QMenuBar's height has suddenly changed - bug?

[LucaDanieli]

I had a QWidget displaying a complex layout containing many widgets.

The code was approximately:

#ifndef Q_OS_MAC
    QMenuBar *newMenu = createMenus();
    outerLayout->addWidget(newMenu);
#endif
 
QHBoxLayout * h_layout = new QHBoxLayout;
h_layout->setContentsMargins(0,0,0,0);
h_layout->setSpacing(0);
h_layout->addWidget(newDocumentsDocklet);
h_layout->addWidget(newEditorsDocklet);
 
outerLayout->addLayout(h_layout);
window->setLayout(outerLayout);

#ifndef Q_OS_MAC
    QMenuBar *newMenu = createMenus();
    outerLayout->addWidget(newMenu);
#endif

QHBoxLayout * h_layout = new QHBoxLayout;
h_layout->setContentsMargins(0,0,0,0);
h_layout->setSpacing(0);
h_layout->addWidget(newDocumentsDocklet);
h_layout->addWidget(newEditorsDocklet);

outerLayout->addLayout(h_layout);
window->setLayout(outerLayout);

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This is the result:

01MCm.png

Unfortunately, when I changed my h_layout from QHBoxLayout to QSplitter, the QMenuBar changed its height. I don't understand if this is a bug, as I thought the the QMenuBar had a specific height.

The new code looks like this:

#ifndef Q_OS_MAC
    QMenuBar *newMenu = createMenus();
    outerLayout->addWidget(newMenu);
#endif
 
QSplitter * h_layout = new QSplitter;
h_layout->setOrientation(Qt::Horizontal);
h_layout->addWidget(newDocumentsDocklet);
h_layout->addWidget(newEditorsDocklet);
 
outerLayout->addWidget(h_layout);
window->setLayout(outerLayout);

#ifndef Q_OS_MAC
    QMenuBar *newMenu = createMenus();
    outerLayout->addWidget(newMenu);
#endif

QSplitter * h_layout = new QSplitter;
h_layout->setOrientation(Qt::Horizontal);
h_layout->addWidget(newDocumentsDocklet);
h_layout->addWidget(newEditorsDocklet);

outerLayout->addWidget(h_layout);
window->setLayout(outerLayout);

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This is the new rendering:

KCU9e.png

Is somebody able to help me understand why this has happened? And a way to solve this?

[d_stranz]

You don't show the code, but I assume "outerLayout" is a QVBoxLayout. What you see is probably due to the layout policy of the VBox. When you add a QWidget and another layout to the VBox, it will expand the layout to fill the space not occupied by the QWidget's preferred size. When you add two QWidget instances to a VBox, it will give them equal height unless you call setStretch() to change the layout ratio.

I'm not really sure why you are manually adding a QMenu and QWidgets to a layout, though. QMainWindow will give a you a menu, and you can set the QMainWindow's centralWidget() to your QSplitter. This will give you exactly the behavior you see in your first case and also behave properly on resize, etc.

[LucaDanieli]

Thank you d_stranz.
You are actually right: "outerLayout" is a QVBoxLayout.
I already have a QMainWindow, but some users would prefer to be able to duplicate the mainWindow into many (ideally infinite) new windows.

For this reason I add a new menu to every additional new window (It would not be a problem for Macintosh, but this is the only way I have found to have it work in Linux).

I have followed your suggestion, and I have rewritten the code as follows, adding the QSplitter to a Layout to have it stretched automatically, but the result is still the same:

QSplitter * central_body = new QSplitter;
    central_body->setOrientation(Qt::Horizontal);
    central_body->addWidget(newDocumentsDocklet);
    central_body->addWidget(newEditorsDocklet);
 
    QVBoxLayout * central_body_layout = new QVBoxLayout;
    central_body_layout->addWidget(central_body);
 
    outerLayout->addLayout(central_body_layout);
    window->setLayout(outerLayout);

QSplitter * central_body = new QSplitter;
    central_body->setOrientation(Qt::Horizontal);
    central_body->addWidget(newDocumentsDocklet);
    central_body->addWidget(newEditorsDocklet);

    QVBoxLayout * central_body_layout = new QVBoxLayout;
    central_body_layout->addWidget(central_body);

    outerLayout->addLayout(central_body_layout);
    window->setLayout(outerLayout);

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[d_stranz]

What you wrote was not what I suggested. I actually didn't suggest anything - I pointed out why there was a difference in behavior between your different implementations. Adding an extra VBox layout inside your existing VBox layout doesn't do anything useful, as you can see.

For a real suggestion, I suggest you remove the extra VBox, and instead change the sizePolicy() of the menu bar to have a vertical size policy of "Fixed".