Implementing File Downolad Functionality with Qt Network Module

Approach Overview

The implementation folllows a structured approach to handle HTTP file downloads:

1. Initially conceal the progress indicator
2. Upon triggering the download action, extract the URL, prepare the output file, and construct the network request
3. Dispatch the request and establish signal-slot connections for data reading, progress updates, and completion handling
4. Process the incoming response data and write it to the designated file
5. Once complete, hide the progress bar, finlaize the file, and clean up network resources

Header File Implementation

#ifndef FILEDOWNLOADER_H
#define FILEDOWNLOADER_H

#include <qmainwindow>
#include <qnetworkaccessmanager>
#include <qnetworkrequest>
#include <qnetworkreply>
#include <qfile>

namespace Ui {
    class FileDownloader;
}

class FileDownloader : public QMainWindow
{
    Q_OBJECT
    
public:
    explicit FileDownloader(QWidget *parent = nullptr);
    ~FileDownloader();
    
private:
    Ui::FileDownloader *ui;
    QNetworkAccessManager *networkManager;
    QFile *outputFile;
    QNetworkReply *httpResponse;

private slots:
    void initiateDownload();
    void updateDownloadProgress(qint64 bytesReceived, qint64 bytesTotal);
    void processReadyData();
    void finalizeDownload();
};

#endif // FILEDOWNLOADER_H
</qfile></qnetworkreply></qnetworkrequest></qnetworkaccessmanager></qmainwindow>

Source File Implementation

#include "FileDownloader.h"
#include "ui_FileDownloader.h"
#include <qurl>
#include <qstring>
#include <qfileinfo>
#include <qfile>
#include <qdebug>

FileDownloader::FileDownloader(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::FileDownloader)
{
    ui->setupUi(this);
    networkManager = new QNetworkAccessManager(this);
    ui->progressBar->setVisible(false);
    connect(ui->downloadButton, &QPushButton::clicked, this, &FileDownloader::initiateDownload);
}

void FileDownloader::initiateDownload()
{
    QString urlString = ui->urlInput->text();
    QUrl url(urlString);

    QFileInfo fileInfo(url.path());
    QString fileName = fileInfo.fileName();
    outputFile = new QFile(fileName);

    if (!outputFile->open(QIODevice::WriteOnly))
    {
        qWarning() << "Failed to create output file";
        delete outputFile;
        outputFile = nullptr;
        return;
    }

    QNetworkRequest request;
    request.setUrl(url);

    httpResponse = networkManager->get(request);
    connect(httpResponse, &QNetworkReply::readyRead, 
            this, &FileDownloader::processReadyData);
    connect(httpResponse, &QNetworkReply::downloadProgress,
            this, &FileDownloader::updateDownloadProgress);
    connect(httpResponse, &QNetworkReply::finished,
            this, &FileDownloader::finalizeDownload);
}

void FileDownloader::updateDownloadProgress(qint64 bytesReceived, qint64 bytesTotal)
{
    ui->progressBar->setMaximum(bytesTotal);
    ui->progressBar->setValue(bytesReceived);
}

void FileDownloader::processReadyData()
{
    if (outputFile)
    {
        outputFile->write(httpResponse->readAll());
        ui->progressBar->setVisible(true);
    }
}

void FileDownloader::finalizeDownload()
{
    ui->progressBar->setVisible(false);
    if (outputFile)
    {
        outputFile->flush();
        outputFile->close();
        delete outputFile;
        outputFile = nullptr;
    }
    httpResponse->deleteLater();
}

FileDownloader::~FileDownloader()
{
    delete ui;
}
</qdebug></qfile></qfileinfo></qstring></qurl>

Application Entry Point

#include <qapplication>
#include "FileDownloader.h"

int main(int argc, char *argv[])
{
    QApplication app(argc, argv);
    FileDownloader downloaderWindow;
    downloaderWindow.show();
    
    return app.exec();
}
</qapplication>