Undo stack remains empty in Qt - c++

Question

I am trying to undo/redo in multi document interface. I have different entities. Each entity has its own class. I have used UndoGroup but when I unable to push them to undoStack dont know whats's wrong there. Can anyone help me to solve the issue.
cadgraphicscene.cpp
CadGraphicsView::CadGraphicsView()
{
undoStack = new QUndoStack(this);
}
QUndoStack *CadGraphicsView::m_undoStack() const
{
return undoStack;
}
void CadGraphicsView::showUndoStack()
{
undoView = 0;
// shows the undoStack window
if (undoView == 0)
{
undoView = new QUndoView(undoStack);
undoView->setWindowTitle("Undo Stack");
}
undoView->show();
}
mainwindow.cpp
MainWindow::MainWindow(QWidget *parent) : QMainWindow(parent)
{
m_undoGroup = new QUndoGroup(this);
QAction *undoAction = m_undoGroup->createUndoAction(this);
undoAction->setShortcut(QKeySequence::Undo);
QAction *redoAction = m_undoGroup->createRedoAction(this);
redoAction->setShortcut(QKeySequence::Redo);
menuEdit->insertAction(menuEdit->actions().at(1), undoAction);
menuEdit->insertAction(undoAction, redoAction);
menuEdit->addAction(undoAction);
menuEdit->addAction(redoAction);
undoAction->setEnabled(true);
redoAction->setEnabled(true);
}
void MainWindow::updateActions()
{
CadGraphicsView *view = currentDocument();
m_undoGroup->setActiveStack(view == 0 ? 0 : view->m_undoStack());
}
void MainWindow::addDocument(CadGraphicsView *view)
{
m_undoGroup->addStack(view->m_undoStack());
connect(view->m_undoStack(), SIGNAL(indexChanged(int)), this, SLOT(updateActions()));
connect(view->m_undoStack(), SIGNAL(cleanChanged(bool)), this, SLOT(updateActions()));
setCurrentDocument(view);
}
void MainWindow::setCurrentDocument(CadGraphicsView *view)
{
mdiArea->currentSubWindow();
}
CadGraphicsView *MainWindow::currentDocument() const
{
return qobject_cast<CadGraphicsView *>(mdiArea->parentWidget());
}
I am confused with why I am not able to push entities to undoStack. Please help me to solve this issue

Answer 1

I think the problem is in these two functions (see the inline comments):
void MainWindow::setCurrentDocument(CadGraphicsView *view)
{
// The view argument is not used at all. You do not set anything here.
mdiArea->currentSubWindow();
}
CadGraphicsView *MainWindow::currentDocument() const
{
// mdiArea->parentWidget() returns the MainWindow, so this function
// always returns 0.
return qobject_cast<CadGraphicsView *>(mdiArea->parentWidget());
// You should write it as
// return qobject_cast<CadGraphicsView *>(mdiArea->activeSubWindow()->widget());
}