How to show a QDialog in center of a QGraphicsView? - qt

Question

I have a QGraphicsView subclass where, on context menu on an item, I want to show a Properties dialog.
I would like the dialog to be centered in the view...
As I have it now, with no parent, it is shown in the center of the screen.
MyView::MyView(QWidget *parent) : QGraphicsView(parent) {}
void MyView::showProperties()
{
TabDialog *tabDialog = new TabDialog(); // shows in center of screen
// TabDialog *tabDialog = new TabDialog(this); // doesn't show at all
// TabDialog *tabDialog = new TabDialog((QWidget*)this->parent()); // doesn't show at all
tabDialog->setWindowFlags(Qt::WindowCloseButtonHint | Qt::WindowSystemMenuHint);
tabDialog->exec();
delete tabDialog;
}
The view is placed in a groupbox... so the parent is the groupbox...
How can I call the dialog using a parent ?

Answer 1

You have to set the dialog to be a top-level window, not simply a child widget that would be embedded in your view. Your setWindowsFlags call resets the relevant flags from the dialog. You need to manually preserve them.
You also should never use exec() to reenter the event loop since this requires that a lot of your other code needs to be reentrant as well.
A minimal fix would look like:
void MyView::showProperties()
{
auto dialog = new TabDialog(this);
dialog->setWindowFlags(Qt::Dialog |
Qt::WindowCloseButtonHint |
Qt::WindowSystemMenuHint);
dialog->setAttribute(Qt::WA_DeleteOnClose);
dialog->show();
}
Perhaps you'd want to cache the dialog:
class MyView : public ... {
QPointer<TabDialog> m_tabDialog; // nulls itself when the dialog perishes
QTimer m_tabDialogTimer;
...
};
MyView::MyView(...) {
m_tabDialogTimer->setSingleShot(true);
...
}
void MyView::showProperties() {
if (! m_tabDialog) {
m_tabDialog = new TabDialog(this);
m_tabDialog->setWindowFlags(Qt::Dialog |
Qt::WindowCloseButtonHint |
Qt::WindowSystemMenuHint);
QObject::connect(&m_tabDialogTimer, &QTimer::timeout,
m_tabDialog, &QObject::deleteLater);
QObject::connect(m_tabDialog, &QDialog::finished, [&this](int){
// the dialog gets deleted 120 seconds after last use
m_tabDialogTimer.start(120);
});
}
m_tabDialogTimer.stop(); // reset pending timeout, if any
m_tabDialog->show();
}