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    41 

    42 /*!

    43     \example itemviews/chart

    44     \title Chart Example

    45 

    46     The Chart example shows how to create a custom view for the model/view framework.

    47 

    48     \image chart-example.png

    49 

    50     In this example, the items in a table model are represented as slices in a pie chart,

    51     relying on the flexibility of the model/view architecture to handle custom editing

    52     and selection features.

    53 

    54     \bold{Note that you only need to create a new view class if your data requires a

    55     specialized representation.} You should first consider using a standard QListView,

    56     QTableView, or QTreeView with a custom QItemDelegate subclass if you need to

    57     represent data in a special way.

    58 

    59     \omit

    60     \section1 PieView Class Definition

    61 

    62     The \c PieView class is a subclass of QAbstractItemView. The base class provides

    63     much of the functionality required by view classes, so we only need to provide

    64     implementations for three public functions: visualRect(), scrollTo(), and

    65     indexAt(). However, the view needs to maintain strict control over its look and

    66     feel, so we also provide implementations for a number of other functions:

    67 

    68     \snippet examples/itemviews/chart/pieview.h 0

    69 

    70 

    71 

    72     \section1 PieView Class Implementation

    73 

    74     The paint event renders the data from the standard item model as a pie chart.

    75     We interpret the data in the following way:

    76 

    77     \list

    78     \o Column 0 contains data in two different roles:

    79        The \l{Qt::ItemDataRole}{DisplayRole} contains a label, and the

    80        \l{Qt::ItemDataRole}{DecorationRole} contains the color of the pie slice.

    81     \o Column 1 contains a quantity which we will convert to the angular extent of

    82        the slice.

    83     \endlist

    84 

    85     The figure is always drawn with the chart on the left and the key on

    86     the right. This means that we must try and obtain an area that is wider

    87     than it is tall. We do this by imposing a particular aspect ratio on

    88     the chart and applying it to the available vertical space. This ensures

    89     that we always obtain the maximum horizontal space for the aspect ratio

    90     used.

    91     We also apply fixed size margin around the figure.

    92 

    93     We use logical coordinates to draw the chart and key, and position them

    94     on the view using viewports.

    95     \endomit

    96 */