QDialog default layout is NULL

kevin009

Hello,

I'm creating a dialog derived from QDialog. I'm designing it in the Qt Creator designer. I specified, in the designer, a vertical layout for my widgets. Everything works and looks fine. However, I'm trying to prevent the resizing of my dialog. After some research I saw that I could do this with QWidget::setFixedSize() and I could pass QWidget::sizeHint() as a parameter. The problem is that size hint returns a QSize of {-1, -1}. After looking at the source code it appears sizeHint returns this if no layout is assigned to the QDialog i.e. d->layout == nullptr. I thought that assigning a layout in the designer would set the d->layout member in QWidget. Apparently I was wrong.
My question is, how can I get a valid sizeHint without programatically setting the layout of my QDialog?

Thank you,
Kevin

ChrisW67

@kevin009 If the QDialog has a vertical layout applied to it then QWidget::layout() will return a non-null value. If the layout contains child widgets then you will get a valid QWidget::sizeHint(). A default Dialog project started with Creator, with a vertical layout and text edit placed in the dialog:

#include "widget.h"
#include <QDebug>
#include <QApplication>

int main(int argc, char *argv[]) {
    QApplication a(argc, argv);
    Widget w;
    qDebug() << "Layout" << w.layout() << w.sizeHint();
    w.show();
    return a.exec();
}

Layout 0x55baa5b16560 QSize(278, 214)

Note that applying a vertical layout to the dialog:

is not the same thing as dropping vertical layout in the dialog's client area.

Doing this, leads to the result you describe.

kevin009

@ChrisW67 Thanks for replying. I was doing as you suggested but still getting the behaviour I specified. Turns out I had a conflicting ui generated header file that had the manually added layout which explains why I was experiencing a NULL layout. Once I deleted the conflicting file everything worked as expected.
Thanks for the extremely easy to follow instructions.

Kevin