Problem of highlighting text in QPlainTextEdit

[topfortune]

Hello,

My Qt SDK version 4.7.4

I use QPlainTextEdit::setExtraSelections() to highlight some words in QPlainTextEdit. Following is my code:

int pos = block.position() + p;
 
  QTextEdit::ExtraSelection selection;
  selection.cursor = QTextCursor(ui->plainTextEdit->document());
  selection.cursor.setPosition( pos );
  selection.cursor.setPosition( pos+highlighText.length(), QTextCursor::KeepAnchor );
  selection.format.setBackground( backBrush );
  selection.format.setForeground( textBrush );
  selection.format.setProperty( QTextFormat::OutlinePen, outlinePen );
 
  extraSelections.append( selection );

int pos = block.position() + p;

  QTextEdit::ExtraSelection selection;
  selection.cursor = QTextCursor(ui->plainTextEdit->document());
  selection.cursor.setPosition( pos );
  selection.cursor.setPosition( pos+highlighText.length(), QTextCursor::KeepAnchor );
  selection.format.setBackground( backBrush );
  selection.format.setForeground( textBrush );
  selection.format.setProperty( QTextFormat::OutlinePen, outlinePen );

  extraSelections.append( selection );

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Everything seems Ok. But when I move the caret on the position of highlighted text. The highlighted text is not diaplay ok. Please refer to the screenshot.

2012-4-17 11-27-39.png

---

Added after 4 minutes:

I attached a demo for the problem.

Can anybody help me?

[dennis81]

maybe you can force periodical the paint event. It looks like Qt <-> WinXP problem. I have got a similar problem with QPlaintextEdits on some Windows machines with Qt 4.5.3.

[topfortune]

maybe you can force periodical the paint event. It looks like Qt <-> WinXP problem. I have got a similar problem with QPlaintextEdits on some Windows machines with Qt 4.5.3.

I built and run the demo on Ubuntu. And the problem also exists on Linux. I think it must be a bug of Qt. I really don't want to modify the source code of Qt for the problem.

[topfortune]

Can anybody help me? Please....

[Spitfire]

Hey,

I appreciate your effort to prepare the example, in return (and because I had some spare time) I've got solution for you

It seems in fact to be a bug in Qt, from what I've found the paint event for QPlainTextEdit contains wrong rectangle.

You can fix it yourself without affecting Qt source, here's how:

class FixedQPlainTextEdit : public QPlainTextEdit // I guess the name tells you everything :)
{
public:
    FixedQPlainTextEdit( QWidget* parent = 0 ) : QPlainTextEdit( parent ) {}
 
protected:
    void    paintEvent( QPaintEvent* e )
    {
        QPaintEvent* fixed_event = new QPaintEvent( e->rect().adjusted( -1, -1, 0, 0 ) ); // left and top edge need to be adjusted by -1
        QPlainTextEdit::paintEvent( fixed_event );
        delete fixed_event;
    }
};
 
// below is your example code using the FixedQPlainTextEdit class
MainWindow::MainWindow( QWidget* p )
    :
    QMainWindow( p )
{
    QPlainTextEdit* e = new FixedQPlainTextEdit();
    e->appendPlainText( "#include <QtGui/QApplication>" );
    e->appendPlainText( "#include \"mainwindow.h\"" );
    e->appendPlainText( "" );
    e->appendPlainText( "int main(int argc, char *argv[])" );
    e->appendPlainText( "{" );
    e->appendPlainText( "    QApplication a(argc, argv);" );
    e->appendPlainText( "    MainWindow w;" );
    e->appendPlainText( "    w.show();" );
    e->appendPlainText( "" );
    e->appendPlainText( "    return a.exec();" );
    e->appendPlainText( "}" );
 
    this->setCentralWidget( e );
 
    QList<QTextEdit::ExtraSelection> extraSelections;
 
    QBrush backBrush( Qt::yellow );
    QBrush textBrush( Qt::black );
    QPen outlinePen( Qt::gray, 1 );
    QString highlighText = "QApplication";
 
    for( int i=0; i<e->document()->blockCount(); i++ )
    {
        QTextBlock block = e->document()->findBlockByNumber( i );
        if( block.isValid() )
        {
            QString text = block.text();
            int p;
 
            if( (p=text.indexOf(highlighText)) != -1 )
            {
                int pos = block.position() + p;
 
                QTextEdit::ExtraSelection selection;
                selection.cursor = QTextCursor(e->document());
                selection.cursor.setPosition( pos );
                selection.cursor.setPosition( pos+highlighText.length(), QTextCursor::KeepAnchor );
                selection.format.setBackground( backBrush );
                selection.format.setForeground( textBrush );
                selection.format.setProperty( QTextFormat::OutlinePen, outlinePen );
 
                extraSelections.append( selection );
            }
        }
    }
 
    e->setExtraSelections( extraSelections );
}

class FixedQPlainTextEdit : public QPlainTextEdit // I guess the name tells you everything :)
{
public:
    FixedQPlainTextEdit( QWidget* parent = 0 ) : QPlainTextEdit( parent ) {}

protected:
    void    paintEvent( QPaintEvent* e )
    {
        QPaintEvent* fixed_event = new QPaintEvent( e->rect().adjusted( -1, -1, 0, 0 ) ); // left and top edge need to be adjusted by -1
        QPlainTextEdit::paintEvent( fixed_event );
        delete fixed_event;
    }
};

// below is your example code using the FixedQPlainTextEdit class
MainWindow::MainWindow( QWidget* p )
    :
    QMainWindow( p )
{
    QPlainTextEdit* e = new FixedQPlainTextEdit();
    e->appendPlainText( "#include <QtGui/QApplication>" );
    e->appendPlainText( "#include \"mainwindow.h\"" );
    e->appendPlainText( "" );
    e->appendPlainText( "int main(int argc, char *argv[])" );
    e->appendPlainText( "{" );
    e->appendPlainText( "    QApplication a(argc, argv);" );
    e->appendPlainText( "    MainWindow w;" );
    e->appendPlainText( "    w.show();" );
    e->appendPlainText( "" );
    e->appendPlainText( "    return a.exec();" );
    e->appendPlainText( "}" );

    this->setCentralWidget( e );

    QList<QTextEdit::ExtraSelection> extraSelections;

    QBrush backBrush( Qt::yellow );
    QBrush textBrush( Qt::black );
    QPen outlinePen( Qt::gray, 1 );
    QString highlighText = "QApplication";

    for( int i=0; i<e->document()->blockCount(); i++ )
    {
        QTextBlock block = e->document()->findBlockByNumber( i );
        if( block.isValid() )
        {
            QString text = block.text();
            int p;

            if( (p=text.indexOf(highlighText)) != -1 )
            {
                int pos = block.position() + p;

                QTextEdit::ExtraSelection selection;
                selection.cursor = QTextCursor(e->document());
                selection.cursor.setPosition( pos );
                selection.cursor.setPosition( pos+highlighText.length(), QTextCursor::KeepAnchor );
                selection.format.setBackground( backBrush );
                selection.format.setForeground( textBrush );
                selection.format.setProperty( QTextFormat::OutlinePen, outlinePen );

                extraSelections.append( selection );
            }
        }
    }

    e->setExtraSelections( extraSelections );
}

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Edit:
Btw the issue was also visible if you placed the cursor under the highlighted field.

[topfortune]

Hi Spitfire,

It's perfect! Thank you so much for your solution. Thank you so much!!!