Qt5 QDockWidget with Fixed Height CentralWidget - c++

Question

I'm trying to use dock widgets on the main window class in Qt5. However, when I set the central widget to have a fixed height Qt has trouble docking the windows to the top or bottom. Basically, it looks like there is some "padding" or "margins" above and below the central widget. If I set an auto height on the widget, the docking works fine all they way edge-to-edge (top/bottom). How can I either remove the margins or enable the docking function while using a fixed height central widget?
See screenshots for example.
Dock Right w/ Auto Height (No Margins on Central Widget)
Dock Bottom w/ Auto Height (No Margins on Central Widget)
Dock Bottom w/ Fixed Height (Margins/Padding--Grey areas, won't dock)
Here is the code if that helps.
Header:
class MainWindow : public QMainWindow {
Q_OBJECT
public:
MainWindow(QString);
~MainWindow();
private:
void createDockWindows();
QListWidget *m_dock_list;
QString m_directory;
QWidget *m_mainWidget;
};
Class definition:
MainWindow::MainWindow(QString program)
: m_directory(".")
{
m_mainWidget = new QWidget;
m_mainWidget->setFixedHeight(156);
m_mainWidget->setStyleSheet("background-color: blue;");
createDockWindows();
// set central widget and default size
setCentralWidget(m_mainWidget);
}
// dock functions
void MainWindow::createDockWindows()
{
QDockWidget *dock = new QDockWidget(tr("Dock List"), this);
dock->setAllowedAreas(Qt::LeftDockWidgetArea |
Qt::RightDockWidgetArea |
Qt::BottomDockWidgetArea);
m_dock_list = new QListWidget(dock);
m_dock_list->addItems(QStringList()
<< "item 1"
<< "item 2"
<< "item 3"
<< "item 4");
dock->setWidget(m_dock_list);
addDockWidget(Qt::RightDockWidgetArea, dock);
}

Answer 1

In case anyone else tries to figure out this behavior, here is what I've found. The top and bottom margins are just Qt trying to place the fixed size widget into a space larger than the widget (obvious). However, the restricted docking ability results from the docking widget having a minimum vertical size. Thus, when window height < central widget height + min(docking widget height) Qt does not allow the dock function. Once the threshold window height is reached (by user resize) then Qt allows the dock function.
I would prefer if the docking feature occurred regardless of window height with an automatic window resize to accommodate the docking window.
Solution using signals
Arguably a bit hacky, and may be hard to maintain if you have a complex layout. But for my use case, this is workable.
Don't enforce the size on the center widget, let it auto-fill the main window.
When the dock changes location it emits the dockLocationChanged. We can auto-size the main window if the dockable window is moved into target location. For my case this is the bottom.
Code:
void MainWindow::createDockWindows()
{
...
QObject::connect(dock, SIGNAL(dockLocationChanged(Qt::DockWidgetArea)),
this, SLOT(s_dock_window_resize(Qt::DockWidgetArea)));
}
// Autosize window slot on dock location change.
void MainWindow::s_dock_window_resize(Qt::DockWidgetArea area)
{
if (area == Qt::DockWidgetArea::BottomDockWidgetArea) {
// m_mainWidget_min_height is the height we would have enforced
// on the widget. Now we set it somewhere else and check it here.
int min_height = m_dock_list->height() + m_mainWidget_min_height;
if (min_height > MainWindow::height()) {
MainWindow::resize(MainWindow::width(), min_height);
}
}
}