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/****************************************************************************
**
** Copyright (C) 2009 Nokia Corporation and/or its subsidiary(-ies).
** Contact: Nokia Corporation (qt-info@nokia.com)
**
** This file is part of the documentation of the Qt Toolkit.
**
** $QT_BEGIN_LICENSE:LGPL$
** No Commercial Usage
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** contained in the Technology Preview License Agreement accompanying
** this package.
**
** GNU Lesser General Public License Usage
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** 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.
**
** If you have questions regarding the use of this file, please contact
** Nokia at qt-info@nokia.com.
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** $QT_END_LICENSE$
**
****************************************************************************/
/*!
\example designer/customwidgetplugin
\title Custom Widget Plugin Example
The Custom Widget example shows how to create a custom widget plugin for \QD.
\image customwidgetplugin-example.png
In this example, the custom widget used is based on the
\l{widgets/analogclock}{Analog Clock example}, and does not provide any custom
signals or slots.
\section1 Preparation
To provide a custom widget that can be used with \QD, we need to supply a
self-contained implementation and provide a plugin interface. In this
example, we reuse the \l{widgets/analogclock}{Analog Clock example} for
convenience.
Since custom widgets plugins rely on components supplied with \QD, the
project file that we use needs to contain information about \QD's
library components:
\snippet examples/designer/customwidgetplugin/customwidgetplugin.pro 2
\snippet examples/designer/customwidgetplugin/customwidgetplugin.pro 0
The \c TEMPLATE variable's value makes \c qmake create the custom
widget as a library. Later, we will ensure that the widget will be
recognized as a plugin by Qt by using the Q_EXPORT_PLUGIN2() macro
to export the relevant widget information.
The \c CONFIG variable contains two values, \c designer and \c
plugin:
\list
\o \c designer: Since custom widgets plugins rely on components
supplied with \QD, this value ensures that our plugin links
against \QD's library (\c libQtDesigner.so).
\o \c plugin: We also need to ensure that \c qmake considers the
custom widget a plugin library.
\endlist
When Qt is configured to build in both debug and release modes,
\QD will be built in release mode. When this occurs, it is
necessary to ensure that plugins are also built in release
mode. For that reason we add the \c debug_and_release value to the
\c CONFIG variable. Otherwise, if a plugin is built in a mode that
is incompatible with \QD, it won't be loaded and
installed.
The header and source files for the widget are declared in the usual way,
and we provide an implementation of the plugin interface so that \QD can
use the custom widget:
\snippet examples/designer/customwidgetplugin/customwidgetplugin.pro 3
It is also important to ensure that the plugin is installed in a
location that is searched by \QD. We do this by specifying a
target path for the project and adding it to the list of items to
install:
\snippet doc/src/snippets/code/doc_src_examples_customwidgetplugin.qdoc 0
The custom widget is created as a library, and will be installed
alongside the other \QD plugins when the project is installed
(using \c{make install} or an equivalent installation procedure).
Later, we will ensure that it is recognized as a plugin by \QD by
using the Q_EXPORT_PLUGIN2() macro to export the relevant widget
information.
Note that if you want the plugins to appear in a Visual Studio
integration, the plugins must be built in release mode and their
libraries must be copied into the plugin directory in the install
path of the integration (for an example, see \c {C:/program
files/trolltech as/visual studio integration/plugins}).
For more information about plugins, see the \l {How to
Create Qt Plugins} documentation.
\section1 AnalogClock Class Definition and Implementation
The \c AnalogClock class is defined and implemented in exactly the same
way as described in the \l{widgets/analogclock}{Analog Clock example}.
Since the class is self-contained, and does not require any external
configuration, it can be used without modification as a custom widget in
\QD.
\section1 AnalogClockPlugin Class Definition
The \c AnalogClock class is exposed to \QD through the \c
AnalogClockPlugin class. This class inherits from both QObject and
the QDesignerCustomWidgetInterface class, and implements an
interface defined by QDesignerCustomWidgetInterface:
\snippet examples/designer/customwidgetplugin/customwidgetplugin.h 0
The functions provide information about the widget that \QD can use in
the \l{Getting to Know Qt Designer#WidgetBox}{widget box}.
The \c initialized private member variable is used to record whether
the plugin has been initialized by \QD.
Note that the only part of the class definition that is specific to
this particular custom widget is the class name.
\section1 AnalogClockPlugin Implementation
The class constructor simply calls the QObject base class constructor
and sets the \c initialized variable to \c false.
\snippet examples/designer/customwidgetplugin/customwidgetplugin.cpp 0
\QD will initialize the plugin when it is required by calling the
\c initialize() function:
\snippet examples/designer/customwidgetplugin/customwidgetplugin.cpp 1
In this example, the \c initialized private variable is tested, and only
set to \c true if the plugin is not already initialized. Although, this
plugin does not require any special code to be executed when it is
initialized, we could include such code after the test for initialization.
The \c isInitialized() function lets \QD know whether the plugin is
ready for use:
\snippet examples/designer/customwidgetplugin/customwidgetplugin.cpp 2
Instances of the custom widget are supplied by the \c createWidget()
function. The implementation for the analog clock is straightforward:
\snippet examples/designer/customwidgetplugin/customwidgetplugin.cpp 3
In this case, the custom widget only requires a \c parent to be specified.
If other arguments need to be supplied to the widget, they can be
introduced here.
The following functions provide information for \QD to use to represent
the widget in the widget box.
The \c name() function returns the name of class that provides the
custom widget:
\snippet examples/designer/customwidgetplugin/customwidgetplugin.cpp 4
The \c group() function is used to describe the type of widget that the
custom widget belongs to:
\snippet examples/designer/customwidgetplugin/customwidgetplugin.cpp 5
The widget plugin will be placed in a section identified by its
group name in \QD's widget box. The icon used to represent the
widget in the widget box is returned by the \c icon() function:
\snippet examples/designer/customwidgetplugin/customwidgetplugin.cpp 6
In this case, we return a null icon to indicate that we have no icon
that can be used to represent the widget.
A tool tip and "What's This?" help can be supplied for the custom widget's
entry in the widget box. The \c toolTip() function should return a short
message describing the widget:
\snippet examples/designer/customwidgetplugin/customwidgetplugin.cpp 7
The \c whatsThis() function can return a longer description:
\snippet examples/designer/customwidgetplugin/customwidgetplugin.cpp 8
The \c isContainer() function tells \QD whether the widget is supposed to
be used as a container for other widgets. If not, \QD will not allow the
user to place widgets inside it.
\snippet examples/designer/customwidgetplugin/customwidgetplugin.cpp 9
Most widgets in Qt can contain child widgets, but it only makes sense
to use dedicated container widgets for this purpose in \QD. By returning
\c false, we indicate that the custom widget cannot hold other widgets;
if we returned true, \QD would allow other widgets to be placed inside
the analog clock and a layout to be defined.
The \c domXml() function provides a way to include default settings for
the widget in the standard XML format used by \QD. In this case, we only
specify the widget's geometry:
\snippet examples/designer/customwidgetplugin/customwidgetplugin.cpp 10
If the widget provides a reasonable size hint, it is not necessary to
define it here. In addition, returning an empty string instead of a
\c{<widget>} element will tell \QD not to install the widget in the
widget box.
To make the analog clock widget usable by applications, we implement
the \c includeFile() function to return the name of the header file
containing the custom widget class definition:
\snippet examples/designer/customwidgetplugin/customwidgetplugin.cpp 12
Finally, we use the Q_EXPORT_PLUGIN2() macro to export the \c
AnalogClockPlugin class for use with \QD:
\snippet examples/designer/customwidgetplugin/customwidgetplugin.cpp 13
This macro ensures that \QD can access and construct the custom widget.
Without this macro, there is no way for \QD to use the widget.
It is important to note that you can only use the Q_EXPORT_PLUGIN2()
macro once in any implementation. If you have several custom widgets in
an implementation that you wish to make available to \QD, you will need
to implement \l{QDesignerCustomWidgetCollectionInterface}.
*/
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