieu of the more high-level and convenient protected methods. For example, if a model of two million rows needs to have all odd numbered rows removed, that is 1 million discountiguous ranges of 1 element each. It would be possible to use beginRemoveRows and endRemoveRows 1 million times, but that would obviously be inefficient. Instead, this can be signalled as a single layout change which updates all necessary persistent indexes at once.

It seems you can use layoutAboutToBeChanged() and layoutChanged() to signal large alterations to the underlying model. I haven't tested this yet, though.

Update: I currently use this architecture and it does the trick. You don't even have to signal row removal/addition, since this is handled by the layout signal.

Upvotes: 2

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