Qt Tutorial - Chapter 3

# Chapter 3: Family Values

This example shows how to create mother and child widgets.

We'll keep it simple and use just a single mother (uh, family values?) and a lone child.

    /****************************************************************
    **
    ** Qt tutorial 3
    **
    ****************************************************************/

    #include <qapplication.h>
    #include <qpushbutton.h>
    #include <qfont.h>

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

        QWidget w;
        w.resize( 200, 120 );

        QPushButton quit( "Quit", &w );
        quit.move( 62, 40 );
        quit.resize( 75, 30 );
        quit.setFont( QFont( "Times", 18, QFont::Bold ) );

        QObject::connect( &quit, SIGNAL(clicked()), &a, SLOT(quit()) );

        a.setMainWidget( &w );
        w.show();
        return a.exec();
    }

## Line by Line Walk-Through

            QWidget w;

Here we simply create a widget. Note that we did not have to include `qwidget.h,` because we have included qpushbutton.h and QPushButton is a subclass of QWidget (see Class Hierarchy).

A QWidget does not handle any events, it simply displays itself using its background color and caption.

            w.resize( 200, 120 );

We set the width to 200 pixels and the height to 120 pixels.

            QPushButton quit( "Quit", &w );

A child is born.

This QPushButton is created with both a text, "Quit", and a mother, w. A child widget is always on top of its mother. When displayed, it is clipped by its mother's bounds.

            quit.move( 62, 40 );

The child is moved to a position of 62,40, relative to its mother's top left corner (excluding the window frame). The coordinate is as usual for a visual display, x increases to the right and y increases downwards.

            w.show();

When a widget is shown, it will call show for all its children (except those you have done an explicit hide() on).

## Behavior

Note that if you resize the widget, the button is not resized, unlike the programs in the first two chapters. That's because the top level widget is a QWidget, which does not react to resizing.

If you're using X11, you will see the same effect if you invoke the program with -geometry.

## Excercises

Try changing the arguments to quit.move() and/or quit.resize(). What happens if quit is partly "outside" w?

For X11 users:

Also try moving the w.resize() to after the quit.move/resize, and to after a.setMainWidget(). Does -geometry still work?

You may now go on to chapter four.

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