How can I change QTableView's color of the area that doesn't have cells on it?

giesbert

if you use a proxy model, the proxy models data method is called for each data query instead of the methods of the original model. This then calls the original (source) model. So you can do everything you want there, like changing backroundColor via the Qt::BackgroundRole. IMHO ProxyModels are easier then derived SQL models ;-)

Edico

Gerolf, this mean that I must subclass QSortFilterProxyModel and reimplement data() method?

octal

Yes, you can create your custom ProxyModel by sublcassing QSortFilterProxyModel and reimplementing the data() method. From there, you can do everything you want, like Gerolf said.

Finally, you just set the sourceModel of your ProxyModel, and it should work :)

andre

Yes. If you were using 4.8, I would suggest you use -QIdentityModel- [[doc:QIdentityProxyModel]] as your base class, but if you are still on 4.7, use [[doc:QSortFilterProxyModel]] instead. You only need to reimplement the data() method. In that method, you only need to implement the case where the Qt::BackgroundRole is requested. Based on the row number (odd or even), you can return a different color. For all other cases, you get the parent QModelIndex by calling mapToSource() on the model index, and then return the result of calling the data() method on the source model with the same role and the model index you just mapped.

octal

bq. For all other cases, you get the parent QModelIndex by calling mapToSource() on the model index, and then return the result of calling the data() method on the source model with the same role and the model index you just mapped.

Or just calling the base class method ? Like :

@
QVariant MyProxyModel::data(const QModelIndex &index, int role)
{
if (role == Qt::BackgroundRole)
{
return ...
}

return QSortFilterProxyModel::data(index, role);

@

bq. If you were using 4.8, I would suggest you use QIdentityModel as your base class

I made a research and I guess you meant "QIdentityProxyModel":http://doc.trolltech.com/4.8-snapshot/qidentityproxymodel.html

Interesting :)

andre

Yes, I guess you can also call the base class implementation. That does the same:

@
Q_D(const QSortFilterProxyModel);
QModelIndex source_index = mapToSource(index);
if (index.isValid() && !source_index.isValid())
return QVariant();
return d->model->data(source_index, role);
@

I guess it does not matter much.

Edico

I've set the outside area of the cells like that:

@
QPalette p = view->palette();
QColor color = p.color(QPalette::Window);
p.setColor(QPalette::Base, color);
view->setPalette(p);
@

Then data() in MyProxyModel:

@
QVariant MyProxyModel::data(const QModelIndex &index, int role) const
{
if (!index.isValid())
return QVariant::Invalid;

int row = index.row();

QWidget widget;  // I didn't found a wiser method to obtain the palette colors than creating a QWidget inside the data() method
QColor alternateColor1 = widget.palette().color(QPalette::AlternateBase);
QColor alternateColor2 = widget.palette().color(QPalette::Base);

if (role == Qt::BackgroundRole) {
    QBrush rowBackground;
    if (row % 2 == 0)
        rowBackground = QBrush(alternateColor1);
    else if (row % 2 != 0)
        rowBackground = QBrush(alternateColor2);
    return rowBackground;
}
return QSortFilterProxyModel::data(index, role);

}
@

It does what I wanted.
Thank you all for the help.

andre

The data method is called very frequently. It is not a good idea to create a widget in this method. Instead, why not just create a pair of getters and setter methods for the colors on the proxy model. Set them once when you create the proxy, and use them in your data method. That will be much more performant.

Edico

I know it's a little bit outside the subject but, how is much better:
to have setters like this:

@
void MyProxyModel::setAlternateColor1()
{
QWidget widget;
alternateColor1 = widget.palette().color(QPalette::Base);
}

void MyProxyModel::setAlternateColor2()
{
QWidget widget;
alternateColor2 = widget.palette().color(QPalette::AlternateBase);
}
@

and data() calling the getters,
or setting the colors in the constructor like this:

@
MyProxyModel::MyProxyModel()
{
QWidget widget;
alternateColor1 = widget.palette().color(QPalette::Base);
alternateColor2 = widget.palette().color(QPalette::AlternateBase);
}
@

and data using directly QColor alternateColor1 and QColor alternateColor2?

octal

I think you misunterstood what Andre meant.

bq. Instead, why not just create a pair of getters and setter methods for the colors on the proxy model.

A pair of getters/setters would be :

@
void MyProxyModel::setAlternateColor1(const QColor &color)
{
mAlternateColor1 = color;
}

QColor MyProxyModel::alternateColor1() const
{
return mAlternateColor1;
}
@

andre

Octal:
Indeed, that's what I meant, and also a getter and a setter for the primary color. You can set them at initialization of your proxy model, which is very likely to be in the constructor of a widget class. Hence, you have cheap access to a widget pointer and the palette there, and you only need that access once.

Edico

I've created setters and getters. Now I use the proxy like that:

@
proxyModel = new MyProxyModel;
QColor altColor1 = this->palette().color(QPalette::Base);
QColor altColor2 = this->palette().color(QPalette::AlternateBase);
proxyModel->setAlternateColor1(altColor1);
proxyModel->setAlternateColor2(altColor2);
proxyModel->setSourceModel(model);
@

proxyModel's data() method calls the getters.
Is it better like that?

Andre, what do you mean with primary color?

andre

As long as you use the colors you set there in your data() method: much better :-)

One small tip: you will want to give your MyProxyModel object a parent object. Seeing that this proxy is really doing presentation work, I suggest you use the view that it is for as the parent object. Also: a more descriptive name than "MyProxyModel" would probably work better in the long run.

Edico

I've called it PresentationProxyModel :-)
Thanks a lot for the help.

alexisdm

The presentation details should normally be handled by the delegates, for example:
@class AlternateBackgroundColorDelegate : public QStyledItemDelegate {
QColor colors[2];
public:
AlternateBackgroundColorDelegate(const QColor & color1,
const QColor & color2,
QObject *parent = 0)
: QStyledItemDelegate(parent)
{
colors[0] = color1;
colors[1] = color2;
}
void initStyleOption(QStyleOptionViewItem *option,
const QModelIndex &index) const
{
QStyledItemDelegate::initStyleOption(option, index);

    QStyleOptionViewItemV4 *optionV4 =
            qstyleoption_cast<QStyleOptionViewItemV4*>(option);
    // If the brush hasn't explicitly been set in the model
    if (optionV4->backgroundBrush.style() == Qt::NoBrush)
        optionV4->backgroundBrush = QBrush(colors[index.row()%2]);
}

};

// And you use it like this:
tableView->setItemDelegate(
new AlternateBackgroundColorDelegate(Qt::blue, Qt::red, tableView));
@
Or using a different palette for the items and the view:
@class ChangePaletteDelegate : public QStyledItemDelegate {
QPalette palette;
public:
ChangePaletteDelegate(const QPalette &palette,
QObject *parent = 0)
: QStyledItemDelegate(parent), palette(palette)
{
}
void initStyleOption(QStyleOptionViewItem *option,
const QModelIndex &index) const
{
QStyledItemDelegate::initStyleOption(option, index);
option.palette = palette;
// Edit: the palette isn't used for background color if QPalette::Base is set
QStyleOptionViewItemV4 optionV4 =
qstyleoption_cast<QStyleOptionViewItemV4>(option);
// If the brush has explicitly been set in the model, do nothing
if (optionV4->backgroundBrush.style() != Qt::NoBrush)
return;

    if(optionV4->features & oQStyleOptionViewItemV2::Alternate) {
        optionV4->backgroundBrush = palette.brush(QPalette::AlternateBase);
    } else {
        optionV4->backgroundBrush = palette.brush(QPalette::Base);
    }
}

};

// And you use it like this:
QPalette palette = tableView->palette();
// Use the original palette here, for the items
tableView->setItemDelegate(new ChangePaletteDelegate(palette, tableView));
// and change the background for the view
palette.setColor(QPalette::Base, Qt::yellow);
tableView->setPalette(palette);

@

Edit Fixed ChangePaletteDelegate.

Edico

alexisdm, l like your way for solving this problem.
The palette method doesn't work for me.

alexisdm

The palette method only works if you don't use stylesheets at the same time, I think.

Edico

I don't use stylesheets. With ChangePaletteDelegate I have the cells and the outside area of the cells yellow (other color for the alternating row color);

alexisdm

Sorry, I fixed it. It was only working if the QPalette::Base wasn't set explicitly.
The alternate row background is painted directly by the view, and not by the delegate as I thought.
So in both methods, QStyleOptionViewItemV4::backgroundBrush must be used to change the background color.

krisztiantobias

It's a really old topic, but still usable so: for the empty space below the cells you can use the viewport:

tableWidget->viewport()->setStyleSheet("background-color: #888;");