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// Copyright (C) 2016 The Qt Company Ltd.
// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GFDL-1.3-no-invariants-only
/*!
\example itemviews/chart
\title Chart Example
\ingroup examples-itemviews
\brief The Chart example shows how to create a custom view for the model/view framework.
\image chart-example.png
In this example, the items in a table model are represented as slices in a pie chart,
relying on the flexibility of the model/view architecture to handle custom editing
and selection features.
\b{Note that you only need to create a new view class if your data requires a
specialized representation.} You should first consider using a standard QListView,
QTableView, or QTreeView with a custom QItemDelegate subclass if you need to
represent data in a special way.
\omit
\section1 PieView Class Definition
The \c PieView class is a subclass of QAbstractItemView. The base class provides
much of the functionality required by view classes, so we only need to provide
implementations for three public functions: visualRect(), scrollTo(), and
indexAt(). However, the view needs to maintain strict control over its look and
feel, so we also provide implementations for a number of other functions:
\snippet itemviews/chart/pieview.h 0
\section1 PieView Class Implementation
The paint event renders the data from the standard item model as a pie chart.
We interpret the data in the following way:
\list
\li Column 0 contains data in two different roles:
The \l{Qt::ItemDataRole}{DisplayRole} contains a label, and the
\l{Qt::ItemDataRole}{DecorationRole} contains the color of the pie slice.
\li Column 1 contains a quantity which we will convert to the angular extent of
the slice.
\endlist
The figure is always drawn with the chart on the left and the key on
the right. This means that we must try and obtain an area that is wider
than it is tall. We do this by imposing a particular aspect ratio on
the chart and applying it to the available vertical space. This ensures
that we always obtain the maximum horizontal space for the aspect ratio
used.
We also apply fixed size margin around the figure.
We use logical coordinates to draw the chart and key, and position them
on the view using viewports.
\endomit
*/
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