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Diffstat (limited to 'doc/src/examples/basicgraphicslayouts.qdoc')
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1 files changed, 41 insertions, 14 deletions
diff --git a/doc/src/examples/basicgraphicslayouts.qdoc b/doc/src/examples/basicgraphicslayouts.qdoc index 92571af..9696fb6 100644 --- a/doc/src/examples/basicgraphicslayouts.qdoc +++ b/doc/src/examples/basicgraphicslayouts.qdoc @@ -45,6 +45,7 @@ The Basic Graphics Layouts example shows how to use the layout classes in QGraphicsView: QGraphicsLinearLayout and QGraphicsGridLayout. + In addition to that it shows how to write your own custom layout item. \image basicgraphicslayouts-example.png Screenshot of the Basic Layouts Example @@ -115,26 +116,24 @@ \section1 LayoutItem Class Definition - The \c LayoutItem class is a subclass of QGraphicsWidget. It has a - constructor, a destructor, and a reimplementation of the - {QGraphicsItem::paint()}{paint()} function. + The \c LayoutItem class is a subclass of QGraphicsLayoutItem and + QGraphicsItem. It has a constructor, a destructor, and some required + reimplementations. + Since it inherits QGraphicsLayoutItem it must reimplement + {QGraphicsLayoutItem::setGeometry()}{setGeometry()} and + {QGraphicsLayoutItem::sizeHint()}{sizeHint()}. + In addition to that it inherits QGraphicsItem, so it must reimplement + {QGraphicsItem::boundingRect()}{boundingRect()} and + {QGraphicsItem::paint()}{paint()}. \snippet examples/graphicsview/basicgraphicslayouts/layoutitem.h 0 - The \c LayoutItem class also has a private instance of QPixmap, \c pix. - - \note We subclass QGraphicsWidget so that \c LayoutItem objects can - be automatically plugged into a layout, as QGraphicsWidget is a - specialization of QGraphicsLayoutItem. + The \c LayoutItem class also has a private instance of QPixmap, \c m_pix. \section1 LayoutItem Class Implementation - In \c{LayoutItem}'s constructor, \c pix is instantiated and the - \c{QT_original_R.png} image is loaded into it. We set the size of - \c LayoutItem to be slightly larger than the size of the pixmap as we - require some space around it for borders that we will paint later. - Alternatively, you could scale the pixmap to prevent the item from - becoming smaller than the pixmap. + In \c{LayoutItem}'s constructor, \c m_pix is instantiated and the + \c{block.png} image is loaded into it. \snippet examples/graphicsview/basicgraphicslayouts/layoutitem.cpp 0 @@ -148,4 +147,32 @@ \snippet examples/graphicsview/basicgraphicslayouts/layoutitem.cpp 2 + The reimplementation of {QGraphicsItem::boundingRect()}{boundingRect()} + will set the top left corner at (0,0), and the size of it will be + the size of the layout items + {QGraphicsLayoutItem::geometry()}{geometry()}. This is the area that + we paint within. + + \snippet examples/graphicsview/basicgraphicslayouts/layoutitem.cpp 3 + + + The reimplementation of {QGraphicsLayoutItem::setGeometry()}{setGeometry()} + simply calls its baseclass implementation. However, since this will change + the boundingRect we must also call + {QGraphicsItem::prepareGeometryChange()}{prepareGeometryChange()}. + Finally, we move the item according to \c geom.topLeft(). + + \snippet examples/graphicsview/basicgraphicslayouts/layoutitem.cpp 4 + + + Since we don't want the size of the item to be smaller than the pixmap, we + must make sure that we return a size hint that is larger than \c m_pix. + We also add some extra space around for borders that we will paint later. + Alternatively, you could scale the pixmap to prevent the item from + becoming smaller than the pixmap. + The preferred size is the same as the minimum size hint, while we set + maximum to be a large value + + \snippet examples/graphicsview/basicgraphicslayouts/layoutitem.cpp 5 + */
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