source: trunk/examples/ipc/sharedmemory/dialog.cpp@ 342

/****************************************************************************
**
** Copyright (C) 2009 Nokia Corporation and/or its subsidiary(-ies).
** Contact: Qt Software Information ([email protected])
**
** This file is part of the examples 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 1.0, 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 are unsure which license is appropriate for your use, please
** contact the sales department at [email protected].
** $QT_END_LICENSE$
**
****************************************************************************/

#include "dialog.h"
#include <QFileDialog>
#include <QBuffer>
#include <QtCore/QDebug>

/*!
  \class Dialog

  \brief This class is a simple example of how to use QSharedMemory.

  It is a simple dialog that presents a few buttons. To compile the
  example, run make in qt/examples/ipc. Then run the executable twice
  to create two processes running the dialog. In one of the processes,
  press the button to load an image into a shared memory segment, and
  then select an image file to load. Once the first process has loaded
  and displayed the image, in the second process, press the button to
  read the same image from shared memory. The second process displays
  the same image loaded from its new loaction in shared memory.
*/

/*!
  The class contains a data member \l {QSharedMemory} {sharedMemory},
  which is initialized with the key "QSharedMemoryExample" to force
  all instances of Dialog to access the same shared memory segment.
  The constructor also connects the clicked() signal from each of the
  three dialog buttons to the slot function appropriate for handling
  each button.
*/
//! [0]
Dialog::Dialog(QWidget *parent)
  : QDialog(parent), sharedMemory("QSharedMemoryExample")
{
    ui.setupUi(this);
    connect(ui.loadFromFileButton, SIGNAL(clicked()), SLOT(loadFromFile()));
    connect(ui.loadFromSharedMemoryButton,
            SIGNAL(clicked()),
            SLOT(loadFromMemory()));
    setWindowTitle(tr("SharedMemory Example"));
}
//! [0]

/*!
  This slot function is called when the \tt {Load Image From File...}
  button is pressed on the firs Dialog process. First, it tests
  whether the process is already connected to a shared memory segment
  and, if so, detaches from that segment. This ensures that we always
  start the example from the beginning if we run it multiple times
  with the same two Dialog processes. After detaching from an existing
  shared memory segment, the user is prompted to select an image file.
  The selected file is loaded into a QImage. The QImage is displayed
  in the Dialog and streamed into a QBuffer with a QDataStream.

  Next, it gets a new shared memory segment from the system big enough
  to hold the image data in the QBuffer, and it locks the segment to
  prevent the second Dialog process from accessing it. Then it copies
  the image from the QBuffer into the shared memory segment. Finally,
  it unlocks the shared memory segment so the second Dialog process
  can access it.

  After this function runs, the user is expected to press the \tt
  {Load Image from Shared Memory} button on the second Dialog process.

  \sa loadFromMemory()
 */
//! [1]
void Dialog::loadFromFile()
{
    if (sharedMemory.isAttached())
        detach();

    ui.label->setText(tr("Select an image file"));
    QString fileName = QFileDialog::getOpenFileName(0, QString(), QString(),
                                        tr("Images (*.png *.xpm *.jpg)"));
    QImage image;
    if (!image.load(fileName)) {
        ui.label->setText(tr("Selected file is not an image, please select another."));
        return;
    }
    ui.label->setPixmap(QPixmap::fromImage(image));
//! [1] //! [2]

    // load into shared memory
    QBuffer buffer;
    buffer.open(QBuffer::ReadWrite);
    QDataStream out(&buffer);
    out << image;
    int size = buffer.size();

    if (!sharedMemory.create(size)) {
        ui.label->setText(tr("Unable to create shared memory segment."));
        return;
    }
    sharedMemory.lock();
    char *to = (char*)sharedMemory.data();
    const char *from = buffer.data().data();
    memcpy(to, from, qMin(sharedMemory.size(), size));
    sharedMemory.unlock();
}
//! [2]

/*!