Remove QTextFrame from QTextDocument

[SGaist]

Hi and welcome to devnet,

IIRC, calling delete on the QTextFrame object should remove it from the document.

[wolpers]

@SGaist I think you are correct. I followed your hint and finally found a note in the QTextFrame's destructor documentation: Destroys the frame, and removes it from the document's layout.

Unfortunately this causes the application to crash with a segmentation fault, but I am still looking into this.

Thanks for your help!

[SGaist]

You're welcome !

What does the debugger say ?

[wolpers]

@SGaist

I called myframe->deleteLater() within a method overriding virtual void QTextEdit::keyPressEvent(QKeyEvent *e)

Calling delete myframe has the same effect.

Here is the call stack NetBeans provides me with:

QMetaObject::cast(QObject*) const ()
QTextFrame::iterator::operator++() ()
?? ()
?? ()
QTextDocumentLayout::draw(QPainter*, QAbstractTextDocumentLayout::PaintContext const&) ()
QWidgetTextControl::drawContents(QPainter*, QRectF const&, QWidget*) ()
?? ()
QTextEdit::paintEvent(QPaintEvent*) ()
QWidget::event(QEvent*) ()
QFrame::event(QEvent*) ()
QCoreApplicationPrivate::sendThroughObjectEventFilters(QObject*, QEvent*) ()
QApplicationPrivate::notify_helper(QObject*, QEvent*) ()
QApplication::notify(QObject*, QEvent*) ()
QCoreApplication::notifyInternal2(QObject*, QEvent*) ()
QWidgetPrivate::sendPaintEvent(QRegion const&) ()
QWidgetPrivate::drawWidget(QPaintDevice*, QRegion const&, QPoint const&, int, QPainter*, QWidgetBackingStore*) ()
?? ()
?? ()
QWidgetPrivate::syncBackingStore() ()
QWidget::event(QEvent*) ()
QMainWindow::event(QEvent*) ()
QApplicationPrivate::notify_helper(QObject*, QEvent*) ()
QApplication::notify(QObject*, QEvent*) ()
QCoreApplication::notifyInternal2(QObject*, QEvent*) ()
QCoreApplicationPrivate::sendPostedEvents(QObject*, int, QThreadData*) ()
?? ()
g_main_context_dispatch ()
?? ()
g_main_context_iteration ()
QEventDispatcherGlib::processEvents(QFlagsQEventLoop::ProcessEventsFlag) ()
QEventLoop::exec(QFlagsQEventLoop::ProcessEventsFlag) ()
QCoreApplication::exec() ()
main (argc=1, argv=0x7fffffffe658)

[wolpers]

nope, was lying. Calling delete myframe changes the callstack slightly. Still causing segmentation fault, though.

QTextFrame::lastPosition() const ()
?? ()
?? ()
?? ()
?? ()
QTextDocumentLayout::draw(QPainter*, QAbstractTextDocumentLayout::PaintContext const&) ()
QWidgetTextControl::drawContents(QPainter*, QRectF const&, QWidget*) ()
?? ()
QTextEdit::paintEvent(QPaintEvent*) ()
QWidget::event(QEvent*) ()
QFrame::event(QEvent*) ()
QCoreApplicationPrivate::sendThroughObjectEventFilters(QObject*, QEvent*) ()
QApplicationPrivate::notify_helper(QObject*, QEvent*) ()
QApplication::notify(QObject*, QEvent*) ()
QCoreApplication::notifyInternal2(QObject*, QEvent*) ()
QWidgetPrivate::sendPaintEvent(QRegion const&) ()
QWidgetPrivate::drawWidget(QPaintDevice*, QRegion const&, QPoint const&, int, QPainter*, QWidgetBackingStore*) ()
?? ()
?? ()
QWidgetPrivate::syncBackingStore() ()
QWidget::event(QEvent*) ()
QMainWindow::event(QEvent*) ()
QApplicationPrivate::notify_helper(QObject*, QEvent*) ()
QApplication::notify(QObject*, QEvent*) ()
QCoreApplication::notifyInternal2(QObject*, QEvent*) ()
QCoreApplicationPrivate::sendPostedEvents(QObject*, int, QThreadData*) ()
?? ()
g_main_context_dispatch ()
?? ()
g_main_context_iteration ()
QEventDispatcherGlib::processEvents(QFlagsQEventLoop::ProcessEventsFlag) ()
QEventLoop::exec(QFlagsQEventLoop::ProcessEventsFlag) ()
QCoreApplication::exec() ()
main (argc=1, argv=0x7fffffffe658)

[wolpers]

I created a small self contained snippet for anyone to try out. Maybe someone can tell me what I am doing wrong when attempting to remove a QTextFrame. Hit 'x' one or more times to add a frame, hit 'y' to remove one. This is where things crash.

main.cpp

#include <QApplication>
#include <QtCore>
#include <QtGui>
#include <QtWidgets>


namespace {

    class TestEdit : public QTextEdit {
    protected:

        virtual void keyPressEvent(QKeyEvent *e) {

            if (e->key() == Qt::Key_X) {
                
                QTextCursor cursor = this->textCursor();
                QTextFrameFormat frameFormat;
                frameFormat.setBackground(QColor(Qt::red));
                QTextFrame* frame = cursor.insertFrame(frameFormat);
                
            } else if (e->key() == Qt::Key_Y) {
                
                QTextCursor cursor = this->textCursor();
                QTextFrame* currentFrame = cursor.currentFrame();
                if(currentFrame != this->document()->rootFrame()) {
                    //delete currentFrame;
                    currentFrame->deleteLater();
                    return;
                }
                
            }

            QTextEdit::keyPressEvent(e);
        }
    };
}

int main(int argc, char *argv[]) {
    QApplication app(argc, argv);
    QMainWindow* w = new QMainWindow();
    w->setAttribute(Qt::WA_DeleteOnClose);
    w->setCentralWidget(new TestEdit());
    w->adjustSize();
    w->move(QApplication::desktop()->screen()->rect().center() - w->rect().center());
    w->show();
    return app.exec();
}

[SGaist]

I haven't tested it yet but one thing I see is that you don't test that currentFrame is not null

[wolpers]

@SGaist Indeed, I missed that check. I added it in my local copy and debugged it. Unfortunately it does not make a difference. The currentFrame pointer is valid and currentFrame->deleteLater(); is called.

[wolpers]

I created a bugreport for this. Looks to me that at least the documentation could need some work in this area. For the record: I found out that removing all child blocks (and frames?) leads to the automatic removal of the frame itself.

https://bugreports.qt.io/browse/QTBUG-53082

[SGaist]

The documentation has been fixed :)