- Qt 5.5
- Qt Network
- Network Download Manager Example
- downloadmanager.cpp Example File
- Qt 5.5.1 Reference Documentation

# downloadmanager.cpp Example File

downloadmanager/downloadmanager.cpp

    /****************************************************************************
    **
    ** Copyright (C) 2015 The Qt Company Ltd.
    ** Contact: http://www.qt.io/licensing/
    **
    ** This file is part of the examples of the Qt Toolkit.
    **
    ** $QT_BEGIN_LICENSE:BSD$
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    #include "downloadmanager.h"

    #include <QFileInfo>
    #include <QNetworkRequest>
    #include <QNetworkReply>
    #include <QString>
    #include <QStringList>
    #include <QTimer>
    #include <stdio.h>

    DownloadManager::DownloadManager(QObject *parent)
        : QObject(parent), downloadedCount(0), totalCount(0)
    {
    }

    void DownloadManager::append(const QStringList &urlList)
    {
        foreach (QString url, urlList)
            append(QUrl::fromEncoded(url.toLocal8Bit()));

        if (downloadQueue.isEmpty())
            QTimer::singleShot(0, this, SIGNAL(finished()));
    }

    void DownloadManager::append(const QUrl &url)
    {
        if (downloadQueue.isEmpty())
            QTimer::singleShot(0, this, SLOT(startNextDownload()));

        downloadQueue.enqueue(url);
        ++totalCount;
    }

    QString DownloadManager::saveFileName(const QUrl &url)
    {
        QString path = url.path();
        QString basename = QFileInfo(path).fileName();

        if (basename.isEmpty())
            basename = "download";

        if (QFile::exists(basename)) {
            // already exists, don't overwrite
            int i = 0;
            basename += '.';
            while (QFile::exists(basename + QString::number(i)))
                ++i;

            basename += QString::number(i);
        }

        return basename;
    }

    void DownloadManager::startNextDownload()
    {
        if (downloadQueue.isEmpty()) {
            printf("%d/%d files downloaded successfully\n", downloadedCount, totalCount);
            emit finished();
            return;
        }

        QUrl url = downloadQueue.dequeue();

        QString filename = saveFileName(url);
        output.setFileName(filename);
        if (!output.open(QIODevice::WriteOnly)) {
            fprintf(stderr, "Problem opening save file '%s' for download '%s': %s\n",
                    qPrintable(filename), url.toEncoded().constData(),
                    qPrintable(output.errorString()));

            startNextDownload();
            return;                 // skip this download
        }

        QNetworkRequest request(url);
        currentDownload = manager.get(request);
        connect(currentDownload, SIGNAL(downloadProgress(qint64,qint64)),
                SLOT(downloadProgress(qint64,qint64)));
        connect(currentDownload, SIGNAL(finished()),
                SLOT(downloadFinished()));
        connect(currentDownload, SIGNAL(readyRead()),
                SLOT(downloadReadyRead()));

        // prepare the output
        printf("Downloading %s...\n", url.toEncoded().constData());
        downloadTime.start();
    }

    void DownloadManager::downloadProgress(qint64 bytesReceived, qint64 bytesTotal)
    {
        progressBar.setStatus(bytesReceived, bytesTotal);

        // calculate the download speed
        double speed = bytesReceived * 1000.0 / downloadTime.elapsed();
        QString unit;
        if (speed < 1024) {
            unit = "bytes/sec";
        } else if (speed < 1024*1024) {
            speed /= 1024;
            unit = "kB/s";
        } else {
            speed /= 1024*1024;
            unit = "MB/s";
        }

        progressBar.setMessage(QString::fromLatin1("%1 %2")
                               .arg(speed, 3, 'f', 1).arg(unit));
        progressBar.update();
    }

    void DownloadManager::downloadFinished()
    {
        progressBar.clear();
        output.close();

        if (currentDownload->error()) {
            // download failed
            fprintf(stderr, "Failed: %s\n", qPrintable(currentDownload->errorString()));
        } else {
            printf("Succeeded.\n");
            ++downloadedCount;
        }

        currentDownload->deleteLater();
        startNextDownload();
    }

    void DownloadManager::downloadReadyRead()
    {
        output.write(currentDownload->readAll());
    }