diff options
Diffstat (limited to 'doc/src/examples/flowlayout.qdoc')
| -rw-r--r-- | doc/src/examples/flowlayout.qdoc | 115 |
1 files changed, 112 insertions, 3 deletions
diff --git a/doc/src/examples/flowlayout.qdoc b/doc/src/examples/flowlayout.qdoc index 557ba39..3e7ec22 100644 --- a/doc/src/examples/flowlayout.qdoc +++ b/doc/src/examples/flowlayout.qdoc @@ -43,8 +43,117 @@ \example layouts/flowlayout \title Flow Layout Example - The Flow Layout example demonstrates a custom layout that arranges child widgets from - left to right and top to bottom in a top-level widget. + The Flow Layout example demonstrates a custom layout that arranges child + widgets from left to right and top to bottom in a top-level widget. + + \image flowlayout-example.png Screenshot of the Flow Layout example + + The items are first laid out horizontally and then vertically when each line + in the layout runs out of space. + + The Flowlayout class mainly uses QLayout and QWidgetItem, while the + Window uses QWidget and QLabel. 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. - \image flowlayout-example.png */ |