How to set QPixmap in QQuickImageProvider class from another class? - c++

Question

I am developing an application using QML and C++, the goal is to download an image named "test.jpg" from a HTTP server and show it in a QML Image component without saving it in hard disk drive.
The class "AppController" downloads the image "test.jpg" from server and store in a global QPixmap variable named "imageReadFromServer".
#ifndef APPCONTROLLER_H
#define APPCONTROLLER_H
#include <QObject>
class AppController : public QObject
{
Q_OBJECT
public:
AppController(QObject *parent = 0);
Q_INVOKABLE void sendImage(QString _imagePath, QString serverLocation);
Q_INVOKABLE void readImage(QString serverLocation);
private:
QByteArray serverResponse;
QPixmap imageReadFromServer;
};
#endif // APPCONTROLLER_H
To display images on QML Image component I know that it is necessary to use "QQuickImageProvider" class, I have done one class named "ImageProvider" and reimplemented its virtual method QPixmap requestPixmap() to handle when QML requests image showing. To test if everything was working well until now, I used the next example code provided by Qt documentation that returns a QPixmap filled with blue color:
QPixmap ImageProvider::requestPixmap(const QString &id, QSize *size, const QSize &requestedSize)
{
qDebug() << "pixmap requested";
int width = 160;
int height = 100;
if(size)
*size = QSize(width,height);
QPixmap pixmap(requestedSize.width() > 0 ? requestedSize.width() : width,
requestedSize.height() > 0 ? requestedSize.height() : height);
pixmap.fill(QColor("blue").rgba());
//return pixmap;
return pixmap;
}
In main.cpp I added its respective image provider.
engine.addImageProvider(QLatin1String("imagefromserver"), new ImageProvider);
When download button is clicked on QML, it calls ImageProvider class method successfully:
onClicked: {
imageVisualizer.visible = true
imageVisualizer.source = "image://imagefromserver/"
}
What I need is:
When requestPixmap() method from ImageProvider class is called, it should return the global variable imageReadFromServer already stored in AppController class.
I have tried to make AppController class inherits directly from QQuickImageProvider but it didn't work because imageReaderFromServer value was weirdly cleared just before call requestPixmap().
I thought that I could use SIGNALS and SLOTS to pass QPixmap between classes but QQuickImageProvider doesn't inherits from QObject, so I cannot use them.
I appreciate any suggestion.
Thanks.
EDIT
I have again tried to implement QQuickImageProvider inheritance in AppController class. It is already working, the mistake was in main.cpp file, I was declaring image provider as shown below:
AppController applicationController;
QQmlApplicationEngine engine;
engine.addImageProvider(QLatin1String("imagefromserver"), new AppController);
This created a new instance of AppController class, and when I accessed to requestPixmap() function it couldn't get the global QPixmap variable imageReadFromServer because it was created in the instance named applicationController. The solution was to assign the same instance to imageProvider as shown below:
engine.addImageProvider(QLatin1String("imagefromserver"), &applicationController);