Nice text formatting in QTextEdit, like Qt Creator does

Question

Qt Creator spots a nice formatting operation, drawing a thin frame around some text (here an example, I refer to the frames around addRow, the yellow areas were the result a text find operation that also had framed the locations found, before I moved the cursor..)

I've been unable to find how to get that effect in QTextEdit. I tried to read from Qt Creator sources, but they are too large for uninformed search...

edit

I started just now to look into custom QTextCharAttribute, via

class framedTextAttr : public QTextObjectInterface {...}

edit

It's working: as per my answer below.

Answer 1

Use QTextEdit::setExtraSelections() to highlight any arbitrary sections of the document. QTextEdit::ExtraSelection class is simple class with public member variables, used to define each highlight. To create a highlight,

1. get QTextCursor from the QTextEdit
2. manipulate the cursor so that it contains the right text as selection
3. store cursor and desired QTextCharFormat in an ExtraSelections object (just assign values, no need for pointers or new)
4. store the ExtraSelections object (as value) in QList
5. repeat above for all highlights you want
6. call the setExtraSelections() method

Some example code:

#include <QtGui>

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);

    // create QTextEdit, with lot of text in it
    QTextEdit w("Alice and Bob (and Eve). ");
    for(int i=0;i<10;++i) w.setText(w.toPlainText() + w.toPlainText());

    // prepare variables for highlights
    QTextCharFormat fmt;
    fmt.setUnderlineStyle(QTextCharFormat::SingleUnderline);
    fmt.setUnderlineColor(QColor(200,200,200));
    fmt.setBackground(QBrush(QColor(230,230,230)));

    // highlight all text in parenthesis
    QTextCursor cursor = w.textCursor();
    while( !(cursor = w.document()->find(QRegExp("\\([^)]*\\)"), cursor)).isNull()) {
        QTextEdit::ExtraSelection sel = { cursor, fmt };
        selections.append(sel);
    }

    // set, show, go!
    w.setExtraSelections(selections);
    w.show();
    return a.exec();
}