QSplitter does not correctly set sizes

Question

I have a horizontal QSplitter with two widgets. I want to replace the right hand widget with a new one in a way that the proportions the user has set are maintained. Below is a simplified version of the code I currently have:

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

    splitter = new QSplitter(this);
    splitter->setOrientation(Qt::Horizontal);

    leftWidget = new QPushButton("left", splitter);
    rightWidget = new QPushButton("right", splitter);

    splitter->addWidget(leftWidget);
    splitter->addWidget(rightWidget);

    setCentralWidget(splitter);
}

void MainWindow::swapLayout()
{
    QList<int> sizes = splitter->sizes();

    rightWidget->deleteLater();
    splitter->update();

    rightWidget = new QPushButton("new right", splitter);

    splitter->addWidget(rightWidget);
    splitter->setSizes(sizes);
}

swapLayout() saves the sizes, removes the right widget, adds a new right hand widget and attempts to reset the sizes. However the left hand widget occupies 100% of the space. Without trying to restore the sizes the widgets both take up 50% of the space.

Answer 1

I think the actual order of operations is:

1. saving sizes of 2 widgets;
2. adding 3rd widget.
3. setting size for 3 widgets (and sizes.at(2) is 0 by default.
4. Deleting 2nd widget.

It caused by the fact that deleteLater() only schedules deleting, and actual deleting is processed after you exit swapLayout() method. Try delete rightWidget; instead of rightWidget->deleteLater(); if it possible. Or process events between deleting rightWidget and adding new one.