how to color a cell in a QTableView

[JeanC]

Got it working thanks
For those interested my code:

in the .h file add:

class Delegate : public QItemDelegate
 {
 Q_OBJECT
 public:
 Delegate(QWidget *parent = 0) : QItemDelegate(parent) {}
 void paint(QPainter *painter, const QStyleOptionViewItem &option,
                const QModelIndex &index) const;
 };

class Delegate : public QItemDelegate
 {
 Q_OBJECT
 public:
 Delegate(QWidget *parent = 0) : QItemDelegate(parent) {}
 void paint(QPainter *painter, const QStyleOptionViewItem &option,
                const QModelIndex &index) const;
 };

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in the .cpp, in a constructor

table->setItemDelegate(new Delegate);

table->setItemDelegate(new Delegate);

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and the event:

//---------------------------------------------------
void Delegate::paint(QPainter *painter, const QStyleOptionViewItem &option,
                          const QModelIndex &index) const
{
QString val;
if (qVariantCanConvert<QString>(index.data()))
    val = qVariantValue<QString>(index.data());
if (val == "1")
	{
  painter->fillRect(option.rect, option.palette.highlight());
	}
else
  QItemDelegate::paint(painter, option, index);
}

//---------------------------------------------------
void Delegate::paint(QPainter *painter, const QStyleOptionViewItem &option,
                          const QModelIndex &index) const
{
QString val;
if (qVariantCanConvert<QString>(index.data()))
    val = qVariantValue<QString>(index.data());
if (val == "1")
	{
  painter->fillRect(option.rect, option.palette.highlight());
	}
else
  QItemDelegate::paint(painter, option, index);
}

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[aamer4yu]

I was wondering if QTableWidgetItem::setBackground could be of some use in this case ??

one can get the tablewidgetitem(the cell) and set the bacground to it.

[smacchia]

Using the delegate works fine if I want to color the text. But I need to color the background of specific cells in the table. I have the following in my delegate:

void MyDelegate::paint(
	QPainter                     *painter, 
	QStyleOptionViewItem const &  option,
        QModelIndex          const &  index) const
{
    QStyleOptionViewItem opt(option);
 
	if (index.column() == _colorColumn)
	{
    	opt.palette.setColor(
        	QPalette::Base, 
        	QColor(255, 255, 204));
 
    	opt.palette.setColor(
        	QPalette::Window, 
        	QColor(255, 255, 204));		
	}
 
	return QItemDelegate::paint(painter, opt, index);	
}

void MyDelegate::paint(
	QPainter                     *painter, 
	QStyleOptionViewItem const &  option,
        QModelIndex          const &  index) const
{
    QStyleOptionViewItem opt(option);
	
	if (index.column() == _colorColumn)
	{
    	opt.palette.setColor(
        	QPalette::Base, 
        	QColor(255, 255, 204));
		
    	opt.palette.setColor(
        	QPalette::Window, 
        	QColor(255, 255, 204));		
	}

	return QItemDelegate::paint(painter, opt, index);	
}

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Where _colorColumn is the column that I want the background colored. It's a member variable that gets initialized in the delegate's ctor.

And it's not working. Any ideas what I can do next?

[squidge]

Wouldn't it be easier to define a model and use Qt::BackgroundColorRole and Qt::TextColorRole in the 'data' method with the default delegate?

Eg.

if (role == Qt::TextColorRole) {
if (index.column() == _colorColumn) {
        return Qt::red;
    }
}
if (role == Qt::BackgroundColorRole) {
if (index.column() == _colorColumn) {
        return Qt::blue;
    }
}

if (role == Qt::TextColorRole) {
if (index.column() == _colorColumn) {
        return Qt::red;
    }
}
if (role == Qt::BackgroundColorRole) {
if (index.column() == _colorColumn) {
        return Qt::blue;
    }
}

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[sosanjay]

Hi,

You can do it simply by using setForeground() for text color and setBackground() for cell background color.

By using

tbl_item = new QTableWidgetItem (QTableWidgetItem (QString (SList.at(0))));
tbl_item->setBackground(QBrush(QColor(Qt::blue)));



I think it is useful for You.

[smacchia]

This won't work for me because I'm not use QTableWidget. I'm using QTableView with my own table model.

As I said, changing the color of the text using the QPalette::WindowText works. It's changing the background of the table that isn't taking effect. Neither QPalette::Base or QPalette:Window work.

[smacchia]

Wouldn't it be easier to define a model and use Qt::BackgroundColorRole and Qt::TextColorRole in the 'data' method with the default delegate?

Eg.

if (role == Qt::TextColorRole) {
if (index.column() == _colorColumn) {
        return Qt::red;
    }
}
if (role == Qt::BackgroundColorRole) {
if (index.column() == _colorColumn) {
        return Qt::blue;
    }
}

if (role == Qt::TextColorRole) {
if (index.column() == _colorColumn) {
        return Qt::red;
    }
}
if (role == Qt::BackgroundColorRole) {
if (index.column() == _colorColumn) {
        return Qt::blue;
    }
}

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I tried this and it also didn't work

[smacchia]

Well believe it or not I got it to work using the role and the ::data method. However, I had to respond to a role of Qt::BackgroundRole, not Qt::BackgroundColorRole (I figured this out by looking at the Qt source for qitemdelegate.cpp). This is what worked:

if (role == Qt::BackgroundRole && index.column() == _colorColumn)
    return QColor(255,255,204);

if (role == Qt::BackgroundRole && index.column() == _colorColumn)
    return QColor(255,255,204);

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[woodja]

I used the QModelIndex's model to color the cell using the setData method that was mentioned above, but as part of slot rather than a delegate. This will highlight whatever cell the user clicks on.

void MyParentWidget::init()
{
	connect(((QAbstractItemView*)this->table), SIGNAL(pressed(const QModelIndex&)), 
               this, SLOT(highlightCell(const QModelIndex&)));
}

void MyParentWidget::init()
{
	connect(((QAbstractItemView*)this->table), SIGNAL(pressed(const QModelIndex&)), 
               this, SLOT(highlightCell(const QModelIndex&)));
}

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void MyParentWidget::highlightCell(const QModelIndex &cellIndex)
{
    for(int i=0; i<cellIndex.model()->columnCount(); i++)
    {
      for(int j=0; j<cellIndex.model()->rowCount(); j++)
      {
		if(i == cellIndex.column() && j == cellIndex.row())
		{
			((QStandardItemModel*)cellIndex.model())->item(cellIndex.row(), i)->setData(QBrush(Qt::yellow), 
                               Qt::BackgroundRole);
		}
		else
		{
			((QStandardItemModel*)cellIndex.model())->item(cellIndex.row(), i)->setData(QBrush(Qt::white), 
                              Qt::BackgroundRole);
		}
      }
    }
}

void MyParentWidget::highlightCell(const QModelIndex &cellIndex)
{
    for(int i=0; i<cellIndex.model()->columnCount(); i++)
    {
      for(int j=0; j<cellIndex.model()->rowCount(); j++)
      {
		if(i == cellIndex.column() && j == cellIndex.row())
		{
			((QStandardItemModel*)cellIndex.model())->item(cellIndex.row(), i)->setData(QBrush(Qt::yellow), 
                               Qt::BackgroundRole);
		}
		else
		{
			((QStandardItemModel*)cellIndex.model())->item(cellIndex.row(), i)->setData(QBrush(Qt::white), 
                              Qt::BackgroundRole);
		}
      }
    }
}

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You can modify & extend this behavior to meet your needs.

[venomj]

just overide the data function in your model, it looks like this

QVariant MyTestModel::data(const QModelIndex &index, int role) const
{
    switch(role)
    {
    case Qt::DisplayRole:
        return QVariant(QString(tr("%1")).arg((index.column() + 1) * 1000 + index.row() + 1));
    case Qt::BackgroundRole:
        switch(index.column() % 3)
        {
        case 0:
            return QVariant(QColor(Qt::red));
        case 1:
            return QVariant(QColor(Qt::green));
        case 2:
            return QVariant(QColor(Qt::blue));
        default://only to disable warning
            return QVariant(QColor(Qt::white));
        }
 
        break;
    default:
        return QVariant();
    }
}

QVariant MyTestModel::data(const QModelIndex &index, int role) const
{
    switch(role)
    {
    case Qt::DisplayRole:
        return QVariant(QString(tr("%1")).arg((index.column() + 1) * 1000 + index.row() + 1));
    case Qt::BackgroundRole:
        switch(index.column() % 3)
        {
        case 0:
            return QVariant(QColor(Qt::red));
        case 1:
            return QVariant(QColor(Qt::green));
        case 2:
            return QVariant(QColor(Qt::blue));
        default://only to disable warning
            return QVariant(QColor(Qt::white));
        }

        break;
    default:
        return QVariant();
    }
}

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the BackgroundRole for the item's background color
the ForegroundRole for the text color

[SykeS]

Reassuming:

How to set font-color to red if value in specified cell is for example not in specified range (int)?

[pilpi]

Just a sidenote - from a usability point of view, in a majority of cases you probably don't want to paint the entire background.

Screenshot: 2015-09-09 13_37_16-voima - Forceproof Analyst.png

In many cases, using a Qt:: DecorationRole is more aesthetic and less obtrusive than filling the entire cell background. The text is still readable; you don't have to think about the contrast between changed foreground and background colours, since DecorationRole only paints a small rectangle of the color you selected, inside the cell.

QVariant MyModel::data(const QModelIndex &index, int role) const
{
        int column=index.column();
        if((role==Qt::DecorationRole)){
            if(column==firstVisibleColumnIndex){
                // figure out correct color for current row here
                return QColor(100,255,255);
            }
         }
}

QVariant MyModel::data(const QModelIndex &index, int role) const
{
        int column=index.column();
        if((role==Qt::DecorationRole)){
            if(column==firstVisibleColumnIndex){
                // figure out correct color for current row here
                return QColor(100,255,255);
            }
         }
}

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