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-rw-r--r--doc/src/examples/basicgraphicslayouts.qdoc55
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
+
*/ \ No newline at end of file