[Qt-qml] Returning a QImage to QML from C++ for a ListView delegate...

[ray.rischpater at nokia.com]

Actually, you can return different images using the QDeclarativeImageProvider and a C++ model --- simply have a role in the model return a different string resource name for each model item (e.g., "image://model/1.png", "image://model/2.png", and so forth), and then have the image provider return the appropriate image from the model. If you want to be a bit faster, you can even have your image provider use a QMap<QString, QModelIndex> to map from the image's name in the model to the image. Based on Juha's feedback, I've got code running now I'm planning on cleaning up a bit and posting to my blog in the near future. The crux of the code is the requestPixmap method, which looks like this:

class QAbstractItemModel;

class ModelIndexProvider : public QObject, public QDeclarativeImageProvider
{
    Q_OBJECT
public:
    ModelIndexProvider(QAbstractItemModel& model, int pathRole, int pixmapRole, QObject* parent = 0);
    ~ModelIndexProvider();
    QPixmap requestPixmap(const QString& id, QSize* size, const QSize& requestedSize);

public slots:
    void dataUpdated(const QModelIndex & topLeft, const QModelIndex & bottomRight);
    void dataDeleted(const QModelIndex & parent, int start, int end);
    void dataReset();

private:
    QAbstractItemModel& mModel;
    int mPathRole;
    int mPixmapRole;
    QMap<QString, QModelIndex> mPixmapIndex;
};

QPixmap ModelIndexProvider::requestPixmap(const QString& id, QSize* size, const QSize& requestedSize)
{
    QString key = QString("image://model/%1").arg(id);
    QModelIndex index = mPixmapIndex[key];
    QPixmap image = mModel.data(index, mPixmapRole).value<QPixmap>();
    QPixmap result;

    if (requestedSize.isValid()) {
        result = image.scaled(requestedSize, Qt::KeepAspectRatio);
    } else {
        result = image;
    }
    *size = result.size();
    return result;
}

Of course, the provider should be a QObject and connect to the model so that when the model changes the pixmap index gets updated and so forth, but that's pretty easy. 

Thanks again to Juha for the suggestion!

On Nov 18, 2010, at 10:56 PM, ext Tuomas Niinistö wrote:

> Juha Turunen <turunen at ...> writes:
> 
>> 
>> Hi Ray,
>> 
>> [ Use QDeclarativeImageProvider ]
>> 
>> On Fri, Nov 12, 2010 at 7:42 PM,  <ray.rischpater at ...> wrote:
>>> [ Question about returning images from models ]
>>> Nokia Research Center Palo Alto
> 
> Hi,
> 
> I have faced the same problem as Ray. And think that the
> QDeclarativeImageProvider does not help here, at least not directly.
> 
> When you have a list object existing in native C++ side and you wan't to
> populate the QML ListView with it. For "normal" data like integers and strings
> it works fine by using QDeclarativeListProperty.
> 
> But the problem comes when you want to have an individual image for each list
> item. With QDeclarativeImageProvider you can populate the list items with the
> same image instance, but how to have an individual image for each item seems to
> be problematic.
> 
> Br, Tuomas
> 
> 
> 
> 
> _______________________________________________
> Qt-qml mailing list
> Qt-qml at trolltech.com
> http://lists.trolltech.com/mailman/listinfo/qt-qml