QDockWidget splitter jumps when QMainWindow Resize

Question

In an old program of mine, I have 2-column QTableWidget inside of a QDockWidget.

Building it in modern times (Qt 5.10) I seem to have to override the table's sizeHint() to get it to be a width besides 100px or something. Which was a bit annoying (didn't need this before--why isn't the table's width via headers the default?)

But with that tweaked, there's now another nuisance: if the user does any moving of the splitter for the dock widget, it will be lost on any window resize. I made a little MCVE to show the effect...here's the startup situation:

Then let's say the user drags the splitter a bit (could be expansion, could be contraction--doesn't matter):

Now they drag the bottom edge of the window down a bit, and snap, it jumps back to the preferred size (the sudden jump occurs right when the mouse first starts dragging):

Changing the horizontal size policy from QSizePolicy::Preferred to QSizePolicy::Ignored doesn't seem to influence this behavior, not calling setStretchLastSection() doesn't seem to help either.

I'd prefer if the window be resized vertically that a horizontal splitter not move at all...and if it's resized horizontally that something more gradual be done than a jump. Any ideas? Qt Creator doesn't seem to have this problem with its watchlist, but I'm not familiar enough with the source to go digging into why.

mainwindow.h:

#include <QMainWindow>

QT_BEGIN_NAMESPACE
class QTextEdit;
class SizedTableWidget;
QT_END_NAMESPACE

class SizedTableWidget;

class MainWindow : public QMainWindow {
    Q_OBJECT

    QTextEdit *textEdit;
    SizedTableWidget *table;

public:
    MainWindow ();
};

mainwindow.cpp:

#include <QtWidgets>

#include "mainwindow.h"

class SizedTableWidget : public QTableWidget {
public:
    SizedTableWidget (int rows, int columns, QWidget *parent) :
        QTableWidget (rows, columns, parent) {}

    QSize sizeHint() const {
        return QSize (
            verticalHeader()->width()
                + horizontalHeader()->length()
                + frameWidth() * 2,
            horizontalHeader()->height()
                + verticalHeader()->length()
                + frameWidth() * 2
        );
    }
};

MainWindow::MainWindow() : textEdit(new QTextEdit) {
    setCentralWidget(textEdit);

    QDockWidget *dock = new QDockWidget(tr("Table"), this);
    dock->setAllowedAreas(Qt::LeftDockWidgetArea | Qt::RightDockWidgetArea);

    table = new SizedTableWidget (1 /* rows */, 2 /* cols */, dock);
    table->setHorizontalHeaderLabels(QStringList() << "name" << "value");

    QTableWidgetItem *nameItem = new QTableWidgetItem;
    nameItem->setText("foo");
    table->setItem(0, 0, nameItem);

    QTableWidgetItem *valueItem = new QTableWidgetItem;
    valueItem->setText("10");
    table->setItem(0, 1, valueItem);

    table->horizontalHeader()->setStretchLastSection(true);
    table->setSizePolicy(QSizePolicy::Preferred, QSizePolicy::Expanding);

    dock->setWidget(table);
    addDockWidget(Qt::RightDockWidgetArea, dock);
}

P.S. if anyone knows why the column and row headers on Windows don't have any styling on them, I'd be interested to know...is this on purpose? Looks fine on Linux.

System information:

• Qt 5.10.0
• Qt Creator 4.5.0
• Windows 10 Home, 1709 (Build 16299.125) and MSVC 2017
• Kubuntu Linux 17.10 and gcc 7.2.0

Answer 1

This appears to be a bug--now confirmed by multiple parties--that appeared in Qt 5.10:

https://bugreports.qt.io/browse/QTBUG-65592

A proposed workaround until it is fixed is given in the comments:

Calling resizeDocks({nameOfAnyDock}, {40}, Qt::Horizontal) enabled the resize to work (the exact number is irrelevant). The function is called immediately after calling addDockWidget.