Changing the row background color of a QTreeView does not work

Question

I have a QTreeView and want different background colors for rows, depending on their content. To achieve this, I derived a class MyTreeView from QTreeView and implemented the paint method as follows:

    void MyTreeView::drawRow (QPainter* painter,
                              const QStyleOptionViewItem& option,
                              const QModelIndex& index) const
    {
      QStyleOptionViewItem newOption(option);

      if (someCondition)
      {
        newOption.palette.setColor( QPalette::Base, QColor(255, 0, 0) );
        newOption.palette.setColor( QPalette::AlternateBase, QColor(200, 0, 0) );
      }
      else
      {
        newOption.palette.setColor( QPalette::Base, QColor(0, 0, 255) );
        newOption.palette.setColor( QPalette::AlternateBase, QColor(0, 0, 200) );
      }

      QTreeView::drawRow(painter, newOption, index);
    }

Initially, I set setAlternatingRowColors(true); for the QTreeView.

My problem: Setting the color for QPalette::Base has no effect. Every second row remains white.

However, setting QPalette::AlternateBase works as expected. I tried setAutoFillBackground(true) and setAutoFillBackground(false) without any effect.

Are there any hints how to solve this problem? Thank you.

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Remark: Setting the color by adapting MyModel::data(const QModelIndex&, int role) for Qt::BackgroundRole does not provide the desired result. In this case, the background color is used only for a part of the row. But I want to color the full row, including the left side with the tree navigation stuff.

Qt Version: 4.7.3

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Update: For unknown reasons QPalette::Base seems to be opaque. setBrush does not change that. I found the following workaround:

    if (someCondition)
    {
        painter->fillRect(option.rect, Qt::red);
        newOption.palette.setBrush( QPalette::AlternateBase, Qt::green);
    }
    else
    {
        painter->fillRect(option.rect, Qt::orange);
        newOption.palette.setBrush( QPalette::AlternateBase, Qt:blue);
    }

Answer 1

If the only problem is that the expanding/collapsing controls do not have a background like rest of the row then use Qt::BackgroundRole in ::data() of your model (as described by pnezis in their answer) and add this to your tree view class:

void MyTreeView::drawBranches(QPainter* painter,
                              const QRect& rect,
                              const QModelIndex& index) const
{
  if (some condition depending on index)
    painter->fillRect(rect, Qt::red);
  else
    painter->fillRect(rect, Qt::green);

  QTreeView::drawBranches(painter, rect, index);
}

I've tested this on Windows (Vista and 7) using Qt 4.8.0 and expanding/collapsing arrows have proper background. The problem is that those arrows are part of the view and thus cannot be handled in a model.

Answer 2

Instead of subclassing QTreeView you should handle the background color through your model. Use the data() function and the Qt::BackgroundRole for changing the background color of the rows.

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

   if (role == Qt::BackgroundRole)
   {
       if (condition1)
          return QColor(Qt::red);
       else
          return QColor(Qt::green); 
   }

   // Handle other roles

   return QVariant();
}