How to clear ExtraSelections in QPlainTextEdit

Question

Sorry if this is a newbie question. I have some code for marking errors in an editor and I can't find how to clear the markings when the errors are gone. Here's the method I'm calling for rendering the errors.

void Editor::highlightErrors( Thing* t )
{
    if ( !t )
        return; 

    const std::vector<Thing::Error>& errors = t->errors();

    QTextCursor tc = textCursor();
    tc.select(QTextCursor::Document);

    QList<QTextEdit::ExtraSelection> extraSelections;
    for(int i = 0; i < errors.size(); ++i) {
        const Thing::Error& error = errors[i];
        QTextEdit::ExtraSelection sel;
        sel.format = this->errorFormat();
        sel.format.setToolTip(QString(error.error.c_str()));
        sel.cursor = tc;
        sel.cursor.clearSelection();
        sel.cursor.setPosition(error.startPos);
        sel.cursor.movePosition(QTextCursor::NextCharacter, QTextCursor::KeepAnchor, error.endPos - error.startPos);
        sel.cursor.mergeCharFormat(sel.format);
        extraSelections.append(sel);
    }
    setExtraSelections(extraSelections);
}

I would expect QPlainTextEdit to redraw the text without the error format, when this method is called with no errors, but it doesn't. QTextLayout::draw is properly called and the extra selections are cleared as well but the text is still being drawn with the error format.

Thanks for the help.

score 2 · Answer 1 · answered Apr 22 '13 at 14:14

Seems more like a Qt bug to me.

If your just looking for a fix / workaround:

Add this after tc.select(QTextCursor::Document);:

  tc.setCharFormat(textCursor().charFormat());

That should sort the issue out.

Details:

This is the function I was testing this with. I just made the function take an int num and format those char positions as an extraSelection with custom format(Does not include fix I mentioned above).

void MainWindow::highlightErrors(int num) {
  QTextCursor tc = ui_.textEdit->textCursor();
  tc.select(QTextCursor::Document);
  QTextCharFormat format;
  QColor lineColor = QColor(Qt::red);
  format.setBackground(lineColor);
  // format.setFontCapitalization(QFont::AllLowercase);
  QList<QTextEdit::ExtraSelection> extraSelections;
  for(int i = 0; i < num; ++i) {
    QTextEdit::ExtraSelection selection;
    selection.format = format;
    selection.format.setToolTip(QString::number(i));
    selection.cursor = tc;
    selection.cursor.clearSelection();
    selection.cursor.setPosition(i);
    selection.cursor.movePosition(QTextCursor::NextCharacter, QTextCursor::KeepAnchor, 1);
    // selection.cursor.mergeCharFormat(selection.format);
    extraSelections.append(selection);
  }
  ui_.textEdit->setExtraSelections(extraSelections);
}

In the above code 2 lines are commented. All that happens is a red background gets applied. Now this works fine.

However if we uncomment format.setFontCapitalization(QFont::AllLowercase);, and re-run we can see the background work as expected but the lowercase change does not get applied(make sure it's caps to begin-with) (This is what I reckon is the Qt bug since format changes only apply partially)

Now if we also uncomment selection.cursor.mergeCharFormat(selection.format);, we can see the lowercase format is applied as well but the format removal stops working.

Hence us needing a fix to reset the CharFormat() on entire document when errorSelection() is changed.

How to clear ExtraSelections in QPlainTextEdit

1 Answers1