/**************************************************************************** ** ** Copyright (C) 2010 Nokia Corporation and/or its subsidiary(-ies). ** All rights reserved. ** Contact: Nokia Corporation (qt-info@nokia.com) ** ** This file is part of the documentation of the Qt Toolkit. ** ** $QT_BEGIN_LICENSE:LGPL$ ** Commercial Usage ** Licensees holding valid Qt Commercial licenses may use this file in ** accordance with the Qt Commercial License Agreement provided with the ** Software or, alternatively, in accordance with the terms contained in ** a written agreement between you and Nokia. ** ** GNU Lesser General Public License Usage ** Alternatively, this file may be used under the terms of the GNU Lesser ** General Public License version 2.1 as published by the Free Software ** Foundation and appearing in the file LICENSE.LGPL included in the ** packaging of this file. Please review the following information to ** ensure the GNU Lesser General Public License version 2.1 requirements ** will be met: http://www.gnu.org/licenses/old-licenses/lgpl-2.1.html. ** ** In addition, as a special exception, Nokia gives you certain additional ** rights. These rights are described in the Nokia Qt LGPL Exception ** version 1.1, included in the file LGPL_EXCEPTION.txt in this package. ** ** GNU General Public License Usage ** Alternatively, this file may be used under the terms of the GNU ** General Public License version 3.0 as published by the Free Software ** Foundation and appearing in the file LICENSE.GPL included in the ** packaging of this file. Please review the following information to ** ensure the GNU General Public License version 3.0 requirements will be ** met: http://www.gnu.org/copyleft/gpl.html. ** ** If you have questions regarding the use of this file, please contact ** Nokia at qt-info@nokia.com. ** $QT_END_LICENSE$ ** ****************************************************************************/ /*! \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}. */