Qt文件下载工具

在Qt中实现文件下载功能，通常可以通过多种方式来完成，包括使用 QNetworkAccessManager 和 QNetworkReply 类，或者使用更高级别的 QHttpMultiPart 类。以下是两种常见的实现方法：

方法1：使用 QNetworkAccessManager 和 QNetworkReply
创建 QNetworkAccessManager 对象：这个对象负责管理和处理网络请求。

发送 GET 请求：使用 QNetworkAccessManager 的 get 方法来发送一个GET请求到指定的URL。

接收数据：通过重写槽函数 readyRead 来接收数据。

保存文件：将接收到的数据写入到文件中。

处理完成：当下载完成后，重写 finished 槽函数来处理完成的逻辑。
请添加图片描述


#ifndef DOWNLOAD_DIALOG_H
#define DOWNLOAD_DIALOG_H

#include <QDir>
#include <QDialog>
#include <ui_Downloader.h>

namespace Ui {
class Downloader;
}

class QNetworkReply;
class QNetworkAccessManager;

/**
 * \brief Implements an integrated file downloader with a nice UI
 */
class Downloader : public QWidget
{
    Q_OBJECT

signals:
    void downloadFinished (const QString& url, const QString& filepath);

public:
    explicit Downloader (QWidget* parent = 0);
    ~Downloader();

    bool useCustomInstallProcedures() const;

    QString downloadDir() const;
    void setDownloadDir(const QString& downloadDir);

public slots:
    void setUrlId (const QString& url);
    void startDownload (const QUrl& url);
    void setFileName (const QString& file);
    void setUserAgentString (const QString& agent);
    void setUseCustomInstallProcedures (const bool custom);

private slots:
    void finished();
    void openDownload();
    void installUpdate();
    void cancelDownload();
    void saveFile (qint64 received, qint64 total);
    void calculateSizes (qint64 received, qint64 total);
    void updateProgress (qint64 received, qint64 total);
    void calculateTimeRemaining (qint64 received, qint64 total);

private:
    qreal round (const qreal& input);

private:
    QString m_url;
    uint m_startTime;
    QDir m_downloadDir;
    QString m_fileName;
    Ui::Downloader* m_ui;
    QNetworkReply* m_reply;
    QString m_userAgentString;
    bool m_useCustomProcedures;
    QNetworkAccessManager* m_manager;
};

#endif


#pragma execution_character_set("utf-8")
#include <QDir>
#include <QFile>
#include <QProcess>
#include <QMessageBox>
#include <QNetworkReply>
#include <QDesktopServices>
#include <QNetworkAccessManager>

#include <math.h>

#include "Downloader.h"

static const QString PARTIAL_DOWN (".part");

Downloader::Downloader (QWidget* parent) : QWidget (parent)
{
    m_ui = new Ui::Downloader;
    m_ui->setupUi (this);
    /* Initialize private members */
    m_manager = new QNetworkAccessManager();

    /* Initialize internal values */
    m_url = "";
    m_fileName = "";
    m_startTime = 0;
    m_useCustomProcedures = false;

    /* Set download directory */
    m_downloadDir = QDir::homePath() + "/Downloads/";
    /* Configure the appearance and behavior of the buttons */
    m_ui->openButton->setEnabled (false);
    m_ui->openButton->setVisible (false);
    connect (m_ui->stopButton, SIGNAL (clicked()),
             this,               SLOT (cancelDownload()));
    connect (m_ui->openButton, SIGNAL (clicked()),
             this,               SLOT (installUpdate()));

    /* Resize to fit */
}

Downloader::~Downloader()
{
    delete m_ui;
    delete m_reply;
    delete m_manager;
}

/**
 * Returns \c true if the updater shall not intervene when the download has
 * finished (you can use the \c QSimpleUpdater signals to know when the
 * download is completed).
 */
bool Downloader::useCustomInstallProcedures() const
{
    return m_useCustomProcedures;
}

/**
 * Changes the URL, which is used to indentify the downloader dialog
 * with an \c Updater instance
 *
 * \note the \a url parameter is not the download URL, it is the URL of
 *       the AppCast file
 */
void Downloader::setUrlId (const QString& url)
{
    m_url = url;
}

/**
 * Begins downloading the file at the given \a url
 */
void Downloader::startDownload (const QUrl& url)
{
    /* Reset UI */
    m_ui->progressBar->setValue (0);
    m_ui->stopButton->setText (tr ("Stop"));
    m_ui->downloadLabel->setText (tr ("Downloading updates"));
    m_ui->timeLabel->setText (tr ("Time remaining") + ": " + tr ("unknown"));

    /* Configure the network request */
    QNetworkRequest request (url);
    if (!m_userAgentString.isEmpty())
        request.setRawHeader ("User-Agent", m_userAgentString.toUtf8());

    /* Start download */
    m_reply = m_manager->get (request);
    m_startTime = QDateTime::currentDateTime().toTime_t();

    /* Ensure that downloads directory exists */
    if (!m_downloadDir.exists())
        m_downloadDir.mkpath (".");

    /* Remove old downloads */
    QFile::remove (m_downloadDir.filePath (m_fileName));
    QFile::remove (m_downloadDir.filePath (m_fileName + PARTIAL_DOWN));

    /* Update UI when download progress changes or download finishes */
    connect (m_reply, SIGNAL (downloadProgress (qint64, qint64)),
             this,      SLOT (updateProgress   (qint64, qint64)));
    connect (m_reply, SIGNAL (finished ()),
             this,      SLOT (finished ()));
    connect (m_reply, SIGNAL (redirected       (QUrl)),
             this,      SLOT (startDownload    (QUrl)));

}

/**
 * Changes the name of the downloaded file
 */
void Downloader::setFileName (const QString& file)
{
    m_fileName = file;

    if (m_fileName.isEmpty())
        m_fileName = "QSU_Update.bin";
}

/**
 * Changes the user-agent string used to communicate with the remote HTTP server
 */
void Downloader::setUserAgentString (const QString& agent)
{
    m_userAgentString = agent;
}

void Downloader::finished()
{
    /* Rename file */
    QFile::rename (m_downloadDir.filePath (m_fileName + PARTIAL_DOWN),
                   m_downloadDir.filePath (m_fileName));

    /* Notify application */
    emit downloadFinished (m_url, m_downloadDir.filePath (m_fileName));

    /* Install the update */
    m_reply->close();
    installUpdate();
    setVisible (false);
}

/**
 * Opens the downloaded file.
 * \note If the downloaded file is not found, then the function will alert the
 *       user about the error.
 */
void Downloader::openDownload()
{
    if (!m_fileName.isEmpty())
        QDesktopServices::openUrl (QUrl::fromLocalFile (m_downloadDir.filePath (
                                                            m_fileName)));

    else {
        QMessageBox::critical (this,
                               tr ("Error"),
                               tr ("Cannot find downloaded update!"),
                               QMessageBox::Close);
    }
}

/**
 * Instructs the OS to open the downloaded file.
 *
 * \note If \c useCustomInstallProcedures() returns \c true, the function will
 *       not instruct the OS to open the downloaded file. You can use the
 *       signals fired by the \c QSimpleUpdater to install the update with your
 *       own implementations/code.
 */
void Downloader::installUpdate()
{
    if (useCustomInstallProcedures())
        return;

    /* Update labels */
    m_ui->stopButton->setText    (tr ("Close"));
    m_ui->downloadLabel->setText (tr ("Download complete!"));
    m_ui->timeLabel->setText     (tr ("The installer will open separately")
                                  + "...");

    /* Ask the user to install the download */
    QMessageBox box;
    box.setIcon (QMessageBox::Question);
    box.setDefaultButton   (QMessageBox::Ok);
    box.setStandardButtons (QMessageBox::Ok | QMessageBox::Cancel);
    box.setInformativeText (tr ("Click \"OK\" to begin installing the update"));
    box.setText ("<h3>" +
                 tr ("In order to install the update, you may need to "
                     "quit the application.")
                 + "</h3>");

    /* User wants to install the download */
    if (box.exec() == QMessageBox::Ok) {
        if (!useCustomInstallProcedures())
            openDownload();
    }

    /* Wait */
    else {
        m_ui->openButton->setEnabled (true);
        m_ui->openButton->setVisible (true);
        m_ui->timeLabel->setText (tr ("Click the \"Open\" button to "
                                      "apply the update"));
    }
}

/**
 * Prompts the user if he/she wants to cancel the download and cancels the
 * download if the user agrees to do that.
 */
void Downloader::cancelDownload()
{
    if (!m_reply->isFinished()) {
        QMessageBox box;
        box.setWindowTitle (tr ("Updater"));
        box.setIcon (QMessageBox::Question);
        box.setStandardButtons (QMessageBox::Yes | QMessageBox::No);
        box.setText (tr ("Are you sure you want to cancel the download?"));

        if (box.exec() == QMessageBox::Yes) {
            m_reply->abort();
        }
    }
}

/**
 * Writes the downloaded data to the disk
 */
void Downloader::saveFile (qint64 received, qint64 total)
{
    Q_UNUSED(received);
    Q_UNUSED(total);

    /* Check if we need to redirect */
    QUrl url = m_reply->attribute (
                QNetworkRequest::RedirectionTargetAttribute).toUrl();
    if (!url.isEmpty()) {
        startDownload (url);
        return;
    }

    /* Save downloaded data to disk */
    QFile file (m_downloadDir.filePath (m_fileName + PARTIAL_DOWN));
    if (file.open (QIODevice::WriteOnly | QIODevice::Append)) {
        file.write (m_reply->readAll());
        file.close();
    }
}


/**
 * Calculates the appropiate size units (bytes, KB or MB) for the received
 * data and the total download size. Then, this function proceeds to update the
 * dialog controls/UI.
 */
void Downloader::calculateSizes (qint64 received, qint64 total)
{
    QString totalSize;
    QString receivedSize;

    if (total < 1024)
        totalSize = tr ("%1 bytes").arg (total);

    else if (total < 1048576)
        totalSize = tr ("%1 KB").arg (round (total / 1024));

    else
        totalSize = tr ("%1 MB").arg (round (total / 1048576));

    if (received < 1024)
        receivedSize = tr ("%1 bytes").arg (received);

    else if (received < 1048576)
        receivedSize = tr ("%1 KB").arg (received / 1024);

    else
        receivedSize = tr ("%1 MB").arg (received / 1048576);

    m_ui->downloadLabel->setText (tr ("Downloading updates")
                                  + " (" + receivedSize + " " + tr ("of")
                                  + " " + totalSize + ")");
}

/**
 * Uses the \a received and \a total parameters to get the download progress
 * and update the progressbar value on the dialog.
 */
void Downloader::updateProgress (qint64 received, qint64 total)
{
    if (total > 0) {
        m_ui->progressBar->setMinimum (0);
        m_ui->progressBar->setMaximum (100);
        m_ui->progressBar->setValue ((received * 100) / total);

        calculateSizes (received, total);
        calculateTimeRemaining (received, total);
        saveFile (received, total);
    }

    else {
        m_ui->progressBar->setMinimum (0);
        m_ui->progressBar->setMaximum (0);
        m_ui->progressBar->setValue (-1);
        m_ui->downloadLabel->setText (tr ("Downloading Updates") + "...");
        m_ui->timeLabel->setText (QString ("%1: %2")
                                  .arg (tr ("Time Remaining"))
                                  .arg (tr ("Unknown")));
    }
}

/**
 * Uses two time samples (from the current time and a previous sample) to
 * calculate how many bytes have been downloaded.
 *
 * Then, this function proceeds to calculate the appropiate units of time
 * (hours, minutes or seconds) and constructs a user-friendly string, which
 * is displayed in the dialog.
 */
void Downloader::calculateTimeRemaining (qint64 received, qint64 total)
{
    uint difference = QDateTime::currentDateTime().toTime_t() - m_startTime;

    if (difference > 0) {
        QString timeString;
        qreal timeRemaining = total / (received / difference);

        if (timeRemaining > 7200) {
            timeRemaining /= 3600;
            int hours = int (timeRemaining + 0.5);

            if (hours > 1)
                timeString = tr ("about %1 hours").arg (hours);
            else
                timeString = tr ("about one hour");
        }

        else if (timeRemaining > 60) {
            timeRemaining /= 60;
            int minutes = int (timeRemaining + 0.5);

            if (minutes > 1)
                timeString = tr ("%1 minutes").arg (minutes);
            else
                timeString = tr ("1 minute");
        }

        else if (timeRemaining <= 60) {
            int seconds = int (timeRemaining + 0.5);

            if (seconds > 1)
                timeString = tr ("%1 seconds").arg (seconds);
            else
                timeString = tr ("1 second");
        }

        m_ui->timeLabel->setText (tr ("Time remaining") + ": " + timeString);
    }
}

/**
 * Rounds the given \a input to two decimal places
 */
qreal Downloader::round (const qreal& input)
{
    return roundf (input * 100) / 100;
}

QString Downloader::downloadDir() const
{
    return m_downloadDir.absolutePath();
}

void Downloader::setDownloadDir(const QString& downloadDir)
{
    if(m_downloadDir.absolutePath() != downloadDir) {
        m_downloadDir = downloadDir;
    }
}

/**
 * If the \a custom parameter is set to \c true, then the \c Downloader will not
 * attempt to open the downloaded file.
 *
 * Use the signals fired by the \c QSimpleUpdater to implement your own install
 * procedures.
 */
void Downloader::setUseCustomInstallProcedures (const bool custom)
{
    m_useCustomProcedures = custom;
}

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