Qt 4.7: mainwindow.cpp Example File (network/torrent/mainwindow.cpp)

Qt Reference Documentation

# mainwindow.cpp Example File

network/torrent/mainwindow.cpp

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     #include <QtGui>

     #include "addtorrentdialog.h"
     #include "mainwindow.h"
     #include "ratecontroller.h"
     #include "torrentclient.h"

     // TorrentView extends QTreeWidget to allow drag and drop.
     class TorrentView : public QTreeWidget
     {
         Q_OBJECT
     public:
         TorrentView(QWidget *parent = 0);

     signals:
         void fileDropped(const QString &fileName);

     protected:
         void dragMoveEvent(QDragMoveEvent *event);
         void dropEvent(QDropEvent *event);
     };

     // TorrentViewDelegate is used to draw the progress bars.
     class TorrentViewDelegate : public QItemDelegate
     {
         Q_OBJECT
     public:
         inline TorrentViewDelegate(MainWindow *mainWindow) : QItemDelegate(mainWindow) {}

         inline void paint(QPainter *painter, const QStyleOptionViewItem &option,
                           const QModelIndex &index ) const
         {
             if (index.column() != 2) {
                 QItemDelegate::paint(painter, option, index);
                 return;
             }

             // Set up a QStyleOptionProgressBar to precisely mimic the
             // environment of a progress bar.
             QStyleOptionProgressBar progressBarOption;
             progressBarOption.state = QStyle::State_Enabled;
             progressBarOption.direction = QApplication::layoutDirection();
             progressBarOption.rect = option.rect;
             progressBarOption.fontMetrics = QApplication::fontMetrics();
             progressBarOption.minimum = 0;
             progressBarOption.maximum = 100;
             progressBarOption.textAlignment = Qt::AlignCenter;
             progressBarOption.textVisible = true;

             // Set the progress and text values of the style option.
             int progress = qobject_cast<MainWindow *>(parent())->clientForRow(index.row())->progress();
             progressBarOption.progress = progress < 0 ? 0 : progress;
             progressBarOption.text = QString().sprintf("%d%%", progressBarOption.progress);

             // Draw the progress bar onto the view.
             QApplication::style()->drawControl(QStyle::CE_ProgressBar, &progressBarOption, painter);
         }
     };

     MainWindow::MainWindow(QWidget *parent)
         : QMainWindow(parent), quitDialog(0), saveChanges(false)
     {
         // Initialize some static strings
         QStringList headers;
         headers << tr("Torrent") << tr("Peers/Seeds") << tr("Progress")
                 << tr("Down rate") << tr("Up rate") << tr("Status");

         // Main torrent list
         torrentView = new TorrentView(this);
         torrentView->setItemDelegate(new TorrentViewDelegate(this));
         torrentView->setHeaderLabels(headers);
         torrentView->setSelectionBehavior(QAbstractItemView::SelectRows);
         torrentView->setAlternatingRowColors(true);
         torrentView->setRootIsDecorated(false);
         setCentralWidget(torrentView);

         // Set header resize modes and initial section sizes
         QFontMetrics fm = fontMetrics();
         QHeaderView *header = torrentView->header();
         header->resizeSection(0, fm.width("typical-name-for-a-torrent.torrent"));
         header->resizeSection(1, fm.width(headers.at(1) + "  "));
         header->resizeSection(2, fm.width(headers.at(2) + "  "));
         header->resizeSection(3, qMax(fm.width(headers.at(3) + "  "), fm.width(" 1234.0 KB/s ")));
         header->resizeSection(4, qMax(fm.width(headers.at(4) + "  "), fm.width(" 1234.0 KB/s ")));
         header->resizeSection(5, qMax(fm.width(headers.at(5) + "  "), fm.width(tr("Downloading") + "  ")));

         // Create common actions
         QAction *newTorrentAction = new QAction(QIcon(":/icons/bottom.png"), tr("Add &new torrent"), this);
         pauseTorrentAction = new QAction(QIcon(":/icons/player_pause.png"), tr("&Pause torrent"), this);
         removeTorrentAction = new QAction(QIcon(":/icons/player_stop.png"), tr("&Remove torrent"), this);

         // File menu
         QMenu *fileMenu = menuBar()->addMenu(tr("&File"));
         fileMenu->addAction(newTorrentAction);
         fileMenu->addAction(pauseTorrentAction);
         fileMenu->addAction(removeTorrentAction);
         fileMenu->addSeparator();
         fileMenu->addAction(QIcon(":/icons/exit.png"), tr("E&xit"), this, SLOT(close()));

         // Help menu
         QMenu *helpMenu = menuBar()->addMenu(tr("&Help"));
         helpMenu->addAction(tr("&About"), this, SLOT(about()));
         helpMenu->addAction(tr("About &Qt"), qApp, SLOT(aboutQt()));

         // Top toolbar
         QToolBar *topBar = new QToolBar(tr("Tools"));
         addToolBar(Qt::TopToolBarArea, topBar);
         topBar->setMovable(false);
         topBar->addAction(newTorrentAction);
         topBar->addAction(removeTorrentAction);
         topBar->addAction(pauseTorrentAction);
         topBar->addSeparator();
         downActionTool = topBar->addAction(QIcon(tr(":/icons/1downarrow.png")), tr("Move down"));
         upActionTool = topBar->addAction(QIcon(tr(":/icons/1uparrow.png")), tr("Move up"));

         // Bottom toolbar
         QToolBar *bottomBar = new QToolBar(tr("Rate control"));
         addToolBar(Qt::BottomToolBarArea, bottomBar);
         bottomBar->setMovable(false);
         downloadLimitSlider = new QSlider(Qt::Horizontal);
         downloadLimitSlider->setRange(0, 1000);
         bottomBar->addWidget(new QLabel(tr("Max download:")));
         bottomBar->addWidget(downloadLimitSlider);
         bottomBar->addWidget((downloadLimitLabel = new QLabel(tr("0 KB/s"))));
         downloadLimitLabel->setFixedSize(QSize(fm.width(tr("99999 KB/s")), fm.lineSpacing()));
         bottomBar->addSeparator();
         uploadLimitSlider = new QSlider(Qt::Horizontal);
         uploadLimitSlider->setRange(0, 1000);
         bottomBar->addWidget(new QLabel(tr("Max upload:")));
         bottomBar->addWidget(uploadLimitSlider);
         bottomBar->addWidget((uploadLimitLabel = new QLabel(tr("0 KB/s"))));
         uploadLimitLabel->setFixedSize(QSize(fm.width(tr("99999 KB/s")), fm.lineSpacing()));

         // Set up connections
         connect(torrentView, SIGNAL(itemSelectionChanged()),
                 this, SLOT(setActionsEnabled()));
         connect(torrentView, SIGNAL(fileDropped(QString)),
                 this, SLOT(acceptFileDrop(QString)));
         connect(uploadLimitSlider, SIGNAL(valueChanged(int)),
                 this, SLOT(setUploadLimit(int)));
         connect(downloadLimitSlider, SIGNAL(valueChanged(int)),
                 this, SLOT(setDownloadLimit(int)));
         connect(newTorrentAction, SIGNAL(triggered()),
                 this, SLOT(addTorrent()));
         connect(pauseTorrentAction, SIGNAL(triggered()),
                 this, SLOT(pauseTorrent()));
         connect(removeTorrentAction, SIGNAL(triggered()),
                 this, SLOT(removeTorrent()));
         connect(upActionTool, SIGNAL(triggered(bool)),
                 this, SLOT(moveTorrentUp()));
         connect(downActionTool, SIGNAL(triggered(bool)),
                 this, SLOT(moveTorrentDown()));

         // Load settings and start
         setWindowTitle(tr("Torrent Client"));
         setActionsEnabled();
         QMetaObject::invokeMethod(this, "loadSettings", Qt::QueuedConnection);
     }

     QSize MainWindow::sizeHint() const
     {
         const QHeaderView *header = torrentView->header();

         // Add up the sizes of all header sections. The last section is
         // stretched, so its size is relative to the size of the width;
         // instead of counting it, we count the size of its largest value.
         int width = fontMetrics().width(tr("Downloading") + "  ");
         for (int i = 0; i < header->count() - 1; ++i)
             width += header->sectionSize(i);

         return QSize(width, QMainWindow::sizeHint().height())
             .expandedTo(QApplication::globalStrut());
     }

     const TorrentClient *MainWindow::clientForRow(int row) const
     {
         // Return the client at the given row.
         return jobs.at(row).client;
     }

     int MainWindow::rowOfClient(TorrentClient *client) const
     {
         // Return the row that displays this client's status, or -1 if the
         // client is not known.
         int row = 0;
         foreach (Job job, jobs) {
             if (job.client == client)
                 return row;
             ++row;
         }
         return -1;
     }

     void MainWindow::loadSettings()
     {
         // Load base settings (last working directory, upload/download limits).
         QSettings settings("Trolltech", "Torrent");
         lastDirectory = settings.value("LastDirectory").toString();
         if (lastDirectory.isEmpty())
             lastDirectory = QDir::currentPath();
         int up = settings.value("UploadLimit").toInt();
         int down = settings.value("DownloadLimit").toInt();
         uploadLimitSlider->setValue(up ? up : 170);
         downloadLimitSlider->setValue(down ? down : 550);

         // Resume all previous downloads.
         int size = settings.beginReadArray("Torrents");
         for (int i = 0; i < size; ++i) {
             settings.setArrayIndex(i);
             QByteArray resumeState = settings.value("resumeState").toByteArray();
             QString fileName = settings.value("sourceFileName").toString();
             QString dest = settings.value("destinationFolder").toString();

             if (addTorrent(fileName, dest, resumeState)) {
                 TorrentClient *client = jobs.last().client;
                 client->setDownloadedBytes(settings.value("downloadedBytes").toLongLong());
                 client->setUploadedBytes(settings.value("uploadedBytes").toLongLong());
             }
         }
     }

     bool MainWindow::addTorrent()
     {
         // Show the file dialog, let the user select what torrent to start downloading.
         QString fileName = QFileDialog::getOpenFileName(this, tr("Choose a torrent file"),
                                                         lastDirectory,
                                                         tr("Torrents (*.torrent);;"
                                                            " All files (*.*)"));
         if (fileName.isEmpty())
             return false;
         lastDirectory = QFileInfo(fileName).absolutePath();

         // Show the "Add Torrent" dialog.
         AddTorrentDialog *addTorrentDialog = new AddTorrentDialog(this);
         addTorrentDialog->setTorrent(fileName);
         addTorrentDialog->deleteLater();
         if (!addTorrentDialog->exec())
             return false;

         // Add the torrent to our list of downloads
         addTorrent(fileName, addTorrentDialog->destinationFolder());
         if (!saveChanges) {
             saveChanges = true;
             QTimer::singleShot(1000, this, SLOT(saveSettings()));
         }
         return true;
     }

     void MainWindow::removeTorrent()
     {
         // Find the row of the current item, and find the torrent client
         // for that row.
         int row = torrentView->indexOfTopLevelItem(torrentView->currentItem());
         TorrentClient *client = jobs.at(row).client;

         // Stop the client.
         client->disconnect();
         connect(client, SIGNAL(stopped()), this, SLOT(torrentStopped()));
         client->stop();

         // Remove the row from the view.
         delete torrentView->takeTopLevelItem(row);
         jobs.removeAt(row);
         setActionsEnabled();

         saveChanges = true;
         saveSettings();
     }

     void MainWindow::torrentStopped()
     {
         // Schedule the client for deletion.
         TorrentClient *client = qobject_cast<TorrentClient *>(sender());
         client->deleteLater();

         // If the quit dialog is shown, update its progress.
         if (quitDialog) {
             if (++jobsStopped == jobsToStop)
                 quitDialog->close();
         }
     }

     void MainWindow::torrentError(TorrentClient::Error)
     {
         // Delete the client.
         TorrentClient *client = qobject_cast<TorrentClient *>(sender());
         int row = rowOfClient(client);
         QString fileName = jobs.at(row).torrentFileName;
         jobs.removeAt(row);

         // Display the warning.
         QMessageBox::warning(this, tr("Error"),
                              tr("An error occurred while downloading %0: %1")
                              .arg(fileName)
                              .arg(client->errorString()));

         delete torrentView->takeTopLevelItem(row);
         client->deleteLater();
     }

     bool MainWindow::addTorrent(const QString &fileName, const QString &destinationFolder,
                                 const QByteArray &resumeState)
     {
         // Check if the torrent is already being downloaded.
         foreach (Job job, jobs) {
             if (job.torrentFileName == fileName && job.destinationDirectory == destinationFolder) {
                 QMessageBox::warning(this, tr("Already downloading"),
                                      tr("The torrent file %1 is "
                                         "already being downloaded.").arg(fileName));
                 return false;
             }
         }

         // Create a new torrent client and attempt to parse the torrent data.
         TorrentClient *client = new TorrentClient(this);
         if (!client->setTorrent(fileName)) {
             QMessageBox::warning(this, tr("Error"),
                                  tr("The torrent file %1 cannot not be opened/resumed.").arg(fileName));
             delete client;
             return false;
         }
         client->setDestinationFolder(destinationFolder);
         client->setDumpedState(resumeState);

         // Setup the client connections.
         connect(client, SIGNAL(stateChanged(TorrentClient::State)), this, SLOT(updateState(TorrentClient::State)));
         connect(client, SIGNAL(peerInfoUpdated()), this, SLOT(updatePeerInfo()));
         connect(client, SIGNAL(progressUpdated(int)), this, SLOT(updateProgress(int)));
         connect(client, SIGNAL(downloadRateUpdated(int)), this, SLOT(updateDownloadRate(int)));
         connect(client, SIGNAL(uploadRateUpdated(int)), this, SLOT(updateUploadRate(int)));
         connect(client, SIGNAL(stopped()), this, SLOT(torrentStopped()));
         connect(client, SIGNAL(error(TorrentClient::Error)), this, SLOT(torrentError(TorrentClient::Error)));

         // Add the client to the list of downloading jobs.
         Job job;
         job.client = client;
         job.torrentFileName = fileName;
         job.destinationDirectory = destinationFolder;
         jobs << job;

         // Create and add a row in the torrent view for this download.
         QTreeWidgetItem *item = new QTreeWidgetItem(torrentView);

         QString baseFileName = QFileInfo(fileName).fileName();
         if (baseFileName.toLower().endsWith(".torrent"))
             baseFileName.remove(baseFileName.size() - 8);

         item->setText(0, baseFileName);
         item->setToolTip(0, tr("Torrent: %1<br>Destination: %2")
                          .arg(baseFileName).arg(destinationFolder));
         item->setText(1, tr("0/0"));
         item->setText(2, "0");
         item->setText(3, "0.0 KB/s");
         item->setText(4, "0.0 KB/s");
         item->setText(5, tr("Idle"));
         item->setFlags(item->flags() & ~Qt::ItemIsEditable);
         item->setTextAlignment(1, Qt::AlignHCenter);

         if (!saveChanges) {
             saveChanges = true;
             QTimer::singleShot(5000, this, SLOT(saveSettings()));
         }
         client->start();
         return true;
     }

     void MainWindow::saveSettings()
     {
         if (!saveChanges)
           return;
         saveChanges = false;

         // Prepare and reset the settings
         QSettings settings("Trolltech", "Torrent");
         settings.clear();

         settings.setValue("LastDirectory", lastDirectory);
         settings.setValue("UploadLimit", uploadLimitSlider->value());
         settings.setValue("DownloadLimit", downloadLimitSlider->value());

         // Store data on all known torrents
         settings.beginWriteArray("Torrents");
         for (int i = 0; i < jobs.size(); ++i) {
             settings.setArrayIndex(i);
             settings.setValue("sourceFileName", jobs.at(i).torrentFileName);
             settings.setValue("destinationFolder", jobs.at(i).destinationDirectory);
             settings.setValue("uploadedBytes", jobs.at(i).client->uploadedBytes());
             settings.setValue("downloadedBytes", jobs.at(i).client->downloadedBytes());
             settings.setValue("resumeState", jobs.at(i).client->dumpedState());
         }
         settings.endArray();
         settings.sync();
     }

     void MainWindow::updateState(TorrentClient::State)
     {
         // Update the state string whenever the client's state changes.
         TorrentClient *client = qobject_cast<TorrentClient *>(sender());
         int row = rowOfClient(client);
         QTreeWidgetItem *item = torrentView->topLevelItem(row);
         if (item) {
             item->setToolTip(0, tr("Torrent: %1<br>Destination: %2<br>State: %3")
                              .arg(jobs.at(row).torrentFileName)
                              .arg(jobs.at(row).destinationDirectory)
                              .arg(client->stateString()));

             item->setText(5, client->stateString());
         }
         setActionsEnabled();
     }

     void MainWindow::updatePeerInfo()
     {
         // Update the number of connected, visited, seed and leecher peers.
         TorrentClient *client = qobject_cast<TorrentClient *>(sender());
         int row = rowOfClient(client);

         QTreeWidgetItem *item = torrentView->topLevelItem(row);
         item->setText(1, tr("%1/%2").arg(client->connectedPeerCount())
                       .arg(client->seedCount()));
     }

     void MainWindow::updateProgress(int percent)
     {
         TorrentClient *client = qobject_cast<TorrentClient *>(sender());
         int row = rowOfClient(client);

         // Update the progressbar.
         QTreeWidgetItem *item = torrentView->topLevelItem(row);
         if (item)
             item->setText(2, QString::number(percent));
     }

     void MainWindow::setActionsEnabled()
     {
         // Find the view item and client for the current row, and update
         // the states of the actions.
         QTreeWidgetItem *item = 0;
         if (!torrentView->selectedItems().isEmpty())
             item = torrentView->selectedItems().first();
         TorrentClient *client = item ? jobs.at(torrentView->indexOfTopLevelItem(item)).client : 0;
         bool pauseEnabled = client && ((client->state() == TorrentClient::Paused)
                                            ||  (client->state() > TorrentClient::Preparing));

         removeTorrentAction->setEnabled(item != 0);
         pauseTorrentAction->setEnabled(item != 0 && pauseEnabled);

         if (client && client->state() == TorrentClient::Paused) {
             pauseTorrentAction->setIcon(QIcon(":/icons/player_play.png"));
             pauseTorrentAction->setText(tr("Resume torrent"));
         } else {
             pauseTorrentAction->setIcon(QIcon(":/icons/player_pause.png"));
             pauseTorrentAction->setText(tr("Pause torrent"));
         }

         int row = torrentView->indexOfTopLevelItem(item);
         upActionTool->setEnabled(item && row != 0);
         downActionTool->setEnabled(item && row != jobs.size() - 1);
     }

     void MainWindow::updateDownloadRate(int bytesPerSecond)
     {
         // Update the download rate.
         TorrentClient *client = qobject_cast<TorrentClient *>(sender());
         int row = rowOfClient(client);
         QString num;
         num.sprintf("%.1f KB/s", bytesPerSecond / 1024.0);
         torrentView->topLevelItem(row)->setText(3, num);

         if (!saveChanges) {
             saveChanges = true;
             QTimer::singleShot(5000, this, SLOT(saveSettings()));
         }
     }

     void MainWindow::updateUploadRate(int bytesPerSecond)
     {
         // Update the upload rate.
         TorrentClient *client = qobject_cast<TorrentClient *>(sender());
         int row = rowOfClient(client);
         QString num;
         num.sprintf("%.1f KB/s", bytesPerSecond / 1024.0);
         torrentView->topLevelItem(row)->setText(4, num);

         if (!saveChanges) {
             saveChanges = true;
             QTimer::singleShot(5000, this, SLOT(saveSettings()));
         }
     }

     void MainWindow::pauseTorrent()
     {
         // Pause or unpause the current torrent.
         int row = torrentView->indexOfTopLevelItem(torrentView->currentItem());
         TorrentClient *client = jobs.at(row).client;
         client->setPaused(client->state() != TorrentClient::Paused);
         setActionsEnabled();
     }

     void MainWindow::moveTorrentUp()
     {
         QTreeWidgetItem *item = torrentView->currentItem();
         int row = torrentView->indexOfTopLevelItem(item);
         if (row == 0)
             return;

         Job tmp = jobs.at(row - 1);
         jobs[row - 1] = jobs[row];
         jobs[row] = tmp;

         QTreeWidgetItem *itemAbove = torrentView->takeTopLevelItem(row - 1);
         torrentView->insertTopLevelItem(row, itemAbove);
         setActionsEnabled();
     }

     void MainWindow::moveTorrentDown()
     {
         QTreeWidgetItem *item = torrentView->currentItem();
         int row = torrentView->indexOfTopLevelItem(item);
         if (row == jobs.size() - 1)
             return;

         Job tmp = jobs.at(row + 1);
         jobs[row + 1] = jobs[row];
         jobs[row] = tmp;

         QTreeWidgetItem *itemAbove = torrentView->takeTopLevelItem(row + 1);
         torrentView->insertTopLevelItem(row, itemAbove);
         setActionsEnabled();
     }

     static int rateFromValue(int value)
     {
         int rate = 0;
         if (value >= 0 && value < 250) {
             rate = 1 + int(value * 0.124);
         } else if (value < 500) {
             rate = 32 + int((value - 250) * 0.384);
         } else if (value < 750) {
             rate = 128 + int((value - 500) * 1.536);
         } else {
             rate = 512 + int((value - 750) * 6.1445);
         }
         return rate;
     }

     void MainWindow::setUploadLimit(int value)
     {
         int rate = rateFromValue(value);
         uploadLimitLabel->setText(tr("%1 KB/s").arg(QString().sprintf("%4d", rate)));
         RateController::instance()->setUploadLimit(rate * 1024);
     }

     void MainWindow::setDownloadLimit(int value)
     {
         int rate = rateFromValue(value);
         downloadLimitLabel->setText(tr("%1 KB/s").arg(QString().sprintf("%4d", rate)));
         RateController::instance()->setDownloadLimit(rate * 1024);
     }

     void MainWindow::about()
     {
         QLabel *icon = new QLabel;
         icon->setPixmap(QPixmap(":/icons/peertopeer.png"));

         QLabel *text = new QLabel;
         text->setWordWrap(true);
         text->setText("<p>The <b>Torrent Client</b> example demonstrates how to"
                       " write a complete peer-to-peer file sharing"
                       " application using Qt's network and thread classes.</p>"
                       "<p>This feature complete client implementation of"
                       " the BitTorrent protocol can efficiently"
                       " maintain several hundred network connections"
                       " simultaneously.</p>");

         QPushButton *quitButton = new QPushButton("OK");

         QHBoxLayout *topLayout = new QHBoxLayout;
         topLayout->setMargin(10);
         topLayout->setSpacing(10);
         topLayout->addWidget(icon);
         topLayout->addWidget(text);

         QHBoxLayout *bottomLayout = new QHBoxLayout;
         bottomLayout->addStretch();
         bottomLayout->addWidget(quitButton);
         bottomLayout->addStretch();

         QVBoxLayout *mainLayout = new QVBoxLayout;
         mainLayout->addLayout(topLayout);
         mainLayout->addLayout(bottomLayout);

         QDialog about(this);
         about.setModal(true);
         about.setWindowTitle(tr("About Torrent Client"));
         about.setLayout(mainLayout);

         connect(quitButton, SIGNAL(clicked()), &about, SLOT(close()));

         about.exec();
     }

     void MainWindow::acceptFileDrop(const QString &fileName)
     {
         // Create and show the "Add Torrent" dialog.
         AddTorrentDialog *addTorrentDialog = new AddTorrentDialog;
         lastDirectory = QFileInfo(fileName).absolutePath();
         addTorrentDialog->setTorrent(fileName);
         addTorrentDialog->deleteLater();
         if (!addTorrentDialog->exec())
             return;

         // Add the torrent to our list of downloads.
         addTorrent(fileName, addTorrentDialog->destinationFolder());
         saveSettings();
     }

     void MainWindow::closeEvent(QCloseEvent *)
     {
         if (jobs.isEmpty())
             return;

         // Save upload / download numbers.
         saveSettings();
         saveChanges = false;

         quitDialog = new QProgressDialog(tr("Disconnecting from trackers"), tr("Abort"), 0, jobsToStop, this);

         // Stop all clients, remove the rows from the view and wait for
         // them to signal that they have stopped.
         jobsToStop = 0;
         jobsStopped = 0;
         foreach (Job job, jobs) {
             ++jobsToStop;
             TorrentClient *client = job.client;
             client->disconnect();
             connect(client, SIGNAL(stopped()), this, SLOT(torrentStopped()));
             client->stop();
             delete torrentView->takeTopLevelItem(0);
         }

         if (jobsToStop > jobsStopped)
             quitDialog->exec();
         quitDialog->deleteLater();
         quitDialog = 0;
     }

     TorrentView::TorrentView(QWidget *parent)
         : QTreeWidget(parent)
     {
         setAcceptDrops(true);
     }

     void TorrentView::dragMoveEvent(QDragMoveEvent *event)
     {
         // Accept file actions with a '.torrent' extension.
         QUrl url(event->mimeData()->text());
         if (url.isValid() && url.scheme().toLower() == "file"
                 && url.path().toLower().endsWith(".torrent"))
             event->acceptProposedAction();
     }

     void TorrentView::dropEvent(QDropEvent *event)
     {
         // Accept drops if the file has a '.torrent' extension and it
         // exists.
         QString fileName = QUrl(event->mimeData()->text()).path();
         if (QFile::exists(fileName) && fileName.toLower().endsWith(".torrent"))
             emit fileDropped(fileName);
     }

     #include "mainwindow.moc"