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We will only document the definition and implementation of \c FlowLayout below. \section1 FlowLayout Class Definition The \c FlowLayout class inherits QLayout. It is a custom layout class that arranges its child widgets horizontally and vertically. \snippet examples/layouts/flowlayout/flowlayout.h 0 We reimplement functions inherited from QLayout. These functions add items to the layout and handle their orientation and geometry. We also declare two private methods, \c doLayout() and \c smartSpacing(). \c doLayout() lays out the layout items, while the \c smartSpacing() function calculates the spacing between them. \section1 FlowLayout Class Implementation We start off by looking at the constructor: \snippet examples/layouts/flowlayout/flowlayout.cpp 1 In the constructor we call \c setContentsMargins() to set the left, top, right and bottom margin. By default, QLayout uses values provided by the current style (see QStyle::PixelMetric). \snippet examples/layouts/flowlayout/flowlayout.cpp 2 In this example we reimplement \c addItem(), which is a pure virtual function. When using \c addItem() the ownership of the layout items is transferred to the layout, and it is therefore the layout's responsibility to delete them. \snippet examples/layouts/flowlayout/flowlayout.cpp 3 \c addItem() is implemented to add items to the layout. \snippet examples/layouts/flowlayout/flowlayout.cpp 4 We implement \c horizontalSpacing() and \c verticalSpacing() to get hold of the spacing between the widgets inside the layout. If the value is less than or equal to 0, this value will be used. If not, \c smartSpacing() will be called to calculate the spacing. \snippet examples/layouts/flowlayout/flowlayout.cpp 5 We then implement \c count() to return the number of items in the layout. To navigate the list of items we use \c itemAt() and takeAt() to remove and return items from the list. If an item is removed, the remaining items will be renumbered. All three functions are pure virtual functions from QLayout. \snippet examples/layouts/flowlayout/flowlayout.cpp 6 \c expandingDirections() returns the \l{Qt::Orientation}s in which the layout can make use of more space than its \c sizeHint(). \snippet examples/layouts/flowlayout/flowlayout.cpp 7 To adjust to widgets of which height is dependent on width, we implement \c heightForWidth(). The function \c hasHeightForWidth() is used to test for this dependency, and \c heightForWidth() passes the width on to \c doLayout() which in turn uses the width as an argument for the layout rect, i.e., the bounds in which the items are laid out. This rect does not include the layout margin(). \snippet examples/layouts/flowlayout/flowlayout.cpp 8 \c setGeometry() is normally used to do the actual layout, i.e., calculate the geometry of the layout's items. In this example, it calls \c doLayout() and passes the layout rect. \c sizeHint() returns the preferred size of the layout and \c minimumSize() returns the minimum size of the layout. \snippet examples/layouts/flowlayout/flowlayout.cpp 9 \c doLayout() handles the layout if \c horizontalSpacing() or \c verticalSpacing() don't return the default value. It uses \c getContentsMargins() to calculate the area available to the layout items. \snippet examples/layouts/flowlayout/flowlayout.cpp 10 It then sets the proper amount of spacing for each widget in the layout, based on the current style. \snippet examples/layouts/flowlayout/flowlayout.cpp 11 The position of each item in the layout is then calculated by adding the items width and the line height to the initial x and y coordinates. This in turn lets us find out whether the next item will fit on the current line or if it must be moved down to the next. We also find the height of the current line based on the widgets height. \snippet examples/layouts/flowlayout/flowlayout.cpp 12 \c smartSpacing() is designed to get the default spacing for either the top-level layouts or the sublayouts. The default spacing for top-level layouts, when the parent is a QWidget, will be determined by querying the style. The default spacing for sublayouts, when the parent is a QLayout, will be determined by querying the spacing of the parent layout. */