Preserving/Restoring QDockWidget size

Axel Spoerl

@Perdrix
Hi David,
making sure we're on the same page.
The workflow is:

application starts with a docked dock widget.
dock widget is unplugged programmatically by setFloating(true).
dock widget is resized, either manually or programmatically.
application is closed, state and geometry are saved.
application is started again, state and geometry are restored.
problem: dock widget bounces back to default geometry.

Cheers
Axel

Axel Spoerl

@Axel-Spoerl
Ok, I must apologize, you have found a bug, a missing feature, whatever you wanna call it.

If I understand you correctly, the issue is the undocked geometry.
It is held by QDockWidgetPrivate::undockedGeometryand unfortunately not saved anywhere.
I'll look into a fix. It is, however, not an easy patch. QWidget::saveGeometry() is not virtual, so the straight forward approach of overriding it in QDockWidgetwon't fly. The undocked geometry is held in the private header, without public accessors, so a stright forward workaround won't fly either.

The fix will probably be a version bump of QDockAreaLayout::saveState(). But that'll kick be available in the next release of 6.5 at the earliest.
The workaround is a bit of plumbing. When the application closes, all dock widgets need to be made floating, after the main window state was saved. Then their undocked geometry becomes available in geometry()and needs to be saved as well. I'll be back with a suggestion.

Perdrix

@Axel-Spoerl Nope this is the DOCKED size.

So work flow is:

Open application
Adjust vertical height of lower dock widget
Close application
Reopen application. Size lower dock widget is same as if lower dock widget hadn't been resized.

Axel Spoerl

@Perdrix
Hi David,

so we're not talking about undocked dock widgets' geometry?
In that case, you're not affected by the bug, that the undocked geometry is not saved.

I have the feeling that something is wrong in the application code.

Just tried to demonstrate the problem in a simple reproducer. But there is no problem, it works perfectly

mainwindow.h

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>
#include <QDockWidget>

QT_BEGIN_NAMESPACE
namespace Ui { class MainWindow; }
QT_END_NAMESPACE

class MainWindow : public QMainWindow
{
    Q_OBJECT

public:
    MainWindow(QWidget *parent = nullptr);
    ~MainWindow();

private:
    void readSettings();
    void writeSettings() const;
    Ui::MainWindow *ui;
};
#endif // MAINWINDOW_H

mainwindow.cpp

#include "mainwindow.h"
#include "./ui_mainwindow.h"
#include <QSettings>

MainWindow::MainWindow(QWidget *parent)
    : QMainWindow(parent)
    , ui(new Ui::MainWindow)
{
    ui->setupUi(this);

    for (int i = 0; i < 4; ++i) {
        const QString name = "DockWidget-" + QString::number(i);
        QDockWidget *dw = new QDockWidget(name, this);
        dw->setObjectName(name);
        addDockWidget(static_cast<Qt::DockWidgetArea>(i << 2), dw);
    }
    readSettings();
}

MainWindow::~MainWindow()
{
    writeSettings();
    delete ui;
}

void MainWindow::readSettings()
{
    const QSettings s("Test", "DockWidgetGeometry");
    if (!s.contains("MainWindowState"))
        return;

    const QByteArray array = s.value("MainWindowState").toByteArray();
    restoreState(array);
}

void MainWindow::writeSettings() const
{
    QSettings s("Test", "DockWidgetGeometry");
    s.setValue("MainWindowState", saveState());
}

main.cpp

#include "mainwindow.h"

#include <QApplication>

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    MainWindow w;
    w.show();
    return a.exec();
}

I start the application, move all dock widgets to the left dock, join two as floating tabs, change their sizes. Whatever I do is exactly recovered after closing and re-starting the app.

So I suspect that your application touches the docked dockwidgets' size after the state is restored.

Cheers
Axel

Perdrix

@Axel-Spoerl The only code I have the messes with its size is in SetupUi, and that is done before the code that tries to restore its size.

    void setupUi(QDockWidget *PictureList)
    {
        if (PictureList->objectName().isEmpty())
            PictureList->setObjectName("PictureList");
        PictureList->resize(618, 156);
        QSizePolicy sizePolicy(QSizePolicy::Preferred, QSizePolicy::Preferred);
        sizePolicy.setHorizontalStretch(0);
        sizePolicy.setVerticalStretch(0);
        sizePolicy.setHeightForWidth(PictureList->sizePolicy().hasHeightForWidth());
        PictureList->setSizePolicy(sizePolicy);
        PictureList->setMinimumSize(QSize(618, 156));
        PictureList->setStyleSheet(QString::fromUtf8(""));
        PictureList->setFeatures(QDockWidget::DockWidgetFloatable|QDockWidget::DockWidgetMovable);
        PictureList->setAllowedAreas(Qt::BottomDockWidgetArea|Qt::RightDockWidgetArea);
        PictureList->setWindowTitle(QString::fromUtf8("Light Frames: 0      -      Dark Frames: 0      -      Flat Frames: 0      -   Dark Flat Frames: 0   -      Offset/Bias Frames: 0"));
        dockWidgetContents = new QWidget();
        dockWidgetContents->setObjectName("dockWidgetContents");
        QSizePolicy sizePolicy1(QSizePolicy::Expanding, QSizePolicy::Expanding);
        sizePolicy1.setHorizontalStretch(0);
        sizePolicy1.setVerticalStretch(0);
        sizePolicy1.setHeightForWidth(dockWidgetContents->sizePolicy().hasHeightForWidth());
        dockWidgetContents->setSizePolicy(sizePolicy1);
        verticalLayout = new QVBoxLayout(dockWidgetContents);
        verticalLayout->setObjectName("verticalLayout");
        tableView = new QTableView(dockWidgetContents);
        tableView->setObjectName("tableView");

        verticalLayout->addWidget(tableView);

        tabBar = new QTabBar(dockWidgetContents);
        tabBar->setObjectName("tabBar");
        QSizePolicy sizePolicy2(QSizePolicy::Expanding, QSizePolicy::Minimum);
        sizePolicy2.setHorizontalStretch(0);
        sizePolicy2.setVerticalStretch(0);
        sizePolicy2.setHeightForWidth(tabBar->sizePolicy().hasHeightForWidth());
        tabBar->setSizePolicy(sizePolicy2);
        tabBar->setMinimumSize(QSize(0, 28));
        tabBar->setMaximumSize(QSize(16777215, 28));

        verticalLayout->addWidget(tabBar);

        PictureList->setWidget(dockWidgetContents);

        retranslateUi(PictureList);

        QMetaObject::connectSlotsByName(PictureList);
    } // setupUi

What's more is that if the QSettings values for geometry and windowState aren't present, the only code that I have to adjust the size is at the start of the code I posted earlier where it does

resizeDocks({ pictureList }, { 150 }, Qt::Vertical);

and that appears to set the size just fine for the FIRST time open:

Subsequent opens always open to a large size that appears related to the main window size.

Perdrix

@Perdrix Maybe I am trying to restore the geometry and window state at the wrong time? I am doing it in code invoked from showEvent()

void DeepSkyStacker::showEvent(QShowEvent* event)
{
	if (!event->spontaneous())
	{
		if (!initialised)
		{
			initialised = true;
			onInitialise();
		}
	}
	// Invoke base class showEvent()
	return Inherited::showEvent(event);
}

Axel Spoerl

@Perdrix
Hi David,
If I tweak the reproducer and override QMainWindow::showEvent(QShowEvent *event), it works as well.

I don't know about the DeepSkyStacker class, where it inherits from and when its first non-spontaneuous show event is consumed. My gut feeling tells me to put some pocket money on the show event. It's an unusual place to call QMainWindow::restoreState(): Are the dock widgets are already constructed and added to the main window, when the show event is consumed? The dock widget part of the call will be a no-op, if the dock widgets aren't in place or don't have an object name.

I'd happily look into the code of DSS, because it's a great piece of software (have I ever mentioned that? Apologies if I haven't). It's a VS project, however, and I only use Qt Creator.

I'd try the following:

play with the reproducer in my earlier post, to see if the issue can be isolated
play with the dock widgets: Tab them, undock them, close and restart the app => see if anything is restored at all.
move the the code calling QMainWindow::restoreState() right after the construction of the dock widgets.

Cheers
Axel

Perdrix

@Axel-Spoerl The widgets are also constructed in onInitialise().

You suggest that showEvent() is an unusual place from which to call restoreState(). Where would you normally put it? At the end of the ctor as you did in you small example?

Axel Spoerl

@Perdrix said in Preserving/Restoring QDockWidget size:

At the end of the ctor as you did in you small example?

The c'tor is definitely a good spot, but it has to be called after the dock widgets are fully created.

Perdrix

@Axel-Spoerl Moved the code to the ctor and all now works!

The final code now reads:

	ZTRACE_RUNTIME("Restoring Window State and Position");
	QSettings settings{};
	settings.beginGroup("MainWindow");

	if (settings.contains("geometry") && settings.contains("maximised"))
	{
		const QByteArray geometry{ settings.value("geometry").toByteArray() };
		const bool maximised{ settings.value("maximised").toBool() };

		if (maximised)
		{
			showMaximized();
			setGeometry(screen()->availableGeometry());
		}
		else
		{
			restoreGeometry(geometry);
		}
	}

	if (settings.contains("windowState"))
	{
		auto windowState{ settings.value("windowState").toByteArray() };

		restoreState(windowState);
	}

	settings.endGroup();

Thanks
David

Axel Spoerl

@Perdrix
Hey David! Great! Glad that it works!
Just two minor nitpicks:

no need to instantiate settings with curly braces.
if the settings object is meant to be only for reading settings, I would constify it. I've had strange bugs where settings became automagically written. E.g. in your case, an empty "MainWindow" group would be created. Such things are hard to debug, hence my constification paranoia.

Perdrix

@Axel-Spoerl Thanks for all the help.

If I made the settings object const, I suspect I couldn't issue settings.beginGroup()? Or does that change a mutable member of the class?

Axel Spoerl

@Perdrix
Good point, you are right. beginGroup()isn't const. So my advice is bad. Apologies, I'll take it back.

JonB

@Axel-Spoerl
There is something wrong (lacking) in QSettings if the only reason a non-const can't be used to read is that you are forced to use beginGroup().

Can one make a key to pass to value() to bypass the need to beginGroup()?

Axel Spoerl

@JonB
Fully agree. QSettings deserves some love for sure.

Perdrix

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Preserving/Restoring QDockWidget size