How to set a QImage object to QML's Image element from C++ side multiple times?

Question

I am have a QImage object in my Qt app on the C++ side of code.

Image {
   id: my_image
   source: ""
}

I have the QML Connections element in which I am getting a QImage sent

Connections {
    target: qimage_supplier
    onNewQImage: {
        recalled_media_image.source = new_qimage_supplied
    }
}

Question:
Is it possible to set a QImage object to the source of a Image QML item? Doing above way where new_qimage_supplied is actually a QImage sent from C++ side, it complains the following:

Error: Cannot assign QImage to QUrl

How can I set a QImage object to Image QML element?

what is image.png in the example where source is set to the imageprovider as image://MyImageProvider/Image.png . the full declaration is like this.Image { source: "image://MyImageProvider/Image.png" } — TheWaterProgrammer
– TheWaterProgrammer, Commented Dec 11, 2017 at 20:38
I have a void SetImage(QImage image) in my QQuickImageProvider derived class which I call from CPP side to set an image whenever available from some processing. — TheWaterProgrammer
– TheWaterProgrammer, Commented Dec 11, 2017 at 20:45
@eyllanesc its a new QIMage I get on C++ side every time with the same height & width but the content is totally different. all I want to do is set the new QImage object on to the Image QML item from C++ side whenever I get a new QImage . thats it. — TheWaterProgrammer
– TheWaterProgrammer, Commented Dec 11, 2017 at 20:52
looks like this QQuickImageProvider derived class way is nice but how to trigger/manually initiate a call to requestImage? — TheWaterProgrammer
– TheWaterProgrammer, Commented Dec 11, 2017 at 20:53

derM · Accepted Answer · 2017-12-11 22:51:14Z

2

This is a quick and dirty example (not for copy and paste!)

// in main.cpp (imports are missing)

class MyImageProvider: public QQuickImageProvider
{
    QImage m_image;
public:
    MyImageProvider(QImage img)
        : QQuickImageProvider(QQuickImageProvider::Image)
        , m_image(img)
    {}

    QImage requestImage(const QString &id, QSize *size, const QSize &requestedSize) override {
        qDebug() << m_image;
        return m_image;
    }
};

int main(int argc, char *argv[])
{
    QGuiApplication app(argc, argv);
    QQmlApplicationEngine engine;   
    engine.addImageProvider("myimg", new MyImageProvider(QImage("C:/.../image.png")));
    engine.load(QUrl(QStringLiteral("main.qml")));

    return app.exec();
}

// in main.qml

ApplicationWindow {
    id: rootWin
    width: 800; height: 600; visible: true

    Image {
        source: "image://myimg/1"
    }
}

The source is:

image://registeredNameOfImageProvider/potentialId

edited Dec 11, 2017 at 22:51

answered Dec 11, 2017 at 20:44

derM

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6 Comments

TheWaterProgrammer Over a year ago

how can I trigger a call to requestImage? I have a method in MyImageProvider to set the new QIMage whenever available. If I could just somehow manually trigger the call to requestImage somehow then the problem is solved for me

derM Over a year ago

The problem is, that afaik the engine caches the images. So you will need to change the source everytime. Change from source: "image://myimg/1" to source = "image://myimg/2" and so on, everytime the image changes.

TheWaterProgrammer Over a year ago

where do I get the id that is 1 or 2. is this the first parameter in requestImage, const QString &id that I need to override ?

TheWaterProgrammer Over a year ago

is it somehow possible to trigger a call to requestImage after setting a potentialId?

TheWaterProgrammer Over a year ago

id is always received as blank in requestImage

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