Layout Classes

If you need more control over the layout, use a QLayout subclass. The layout classes included in Qt are QGridLayout and QBoxLayout. (QHBoxLayout and QVBoxLayout are trivial subclasses of QBoxLayout, that are simpler to use and make the code easier to read.)

When you use a layout, you must insert each child both into its parent widget (done in the constructor) and into its layout (typically done with a function called addWidget()). This way, you can give layout parameters for each widget, specifying properties like alignment, stretch, and placement.

The following code makes a grid like the one above, with a couple of improvements:

    QWidget *main = new QWidget;

    // make a 1x1 grid; it will auto-expand
    QGridLayout *grid = new QGridLayout( main, 1, 1 );

    // add the first four widgets with (row, column) addressing
    grid->addWidget( new QLabel( "One", main ),   0, 0 );
    grid->addWidget( new QLabel( "Two", main ),   0, 1 );
    grid->addWidget( new QLabel( "Three", main ), 1, 0 );
    grid->addWidget( new QLabel( "Four", main ),  1, 1 );

    // add the last widget on row 2, spanning from column 0 to
    // column 1, and center aligned 
    grid->addMultiCellWidget( new QLabel( "Five", main ), 2, 2, 0, 1,
                              Qt::AlignCenter );

    // let the ratio between the widths of columns 0 and 1 be 2:3
    grid->setColStretch( 0, 2 );
    grid->setColStretch( 1, 3 );

You can insert layouts inside a layout by giving the parent layout as a parameter in the constructor.

    QWidget *main = new QWidget;
    QLineEdit *field = new QLineEdit( main );
    QPushButton *ok = new QPushButton( "OK", main );
    QPushButton *cancel = new QPushButton( "Cancel", main );
    QLabel *label = new QLabel( "Write once, compile everywhere.", main );

    // a layout on a widget
    QVBoxLayout *vbox = new QVBoxLayout( main );
    vbox->addWidget( label );
    vbox->addWidget( field );

    // a layout inside a layout
    QHBoxLayout *buttons = new QHBoxLayout( vbox );
    buttons->addWidget( ok );
    buttons->addWidget( cancel );

Custom Layouts