Download Data from URL

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Download Data from URL

The following code snippet demonstrates how to download data as "QByteArray":http://doc.qt.io/qt-5.0/qtcore/qbytearray.html from URL. The downloaded data can be saved as a file or converted to appropriate object. For example if an image is downloaded it can be converted to "QPixmap":http://doc.qt.io/qt-5.0/qtgui/qpixmap.html or "QImage":http://doc.qt.io/qt-5.0/qtgui/qimage.html using method "loadFromData()":http://doc.qt.io/qt-5.0/qtgui/qimage.html#loadFromData-2

Please note that although the name of the class is FileDownloader the downloaded data is not saved on the disk as file!

Important Classes

• "QNetworkAccessManager":http://doc.qt.io/qt-5.0/qtnetwork/qnetworkaccessmanager.html
• "QNetworkRequest":http://doc.qt.io/qt-5.0/qtnetwork/qnetworkrequest.html
• "QNetworkReply":http://doc.qt.io/qt-5.0/qtnetwork/qnetworkreply.html
• "QUrl":http://doc.qt.io/qt-5.0/qtcore/qurl.html

.pro File

QT ''= network

If you are targeting Symbian devices remember to add the capability for network services.

symbian:TARGET.CAPABILITY''= NetworkServices

filedownloader.h

#ifndef FILEDOWNLOADER_H
#define FILEDOWNLOADER_H

#include <QObject>
#include <QByteArray>
#include <QNetworkAccessManager>
#include <QNetworkRequest>
#include <QNetworkReply>

class FileDownloader : public QObject
{
 Q_OBJECT
public:
 explicit FileDownloader(QUrl imageUrl, QObject '''parent = 0);

 virtual ~FileDownloader();

 QByteArray downloadedData() const;

signals:
 void downloaded();

private slots:

 void fileDownloaded(QNetworkReply''' pReply);

private:

QNetworkAccessManager m_WebCtrl;

QByteArray m_DownloadedData;

};

#endif // FILEDOWNLOADER_H

filedownloader.cpp

#include "filedownloader.h"

FileDownloader::FileDownloader(QUrl imageUrl, QObject '''parent) :
 QObject(parent)
{
 connect(&m_WebCtrl, SIGNAL (finished(QNetworkReply*)),
 SLOT (fileDownloaded(QNetworkReply*)));

 QNetworkRequest request(imageUrl);
 m_WebCtrl.get(request);
}

FileDownloader::~FileDownloader()
{

}

void FileDownloader::fileDownloaded(QNetworkReply''' pReply)
{
 m_DownloadedData = pReply->readAll();
 //emit a signal
 pReply->deleteLater();
 emit downloaded();
}

QByteArray FileDownloader::downloadedData() const
{
 return m_DownloadedData;
}

Usage

Load Pixmap from URL

• Declare slot

private slots:

void loadImage();

• Connect signal downloaded() to the slot

QUrl imageUrl("http://qt.digia.com/Documents/1/QtLogo.png");
m_pImgCtrl = new FileDownloader(imageUrl, this);

connect(m_pImgCtrl, SIGNAL (downloaded()), SLOT (loadImage()));

• Load QPixmap from the downloaded data

void MainWindow::loadImage()
{
 QPixmap buttonImage;
 buttonImage.loadFromData(m_pImgCtrl->downloadedData());
}