Download Data from URL: Difference between revisions

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{{LangSwitch}}
[[Category:HowTo]]
[[Category:HowTo]]
'''English''' [[Download_Data_from_URL_Bulgarian|Български]] [[Download_Data_from_URL_Korean|한국어]][[Download_Data_from_URL_Persian|فارسی]]
== Introduction ==
== Introduction ==


The following code snippet demonstrates how to download data as {{DocLink|QBteArray}} 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 {{DocLink|QPixmap}} or {{DocLink|QImage}} using method {{DocLinkAnchor|QImage|loadFromData}}.
The following code snippet demonstrates how to download data as {{DocLink|QByteArray}} 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 {{DocLink|QPixmap}} or {{DocLink|QImage}} using method {{DocLink|QImage|loadFromData}}.


Please note that although the name of the class is File''Downloader'' the downloaded data is not saved on the disk as file!
Please note that although the name of the class is File''Downloader'' the downloaded data is not saved on the disk as file!
Line 20: Line 18:
<code>
<code>
QT += network
QT += network
</code>
If you are targeting Symbian devices remember to add the capability for network services.
<code>
symbian:TARGET.CAPABILITY += NetworkServices
</code>
</code>


== filedownloader.h ==
== filedownloader.h ==
<syntaxhighlight lang="cpp">


<code>
#ifndef FILEDOWNLOADER_H
#ifndef FILEDOWNLOADER_H
#define FILEDOWNLOADER_H
#define FILEDOWNLOADER_H
 
#include <QObject>
#include <QObject>
#include <QByteArray>
#include <QByteArray>
#include <QNetworkAccessManager>
#include <QNetworkAccessManager>
#include <QNetworkRequest>
#include <QNetworkRequest>
#include <QNetworkReply>
#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;
};


class FileDownloader : public QObject
  #endif // FILEDOWNLOADER_H
{
  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
</code>


</syntaxhighlight>
== filedownloader.cpp ==
== filedownloader.cpp ==
<syntaxhighlight lang="cpp">


<code>
#include "filedownloader.h"
#include "filedownloader.h"
 
FileDownloader::FileDownloader(QUrl imageUrl, QObject *parent) :
FileDownloader::FileDownloader(QUrl imageUrl, QObject *parent) :
  QObject(parent)
QObject(parent)
{
{
  connect(
connect(
  &m_WebCtrl, SIGNAL (finished(QNetworkReply*)),
  &m_WebCtrl, SIGNAL (finished(QNetworkReply*)),
  this, SLOT (fileDownloaded(QNetworkReply*))
  this, SLOT (fileDownloaded(QNetworkReply*))
   );
   );
 
QNetworkRequest request(imageUrl);
  QNetworkRequest request(imageUrl);
m_WebCtrl.get(request);
  m_WebCtrl.get(request);
}
}
 
FileDownloader::~FileDownloader() { }
FileDownloader::~FileDownloader() { }
 
void FileDownloader::fileDownloaded(QNetworkReply* pReply) {
void FileDownloader::fileDownloaded(QNetworkReply* pReply) {
m_DownloadedData = pReply->readAll();
  m_DownloadedData = pReply->readAll();
//emit a signal
  //emit a signal
pReply->deleteLater();
  pReply->deleteLater();
emit downloaded();
  emit downloaded();
}
}
 
QByteArray FileDownloader::downloadedData() const {
QByteArray FileDownloader::downloadedData() const {
return m_DownloadedData;
  return m_DownloadedData;
}
}
</code>
</syntaxhighlight>


== Usage ==
== Usage ==
Line 98: Line 89:


Declare slot
Declare slot
<syntaxhighlight lang="cpp">


<code>
private slots:
private slots:
  void loadImage();
void loadImage();
</syntaxhighlight>
</code>


Connect signal '''downloaded()''' to the slot
Connect signal '''downloaded()''' to the slot
<syntaxhighlight lang="cpp">


<code>
QUrl imageUrl("http: //qt.digia.com/Documents/1/QtLogo.png");
QUrl imageUrl("http://qt.digia.com/Documents/1/QtLogo.png");
m_pImgCtrl = new FileDownloader(imageUrl, this);
m_pImgCtrl = new FileDownloader(imageUrl, this);
 
connect(m_pImgCtrl, SIGNAL (downloaded()), this, SLOT (loadImage()));
connect(m_pImgCtrl, SIGNAL (downloaded()), this, SLOT (loadImage()));
</syntaxhighlight>
</code>


Load QPixmap from the downloaded data
Load QPixmap from the downloaded data
<syntaxhighlight lang="cpp">


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

Latest revision as of 17:39, 27 April 2024

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Introduction

The following code snippet demonstrates how to download data as QByteArray 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 or QImage using method loadFromData.

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

Important Classes

.pro File

QT += network

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*)),
   this, 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()), this, SLOT (loadImage()));

Load QPixmap from the downloaded data

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