qt - how to download and save image via http?

Question

I am trying to download and save some images with Qt in a console appplication. Here is what I got so far, (all code is compiling, but after run, it seems to don't enter to replyFinished() function...)

void Test::start()
{
    std::cout << "start1";
    QNetworkAccessManager *manager = new QNetworkAccessManager();
    connect(manager, SIGNAL(finished(QNetworkReply*)), this, SLOT(replyFinished(QNetworkReply*)));
    manager->get(QNetworkRequest(QUrl("http://www.exylum.mydevil.net/firefox.jpg")));
}

void Test::replyFinished(QNetworkReply* reply)
{
    std::cout << "st";
    QImage* img2 = new QImage();
    img2->loadFromData(reply->readAll());

    if(img2->isNull())
        std::cout << "oops";

    if(img2->save("omg2.jpg", "JPG"))
        std::cout << "saved";
    else
        std::cout << "dont...";
}

Answer 1

Download Image using QNetworkAccessManager

header file

#ifndef QDOWNLOADER_H
#define QDOWNLOADER_H

#include <QObject>
#include <QNetworkAccessManager>
#include <QNetworkRequest>
#include <QNetworkReply>
#include <QFile>
#include <QStringList>

class QDownloader : public QObject
{
    Q_OBJECT
public:
    explicit QDownloader(QObject *parent = 0);
    virtual ~QDownloader();
    void setFile(QString fileURL);

private:
    QNetworkAccessManager *manager;
    QNetworkReply *reply;
    QFile *file;

private slots:
    void onDownloadProgress(qint64,qint64);
    void onFinished(QNetworkReply*);
    void onReadyRead();
    void onReplyFinished();
};

#endif // QDOWNLOADER_H

source file

#include "qdownloader.h"

QDownloader::QDownloader(QObject *parent) :
    QObject(parent)
{
    manager = new QNetworkAccessManager;
}

QDownloader::~QDownloader()
{
    manager->deleteLater();
}

void QDownloader::setFile(QString fileURL)
{
    QString filePath = fileURL;
    QString saveFilePath;
    QStringList filePathList = filePath.split('/');
    QString fileName = filePathList.at(filePathList.count() - 1);
    saveFilePath = QString("C:/Images/" + fileName );

    QNetworkRequest request;
    request.setUrl(QUrl(fileURL));
    reply = manager->get(request);

    file = new QFile;
    file->setFileName(saveFilePath);
    file->open(QIODevice::WriteOnly);

    connect(reply,SIGNAL(downloadProgress(qint64,qint64)),this,SLOT(onDownloadProgress(qint64,qint64)));
    connect(manager,SIGNAL(finished(QNetworkReply*)),this,SLOT(onFinished(QNetworkReply*)));
    connect(reply,SIGNAL(readyRead()),this,SLOT(onReadyRead()));
    connect(reply,SIGNAL(finished()),this,SLOT(onReplyFinished()));
}

void QDownloader::onDownloadProgress(qint64 bytesRead,qint64 bytesTotal)
{
    qDebug(QString::number(bytesRead).toLatin1() +" - "+ QString::number(bytesTotal).toLatin1());
}

void QDownloader::onFinished(QNetworkReply * reply)
{
    switch(reply->error())
    {
        case QNetworkReply::NoError:
        {
            qDebug("file is downloaded successfully.");
        }break;
        default:{
            qDebug(reply->errorString().toLatin1());
        };
    }

    if(file->isOpen())
    {
        file->close();
        file->deleteLater();
    }
}

void QDownloader::onReadyRead()
{
    file->write(reply->readAll());
}

void QDownloader::onReplyFinished()
{
    if(file->isOpen())
    {
        file->close();
        file->deleteLater();
    }
}

Answer 2

This is an old question, but for reference, I'll post a working version of @lwinhtooko's code:

downloader.h:

#pragma once

#include <QFile>
#include <QNetworkAccessManager>
#include <QNetworkRequest>
#include <QNetworkReply>
#include <QObject>
#include <QUrl>

class Downloader : public QObject {
    Q_OBJECT
    QFile *m_file;
    bool m_isReady = true;

public:
    explicit Downloader(QObject *parent = 0) : QObject(parent) {}
    virtual ~Downloader() { delete m_file; }

    void downloadFileFromURL(const QString &url, const QString &filePath);

private slots:
    void onDownloadFileComplete(QNetworkReply *reply);
};

downloader.cpp:

#include "downloader.h"

void Downloader::downloadFileFromURL(const QString &url, const QString &filePath) {
    if (!m_isReady)
        return;
    m_isReady = false;

    const QString fileName = filePath + url.right(url.size() - url.lastIndexOf("/")); // your filePath should end with a forward slash "/"
    m_file = new QFile();
    m_file->setFileName(fileName);
    m_file->open(QIODevice::WriteOnly);
    if (!m_file->isOpen()) {
        m_isReady = true;
        return; // TODO: permission check?
    }

    QNetworkAccessManager *manager = new QNetworkAccessManager;

    QNetworkRequest request;
    request.setUrl(QUrl(url));

    connect(manager, SIGNAL(finished(QNetworkReply *)), this, SLOT(onDownloadFileComplete(QNetworkReply *)));

    manager->get(request);
}

void Downloader::onDownloadFileComplete(QNetworkReply *reply) {
    if (!m_file->isWritable()) {
        m_isReady = true;
        return; // TODO: error check
    }

    m_file->write(reply->readAll());
    m_file->close(); // TODO: delete the file from the system later on
    m_isReady = true;
}

The issue appeared to be the way QNetworkReply was being used.

Answer 3

None of above solution didn't work for me. But i found this Qt wiki page that worked perfectly for all type of data.

Download Data from URL