Archived:Overriding the minimum size constraint of QLayout

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Qt Quick should be used for all UI development on mobile devices. The approach described in this article (using C++ for the Qt app UI) is deprecated.

Article Metadata

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Tested with

Devices(s): N97, N900

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Compatibility

Platform(s): Symbian
Maemo

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Article

Keywords: QLayout, minimum size constraint

Created: kratsan (07 Oct 2010)

Last edited: hamishwillee (11 Oct 2012)

Overview

Qt layouts default have minimum size constraint set for the containing QWidgets which results layout to have a minimum size. If the UI control containing this layout is resized smaller than this limit, the layout just wont get smaller. In mobile resolutions this often means that the corresponding UI control won't scale small enough and the control will be partially drawn outside of the screen.

By overriding the minimum size constraint we can force the layout to scale the containing widgets as small as needed.

Note: The containing widgets might be scaled smaller than they were meant to be scaled. This can result as degraded look and feel in the used widgets.

Preconditions

• Install Nokia Qt SDK see [1]

Overriding the minimum size restraint

minimumsize.pro

TEMPLATE = app
SOURCES += main.cpp

main.cpp

#include <QApplication>
#include <QWidget>
#include <QPushButton>
#include <QVBoxLayout>
 
int main(int argc, char *argv[])
{
    QApplication app(argc, argv);
    QWidget widget;
 
    QLayout *layout = new QVBoxLayout;
#if defined(Q_OS_SYMBIAN) || defined(Q_WS_MAEMO_5)
    layout->setSizeConstraint(QLayout::SetNoConstraint);
#endif
 
    for(int i=0; i<10; i++) {
        QPushButton *button = new QPushButton(QString("%1").arg(i+1));
        layout->addWidget(button);
    }
 
    widget.setLayout(layout);
 
#ifdef Q_OS_SYMBIAN
    widget.showMaximized();
#else
    widget.show();
#endif
    return app.exec();
}

Postconditions

Code example demonstrated of overriding the minimum size constraint of the given layout to force the widgets smaller than their minimum size.