C++/Qt/QEvent

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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.
*
*/
  1. include <QApplication>
  2. include <QLineEdit>
  3. 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.
    • $QT_END_LICENSE$
                                                                                                                                                        • /
  1. include <QCheckBox>
  2. 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>