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+
+/*!
+ \example itemviews/combowidgetmapper
+ \title Combo Widget Mapper Example
+
+ The Delegate Widget Mapper example shows how to use a custom delegate to
+ map information from a model to specific widgets on a form.
+
+ \image combo-widget-mapper.png
+
+ In the \l{Simple Widget Mapper Example}, we showed the basic use of a
+ widget mapper to relate data exposed by a model to simple input widgets
+ in a user interface. However, sometimes we want to use input widgets that
+ expose data as choices to the user, such as QComboBox, and we need a way
+ to relate their input to the values stored in the model.
+
+ This example is very similar to the \l{Simple Widget Mapper Example}.
+ Again, we create a \c Window class with an almost identical user interface,
+ except that, instead of providing a spin box so that each person's age
+ can be entered, we provide a combo box to allow their addresses to be
+ classified as "Home", "Work" or "Other".
+
+ \section1 Window Class Definition
+
+ The class provides a constructor, a slot to keep the buttons up to date,
+ and a private function to set up the model:
+
+ \snippet examples/itemviews/combowidgetmapper/window.h Window definition
+
+ In addition to the QDataWidgetMapper object and the controls used to make
+ up the user interface, we use a QStandardItemModel to hold our data and
+ a QStringListModel to hold information about the types of address that
+ can be applied to each person's data.
+
+ \section1 Window Class Implementation
+
+ The constructor of the \c Window class can be explained in three parts.
+ In the first part, we set up the widgets used for the user interface:
+
+ \snippet examples/itemviews/combowidgetmapper/window.cpp Set up widgets
+
+ Note that we set up the mapping the combo box in the same way as for other
+ widgets, but that we apply its own model to it so that it will display
+ data from its own model, the \c typeModel, rather than from the model
+ containing data about each person.
+
+ Next, we set up the widget mapper, relating each input widget to a column
+ in the model specified by the call to \l{QDataWidgetMapper::}{setModel()}:
+
+ \snippet examples/itemviews/combowidgetmapper/window.cpp Set up the mapper
+
+ For the combo box, we pass an extra argument to tell the widget mapper
+ which property to relate to values from the model. As a result, the user
+ is able to select an item from the combo box, and the corresponding
+ value stored in the widget's \c currentIndex property will be stored in
+ the model.
+
+ \omit
+ However, we also set a delegate on the mapper. As with \l{Delegate Classes},
+ this changes the way that data is presented to the user. In this case, the
+ delegate acts as a proxy between the mapper and the input widgets,
+ translating the data into a suitable form for the combo box but not
+ interfering with the other input widgets. The implementation is shown later.
+ \endomit
+
+ The rest of the constructor is very similar to that of the
+ \l{Simple Widget Mapper Example}:
+
+ \snippet examples/itemviews/combowidgetmapper/window.cpp Set up connections and layouts
+
+ The model is initialized in the window's \c{setupModel()} function. Here,
+ we create a standard model with 5 rows and 3 columns. In each row, we
+ insert a name, address, and a value that indicates the type of address.
+ The address types are stored in a string list model.
+
+ \snippet examples/itemviews/combowidgetmapper/window.cpp Set up the model
+
+ As we insert each row into the model, like a record in a database, we
+ store values that correspond to items in \c typeModel for each person's
+ address type. When the widget mapper reads these values from the final
+ column of each row, it will need to use them as references to values in
+ \c typeModel, as shown in the following diagram. This is where the
+ delegate is used.
+
+ \image widgetmapper-combo-mapping.png
+
+ We show the implementation of the \c{updateButtons()} slot for
+ completeness:
+
+ \snippet examples/itemviews/combowidgetmapper/window.cpp Slot for updating the buttons
+
+ \omit
+ \section1 Delegate Class Definition and Implementation
+
+ The delegate we use to mediate interaction between the widget mapper and
+ the input widgets is a small QItemDelegate subclass:
+
+ \snippet examples/itemviews/combowidgetmapper/delegate.h Delegate class definition
+
+ This provides implementations of the two standard functions used to pass
+ data between editor widgets and the model (see the \l{Delegate Classes}
+ documentation for a more general description of these functions).
+
+ Since we only provide an empty implementation of the constructor, we
+ concentrate on the other two functions.
+
+ The \l{QItemDelegate::}{setEditorData()} implementation takes the data
+ referred to by the model index supplied and processes it according to
+ the presence of a \c currentIndex property in the editor widget:
+
+ \snippet examples/itemviews/combowidgetmapper/delegate.cpp setEditorData implementation
+
+ If, like QComboBox, the editor widget has this property, it is set using
+ the value from the model. Since we are passing around QVariant values,
+ the strings stored in the model are automatically converted to the integer
+ values needed for the \c currentIndex property.
+
+ As a result, instead of showing "0", "1" or "2" in the combo box, one of
+ its predefined set of items is shown. We call QItemDelegate::setEditorData()
+ for widgets without the \c currentIndex property.
+
+ The \l{QItemDelegate::}{setModelData()} implementation performs the reverse
+ process, taking the value stored in the widget's \c currentIndex property
+ and storing it back in the model:
+
+ \snippet examples/itemviews/combowidgetmapper/delegate.cpp setModelData implementation
+ \endomit
+
+ \section1 Summary and Further Reading
+
+ The use of a separate model for the combo box provides a menu of choices
+ that are separate from the data stored in the main model. Using a named
+ mapping that relates the combo box's \c currentIndex property to a column
+ in the model effectively allows us to store a look-up value in the model.
+
+ However, when reading the model outside the context of the widget mapper,
+ we need to know about the \c typeModel to make sense of these look-up
+ values. It would be useful to be able to store both the data and the
+ choices held by the \c typeModel in one place.
+ This is covered by the \l{SQL Widget Mapper Example}.
+*/