Qt: how to make mainWindow automatically resize when centralwidget is resized?

Question

I would like to have my CentralWidget a certain size. What do I need to do to make my mainWindow resize along it's central widget? here the code that doesn't work:

int main (int argc, char **argv) {
    QApplication app(argc, argv);

    QGLFormat glFormat;
    glFormat.setVersion(4,2);
    glFormat.setProfile( QGLFormat::CompatibilityProfile);

    QGLWidget* render_qglwidget = new MyWidget(glFormat);

    QGLContext* glContext = (QGLContext *) render_qglwidget->context();
    glContext->makeCurrent();


    QMainWindow* mainWindow = new MyMainWindow();
    render_qglwidget->resize(720, 486);
    mainWindow->setSizePolicy(QSizePolicy(QSizePolicy::Expanding,QSizePolicy::Expanding));
    mainWindow->setCentralWidget(render_qglwidget);

    render_qglwidget->resize(720, 486);

    mainWindow->show();

    return app.exec();
}

the window that opens will be very small.

i can set the size of the mainwindow using

 mainWindow->resize(720, 486);

and the centralwidget will also change it's size. but the central widget will be slightly squashed because the toolbar of the mainWindow also lies within those 486 pixels.

How to let the mainWindow resize automatically?

Answer 1

You can reimplement QMainWindow::event() to resize the window automatically whenever the size of the central widget changes:

bool MyMainWindow::event(QEvent *ev) {
    if(ev->type() == QEvent::LayoutRequest) {
        setFixedSize(sizeHint());
    }
    return result = QMainWindow::event(ev);
}

You also have to use setFixedSize() for the central widget instead of just resize(). The latter is almost useless when the widget is placed inside a layout (which is a QMainWindowLayout here).