Crazy QPlainTextEdit::document() behavior

[Lykurg]

Hi,

I have following class (simplified...):

class MyLabel : public QLabel
{
    Q_OBJECT
  public:
    explicit MyLabel(QWidget *parent = 0, Qt::WindowFlags f = 0);
 
  protected:
    void paintEvent(QPaintEvent *event);
 
  private:
    QPlainTextEdit *m_doc; //it is hidden, only for storing reason.
};

class MyLabel : public QLabel
{
    Q_OBJECT
  public:
    explicit MyLabel(QWidget *parent = 0, Qt::WindowFlags f = 0);

  protected:
    void paintEvent(QPaintEvent *event);

  private:
    QPlainTextEdit *m_doc; //it is hidden, only for storing reason.
};

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So assume there is some content in the text edit and I do this:

void MyLabel::paintEvent(QPaintEvent *event)
{
  Q_UNUSED(event);
  QPainter p(this);
  m_doc->document()->setPageSize(rect().size());
  m_doc->document()->drawContents(&p, rect());
}

void MyLabel::paintEvent(QPaintEvent *event)
{
  Q_UNUSED(event);
  QPainter p(this);
  m_doc->document()->setPageSize(rect().size());
  m_doc->document()->drawContents(&p, rect());
}

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nothing is shown, but when I have this:

void MyLabel::paintEvent(QPaintEvent *event)
{
  Q_UNUSED(event);
  QPainter p(this);
  QTextDocument *d = m_doc->document()->clone();
  d->setPageSize(rect().size());
  d->drawContents(&p, rect());
  d->deleteLater();
}

void MyLabel::paintEvent(QPaintEvent *event)
{
  Q_UNUSED(event);
  QPainter p(this);
  QTextDocument *d = m_doc->document()->clone();
  d->setPageSize(rect().size());
  d->drawContents(&p, rect());
  d->deleteLater();
}

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everything is painted well. But why I have to clone the document??? That's not very performant... What might be the reason why I am not able to use QPlainTextEdit::document() directly?

Thanks