In a QTableWidget, changing the text color of the selected row - qt

Question

I'm using a QTableWidget to display several rows. Some of these rows should reflect an error and their text color is changed :
Rows reflecting that there is no error are displayed with a default color (black text on white background on my computer).
Rows reflecting that there is an error are displayed with a red text color (which is red text on white background on my computer).
This is all fine as long as there is no selection. As soon as a row is selected, no matter of the unselected text color, the text color becomes always white (on my computer) over a blue background.
This is something I would like to change to get the following :
When a row is selected, if the row is reflecting there is no error, I would like it to be displayed with white text on blue background (default behavior).
If the row is reflecting an error and is selected, I would like it to be displayed with red text on blue background.
So far I have only been able to change the selection color for the whole QTableWidget, which is not what I want !

Answer 1

Answering myself, here is what I ended up doing : a delegate.
This delegate will check the foreground color role of the item. If this foreground color is not the default WindowText color of the palette, that means a specific color is set and this specific color is used for the highlighted text color.
I'm not sure if this is very robust, but at least it is working fine on Windows.
class MyItemDelegate: public QItemDelegate
{
public:
MyItemDelegate(QObject* pParent = 0) : QItemDelegate(pParent)
{
}
void paint(QPainter* pPainter, const QStyleOptionViewItem& rOption, const QModelIndex& rIndex) const
{
QStyleOptionViewItem ViewOption(rOption);
QColor ItemForegroundColor = rIndex.data(Qt::ForegroundRole).value<QColor>();
if (ItemForegroundColor.isValid())
{
if (ItemForegroundColor != rOption.palette.color(QPalette::WindowText))
{
ViewOption.palette.setColor(QPalette::HighlightedText, ItemForegroundColor);
}
}
QItemDelegate::paint(pPainter, ViewOption, rIndex);
}
};
Here is how to use it :
QTableWidget* pTable = new QTableWidget(...);
pTable->setItemDelegate(new MyItemDelegate(this));

Answer 2

What you'll want to do is connect the selectionChanged() signal emitted by the QTableWidget's QItemSelectionModel to a slot, say OnTableSelectionChanged(). In your slot, you could then use QStyleSheets to set the selection colours as follows:
if (noError)
{
pTable->setStyleSheet("QTableView {selection-background-color: #000000; selection-color: #FFFFFF;}");
}
else
{
pTable->setStyleSheet("QTableView {selection-background-color: #FF0000; selection-color: #0000FF;}");
}

Answer 3

It looks ok, but you might want to look at the documentation of QStyleOption it can tell you wether the item drawn is selected or not, you don't have to look at the draw color to do that. I would probably give the model class a user role that returns whether the data is valid or not and then make the color decision based on that. I.e. rIndex.data(ValidRole) would return wether the data at this index is valid or not.
I don't know if you tried overriding data for the BackgroundRole and returning a custom color, Qt might do the right thing if you change the color there

Answer 4

You could, of course, inherit from the table widget and override the paint event, but I don't think that is what you want to do.
Instead, should use the QAbstractItemDelegate functionality. You could either create one to always be used for error rows, and set the error rows to use that delegate, or make a general one that knows how to draw both types of rows. The second method is what I would recommend. Then, your delegate draws the rows appropriately, even for the selected row.

Answer 5

You could use e.g. a proxy model for this where you return a different color if you have an error for the specific modelindex;
QVariant MySortFilterProxyModel::data(const QModelIndex & index, int role = Qt::DisplayRole) {
// assuming error state and modelindex row match
if (role==Qt::BackgroundRole)
return Qt::red;
}