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2010-05-25T14:21:06Z

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==Extend QObject to create keyboard filter==

<source lang="cpp">
Foundations of Qt Development\Chapter06\eventfilter\main.cpp
/*
* Copyright (c) 2006-2007, Johan Thelin
*
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without modification,
* are permitted provided that the following conditions are met:
*
* * Redistributions of source code must retain the above copyright notice,
* this list of conditions and the following disclaimer.
* * Redistributions in binary form must reproduce the above copyright notice,
* this list of conditions and the following disclaimer in the documentation
* and/or other materials provided with the distribution.
* * Neither the name of APress nor the names of its contributors
* may be used to endorse or promote products derived from this software
* without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
* A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
* CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
* EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
* PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
* PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
* LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
* NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
* SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*
*/
#include <QApplication>
#include <QLineEdit>
#include <QKeyEvent>
class KeyboardFilter : public QObject
{
public:
KeyboardFilter( QObject *parent = 0 ) : QObject( parent ) {}

protected:
bool eventFilter( QObject *dist, QEvent *event )
{
if( event->type() == QEvent::KeyPress )
{
QKeyEvent *keyEvent = static_cast<QKeyEvent*>( event );
if( QString("1234567890").indexOf( keyEvent->text() ) != -1 )
return true;
}
return false;
}
};
int main( int argc, char **argv )
{
QApplication app( argc, argv );

QLineEdit lineEdit;
KeyboardFilter filter;

lineEdit.installEventFilter( &filter );
lineEdit.show();

return app.exec();
}

</source>

==Subclass QEvent==

<source lang="cpp">
/****************************************************************************
**
** Copyright (C) 2009 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.
** $QT_END_LICENSE$
**
****************************************************************************/
#include <QCheckBox>
#include <QMouseEvent>
class MyCheckBox : public QCheckBox
{
public:
void mousePressEvent(QMouseEvent *event);
};
void MyCheckBox::mousePressEvent(QMouseEvent *event)
{
if (event->button() == Qt::LeftButton) {
// handle left mouse button here
} else {
// pass on other buttons to base class
QCheckBox::mousePressEvent(event);
}
}
class MyWidget : public QWidget
{
public:
bool event(QEvent *event);
};
static const int MyCustomEventType = 1099;
class MyCustomEvent : public QEvent
{
public:
MyCustomEvent() : QEvent((QEvent::Type)MyCustomEventType) {}
};
bool MyWidget::event(QEvent *event)
{
if (event->type() == QEvent::KeyPress) {
QKeyEvent *ke = static_cast<QKeyEvent *>(event);
if (ke->key() == Qt::Key_Tab) {
return true;
}
} else if (event->type() == MyCustomEventType) {
MyCustomEvent *myEvent = static_cast<MyCustomEvent *>(event);
return true;
}
return QWidget::event(event);
}
int main()
{
}

</source>

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