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/*!

    \example itemviews/spinboxdelegate

    \title Spin Box Delegate Example

    The Spin Box Delegate example shows how to create an editor for a custom delegate in

    the model/view framework by reusing a standard Qt editor widget.

    The model/view framework provides a standard delegate that is used by default

    with the standard view classes. For most purposes, the selection of editor

    widgets available through this delegate is sufficient for editing text, boolean

    values, and other simple data types. However, for specific data types, it is

    sometimes necessary to use a custom delegate to either display the data in a

    specific way, or allow the user to edit it with a custom control.

    \image spinboxdelegate-example.png

    This concepts behind this example are covered in the

    \l{model-view-delegate.html}{Delegate Classes} chapter of the

    \l{model-view-programming.html}{Model/View Programming} overview.

    \section1 SpinBoxDelegate Class Definition

    The definition of the delegate is as follows:

    \snippet examples/itemviews/spinboxdelegate/delegate.h 0

    The delegate class declares only those functions that are needed to

    create an editor widget, display it at the correct location in a view,

    and communicate with a model. Custom delegates can also provide their

    own painting code by reimplementing the \c paintEvent() function.

    \section1 SpinBoxDelegate Class Implementation

    Since the delegate is stateless, the constructor only needs to

    call the base class's constructor with the parent QObject as its

    argument:

    \snippet examples/itemviews/spinboxdelegate/delegate.cpp 0

    Since the delegate is a subclass of QItemDelegate, the data it retrieves

    from the model is displayed in a default style, and we do not need to

    provide a custom \c paintEvent().

    The \c createEditor() function returns an editor widget, in this case a

    spin box that restricts values from the model to integers from 0 to 100

    inclusive.

    \snippet examples/itemviews/spinboxdelegate/delegate.cpp 1

    We install an event filter on the spin box to ensure that it behaves in

    a way that is consistent with other delegates. The implementation for

    the event filter is provided by the base class.

    The \c setEditorData() function reads data from the model, converts it

    to an integer value, and writes it to the editor widget.

    \snippet examples/itemviews/spinboxdelegate/delegate.cpp 2

    Since the view treats delegates as ordinary QWidget instances, we have

    to use a static cast before we can set the value in the spin box.

    The \c setModelData() function reads the contents of the spin box, and

    writes it to the model.

    \snippet examples/itemviews/spinboxdelegate/delegate.cpp 3

    We call \l{QSpinBox::interpretText()}{interpretText()} to make sure that

    we obtain the most up-to-date value in the spin box.

    The \c updateEditorGeometry() function updates the editor widget's

    geometry using the information supplied in the style option. This is the

    minimum that the delegate must do in this case.

    \snippet examples/itemviews/spinboxdelegate/delegate.cpp 4

    More complex editor widgets may divide the rectangle available in

    \c{option.rect} between different child widgets if required.

    \section1 The Main Function

    This example is written in a slightly different way to many of the

    other examples supplied with Qt. To demonstrate the use of a custom

    editor widget in a standard view, it is necessary to set up a model

    containing some arbitrary data and a view to display it.

    We set up the application in the normal way, construct a standard item

    model to hold some data, set up a table view to use the data in the

    model, and construct a custom delegate to use for editing:

    \snippet examples/itemviews/spinboxdelegate/main.cpp 0

    The table view is informed about the delegate, and will use it to

    display each of the items. Since the delegate is a subclass of

    QItemDelegate, each cell in the table will be rendered using standard

    painting operations.

    We insert some arbitrary data into the model for demonstration purposes:

    \snippet examples/itemviews/spinboxdelegate/main.cpp 1

    \snippet examples/itemviews/spinboxdelegate/main.cpp 2

    Finally, the table view is displayed with a window title, and we start

    the application's event loop:

    \snippet examples/itemviews/spinboxdelegate/main.cpp 3

    Each of the cells in the table can now be edited in the usual way, but

    the spin box ensures that the data returned to the model is always

    constrained by the values allowed by the spin box delegate.

*/