help!: how to display image through http url

JKSH

Hi @nguyenhuy, and welcome!

In C++, you must first download the file using QNetworkAccessManager::get(). Then, use QImage::loadFromData() to convert the downloaded bytes into an image.

JonB

@JKSH
I haven't looked, but can you also do this in a Qt desktop app via stylesheet and something like background-image: url(...), which would be simpler?

J.Hilk

@nguyenhuy You could always change to QML, the Image component will do that for you automatically

One of the 2 really good features of QML that I like, Image and Text, so much better than their c++ counter parts

nguyenhuy

i have created a standard mainboard in qt-creator. and suplied it with the example filedownloader from:
"https://wiki.qt.io/Download_Data_from_URL"
but error: ‘m_pImgCtrl’ was not declared in this scope
and use of undeclared identifier 'm_pImgCtrl'
i don't understand :(

jsulm

@nguyenhuy said in help!: how to display image through http url:

but error: ‘m_pImgCtrl’ was not declared in this scope
and use of undeclared identifier 'm_pImgCtrl'

Please show your code.

SGaist

Hi,

@nguyenhuy said in help!: how to display image through http url:

i have created a standard mainboard in qt-creator. and suplied it with the example filedownloader from:
"http://developer.qt.nokia.com/wiki/Download_Data_from_URL"

You might want to update your links, this one has been dead for quite a while now.

nguyenhuy

here @jsulm tks :)

 **filedownloader.h:**
#ifndef FILEDOWNLOADER_H
#define FILEDOWNLOADER_H

#include <QObject>
#include <QByteArray>
#include <QtNetwork/QNetworkAccessManager>
#include <QtNetwork/QNetworkRequest>
#include <QtNetwork/QNetworkReply>
#include <QUrl>


class filedownloader : public QObject
{
public:
    explicit filedownloader(QUrl imageUrl, QObject);
    virtual ~filedownloader();
    QByteArray downloadedData() const;
signals:
    void downloaded();
private slots:
    void fileDownloaded(QNetworkReply pReply);
private:
    QNetworkAccessManager m_WebCtrl;
    QByteArray m_DownloadedData;
};

#endif // FILEDOWNLOADER_H

**mainwindow.h:**
#ifndef MAINWINDOW_H
#define MAINWINDOW_H
#include <QtWidgets/QMainWindow>
#include <QByteArray>

namespace Ui {
class MainWindow;
}

class mainwindow :public QMainWindow
{
    Q_OBJECT
public:
    explicit mainwindow(QWidget *parent = 0);
    ~mainwindow();
private:
    Ui::MainWindow *ui;
private slots:
    void loadImage();
    void on_pushButton_clicked();
};

#endif // MAINWINDOW_H


**filedownloader.cpp:**

#include "filedownloader.h"


filedownloader::filedownloader(QUrl imageUrl,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 downloaded();
   
}


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

**mainwindow.cpp:**

#include "mainwindow.h"
#include "ui_mainwindow.h"
#include "filedownloader.h"
#include "QUrl"

mainwindow::mainwindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
ui->setupUi(this);

QUrl imageUrl("...");
m_pImgCtrl = new fileDownloaded(imageUrl, this);

connect(m_pImgCtrl, SIGNAL(downloaded()), SLOT(loadImage()));
}
mainwindow::~mainwindow()
{
delete ui;
}

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

#include <QCoreApplication>
#include "mainwindow.h"


int main(int argc, char *argv[])
{
    QCoreApplication a(argc, argv);
    mainwindow w;
    w.show();
    return a.exec();
}

Added proper code tags [ @J-Hilk ]

Christian Ehrlicher

Please use the code tags to make your code readable - currently noone can read anything in your code.

JonB

@nguyenhuy
As @Christian-Ehrlicher has said, please make the effort to use the forum's Code tags button.

Meanwhile, as per the error message, this code uses m_pImgCtrl which looks like a member variable but is not declared in the class in the .h file.

nguyenhuy

@Christian-Ehrlicher oh~ sr i'm newbiee

nguyenhuy

@SGaist yes please

SGaist

@nguyenhuy said in help!: how to display image through http url:

@SGaist yes please

That's up to you to update them, you found them in the first place.

nguyenhuy

i tried i out with
@QbyteArray m_pImgCtrl;

JonB

@nguyenhuy
And?

I think you should be looking at https://wiki.qt.io/Download_Data_from_URL rather than your deceased nokia link. There you will see

m_pImgCtrl = new FileDownloader(imageUrl, this);

so you are supposed to figure for yourself that the member variable declaration will need to be

FileDownloader *m_pImgCtrl;

nguyenhuy

@JonB unknown type name FileDownloader

jsulm

@nguyenhuy Did you include filedownloader.h?

nguyenhuy

@jsulm said in help!: how to display image through http url:

Did you include filedownloader.h

yes, sir

jsulm

@nguyenhuy Please show your current code

nguyenhuy

@jsulm ```
code_text
mainwindow.h

#define MAINWINDOW_H
#include <QtWidgets/QMainWindow>


namespace Ui {
class MainWindow;
}

class mainwindow :public QMainWindow
{
    Q_OBJECT
public:
    explicit mainwindow(QWidget *parent = 0);
    ~mainwindow();
signals:
    void downloaded();

private slots:
    void loadImage();
    void on_pushButton_clicked();
private:
    Ui::MainWindow *ui;
    FileDownloader *m_pImgCtrl;
};

#endif // MAINWINDOW_H

mainwindow.cpp

#include "mainwindow.h"
#include "ui_mainwindow.h"
#include "filedownloader.h"
#include "QUrl"
#include <QtWidgets/QMainWindow>

mainwindow::mainwindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{

QUrl imageUrl("...");
m_pImgCtrl = new FileDownloader(imageUrl, this);

connect(m_pImgCtrl, SIGNAL(downloaded()), SLOT(loadImage()));
}
mainwindow::~mainwindow()
{
delete ui;
}

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

}

jsulm

@nguyenhuy Why did you say that you included filedownloader.h if you did not?!
You have to include it in mainwindow.h as you use it there. Or, as an alternative, make a forward declaration of FileDownloader in mainwindow.h and include filedownloader.h in mainwindow.cpp.
This is basic C++ knowledge...