Question

I have a custom delegate derived from QStyleOptionViewItem which is trying to draw multiline (wordwrap) a long line of text in the paint method. After doing some search and Qt doc reading, I looks like I need to use QTextLayout for such task, below is the code I have which still puts the text in one single line, any hints on how to wrapping the line around length of the QStyleOptionViewItem passed in? Thanks!!

void Delegate::paint(QPainter *painter,
                     const QStyleOptionViewItem &option,
                     const QModelIndex &index) const
{
  painter->save();

  painter->translate(option.rect.topLeft());

  QString title = index.data(Qt::DisplayRole).toString();
  QTextLayout * layout = new QTextLayout(title, QApplication::font());

  layout->beginLayout();
  QTextLine line = layout->createLine();
  while (line.isValid()) {
    line.setLineWidth(option.rect.width());
    line = layout->createLine();
  }
 layout->endLayout();
  layout->draw(painter, QPointF(0, 0));

  painter->restore();
}

Since I can’t self answer, I will just post my findings here.
I found couple issues with my code:

1. The test string I are one word consisted of 200 characters and by default QTextLayout does word wrap. So I have to explicitly call QTextLayout::setWrapMode() for that test case to wrap.
2. I am not setting position for each line.

This is my paint method in Ruby:

def paint painter, styleOptionViewItem, modelIndex
  painter.save
  painter.translate styleOptionViewItem.rect.top_left

  marked_text = modelIndex.data(Qt::DisplayRole).value
  font = Qt::Application::font()
  text_layout = Qt::TextLayout.new marked_text
  text_layout.setFont font

  text_option = Qt::TextOption.new
  text_option.setWrapMode(Qt::TextOption::WrapAtWordBoundaryOrAnywhere)
  text_layout.setTextOption text_option

  text_layout.beginLayout
  fm = Qt::FontMetrics.new font
  font_height = fm.height
  i = 0
  while i< LINE_LIMIT do
    line = text_layout.createLine
    break if (!line.isValid())
    line.setLineWidth(styleOptionViewItem.rect.width)
    line.setPosition(Qt::PointF.new(0, font_height * i))
    i += 1
  end
  text_layout.endLayout
  text_layout.draw painter, Qt::PointF.new(0, 0)
  painter.restore
end

Answer 1

I had to do same task for a while.
While I used simple QPainter::drwText, I bumped into this issue.

To make word wrap work, you should:

• disable uniformRowHeight property of view.

• handle sizeHint correctly. By default this function return 0, you should override it to return Qt::SizeHint role of item data.

• But you should also set correct value for Qt::SizeHint role. You can use QFontMetrics::boundingRect to calculate sizeHint, but you should ensure you use same font when calculating sizeHint and when drawing item. On Windows 7 I had an issue, that font of QStandardItem didn’t coincide with QListView‘s one.

  Note, that it is bad idea to calculate sizeHint from scratch every time it requested, because it works really slow.