questions about datachanged() in model/view programming

[calmspeaker]

When I use tableview to make a table control ,something about singnal dataChanged() really confused me!

If the parameters "const QModelIndex & topLeft, const QModelIndex & bottomRight" are the same index, the view only will update exactly the cell which is pointed by the index.But if topLeft!=bottomRight, the entire tableview will be refreshed no matter whereever the topLeft or bottomRight is.

I looked up the src file of qt, in qabstractitemview.cpp

connect(d->model, SIGNAL(dataChanged(QModelIndex,QModelIndex)),
                this, SLOT(dataChanged(QModelIndex,QModelIndex)));
 
 void QAbstractItemView::dataChanged(const QModelIndex &topLeft, const QModelIndex   &bottomRight)
{
    // Single item changed
    Q_D(QAbstractItemView);
    if (topLeft == bottomRight && topLeft.isValid()) {
        if (d->hasEditor(topLeft)) {
            QAbstractItemDelegate *delegate = d->delegateForIndex(topLeft);
            if (delegate) {
                delegate->setEditorData(d->editorForIndex(topLeft), topLeft);
            }
        }
        if (isVisible() && !d->delayedLayout.isActive()) {
            // otherwise the items will be update later anyway
            d->viewport->update(visualRect(topLeft));
        }
        return;
    }
    d->updateEditorData(topLeft, bottomRight);
    if (!isVisible() || d->delayedLayout.isActive())
        return; // no need to update
 /* ---> */   d->viewport->update(); /* <--- */
}

connect(d->model, SIGNAL(dataChanged(QModelIndex,QModelIndex)),
                this, SLOT(dataChanged(QModelIndex,QModelIndex)));

 void QAbstractItemView::dataChanged(const QModelIndex &topLeft, const QModelIndex   &bottomRight)
{
    // Single item changed
    Q_D(QAbstractItemView);
    if (topLeft == bottomRight && topLeft.isValid()) {
        if (d->hasEditor(topLeft)) {
            QAbstractItemDelegate *delegate = d->delegateForIndex(topLeft);
            if (delegate) {
                delegate->setEditorData(d->editorForIndex(topLeft), topLeft);
            }
        }
        if (isVisible() && !d->delayedLayout.isActive()) {
            // otherwise the items will be update later anyway
            d->viewport->update(visualRect(topLeft));
        }
        return;
    }
    d->updateEditorData(topLeft, bottomRight);
    if (!isVisible() || d->delayedLayout.isActive())
        return; // no need to update
 /* ---> */   d->viewport->update(); /* <--- */
}

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I guess the red code means the entire tableview will be updated! Am I right?

[jacek]

The code invokes update() on the viewport. That's the visible part of the view.