source: trunk/doc/src/examples/basicgraphicslayouts.qdoc@ 9

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41
42/*!
43 \example graphicsview/basicgraphicslayouts
44 \title Basic Graphics Layouts Example
45
46 The Basic Graphics Layouts example shows how to use the layout classes
47 in QGraphicsView: QGraphicsLinearLayout and QGraphicsGridLayout.
48
49 \image basicgraphicslayouts-example.png Screenshot of the Basic Layouts Example
50
51 \section1 Window Class Definition
52
53 The \c Window class is a subclass of QGraphicsWidget. It has a
54 constructor with a QGraphicsWidget \a parent as its parameter.
55
56 \snippet examples/graphicsview/basicgraphicslayouts/window.h 0
57
58 \section1 Window Class Implementation
59
60 The constructor of \c Window instantiates a QGraphicsLinearLayout object,
61 \c windowLayout, with vertical orientation. We instantiate another
62 QGraphicsLinearLayout object, \c linear, whose parent is \c windowLayout.
63 Next, we create a \c LayoutItem object, \c item and add it to \c linear
64 with the \l{QGraphicsLinearLayout::}{addItem()} function. We also provide
65 \c item with a \l{QGraphicsLinearLayout::setStretchFactor()}
66 {stretchFactor}.
67
68 \snippet examples/graphicsview/basicgraphicslayouts/window.cpp 0
69
70 We repeat the process:
71
72 \list
73 \o create a new \c LayoutItem,
74 \o add the item \c linear, and
75 \o provide a stretch factor.
76 \endlist
77
78 \snippet examples/graphicsview/basicgraphicslayouts/window.cpp 1
79
80 We then add \c linear to \c windowLayout, nesting two
81 QGraphicsLinearLayout objects. Apart from the QGraphicsLinearLayout, we
82 also use a QGraphicsGridLayout object, \c grid, which is a 4x3 grid with
83 some cells spanning to other rows.
84
85 We create seven \c LayoutItem objects and place them into \c grid with
86 the \l{QGraphicsGridLayout::}{addItem()} function as shown in the code
87 snippet below:
88
89 \snippet examples/graphicsview/basicgraphicslayouts/window.cpp 2
90
91 The first item we add to \c grid is placed in the top left cell,
92 spanning four rows. The next two items are placed in the second column,
93 and they span two rows. Each item's \l{QGraphicsWidget::}{maximumHeight()}
94 and \l{QGraphicsWidget::}{minimumHeight()} are set to be equal so that
95 they do not expand vertically. As a result, these items will not
96 fit vertically in their cells. So, we specify that they should be
97 vertically aligned in the center of the cell using Qt::AlignVCenter.
98
99 Finally, \c grid itself is added to \c windowLayout. Unlike
100 QGridLayout::addItem(), QGraphicsGridLayout::addItem() requires a row
101 and a column for its argument, specifying which cell the item should be
102 positioned in. Also, if the \c rowSpan and \c columnSpan arguments
103 are omitted, they will default to 1.
104
105 Note that we do not specify a parent for each \c LayoutItem that we
106 construct, as all these items will be added to \c windowLayout. When we
107 add an item to a layout, it will be automatically reparented to the widget
108 on which the layout is installed.
109
110 \snippet examples/graphicsview/basicgraphicslayouts/window.cpp 3
111
112 Now that we have set up \c grid and added it to \c windowLayout, we
113 install \c windowLayout onto the window object using
114 QGraphicsWidget::setLayout() and we set the window title.
115
116 \section1 LayoutItem Class Definition
117
118 The \c LayoutItem class is a subclass of QGraphicsWidget. It has a
119 constructor, a destructor, and a reimplementation of the
120 {QGraphicsItem::paint()}{paint()} function.
121
122 \snippet examples/graphicsview/basicgraphicslayouts/layoutitem.h 0
123
124 The \c LayoutItem class also has a private instance of QPixmap, \c pix.
125
126 \note We subclass QGraphicsWidget so that \c LayoutItem objects can
127 be automatically plugged into a layout, as QGraphicsWidget is a
128 specialization of QGraphicsLayoutItem.
129
130 \section1 LayoutItem Class Implementation
131
132 In \c{LayoutItem}'s constructor, \c pix is instantiated and the
133 \c{QT_original_R.png} image is loaded into it. We set the size of
134 \c LayoutItem to be slightly larger than the size of the pixmap as we
135 require some space around it for borders that we will paint later.
136 Alternatively, you could scale the pixmap to prevent the item from
137 becoming smaller than the pixmap.
138
139 \snippet examples/graphicsview/basicgraphicslayouts/layoutitem.cpp 0
140
141 We use the Q_UNUSED() macro to prevent the compiler from generating
142 warnings regarding unused parameters.
143
144 \snippet examples/graphicsview/basicgraphicslayouts/layoutitem.cpp 1
145
146 The idea behind the \c paint() function is to paint the
147 background rect then paint a rect around the pixmap.
148
149 \snippet examples/graphicsview/basicgraphicslayouts/layoutitem.cpp 2
150
151*/
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