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

[ray.rischpater at nokia.com]

That's actually a good idea --- my model's pretty complex, so I wanted to keep the provider separate so I could re-use it. 

I like the idea of composing the two in the general case --- thanks!

R.

On Nov 19, 2010, at 9:41 AM, ext Jerzy Chalupski wrote:

> QDeclarativeImageProvider is not an QObject, so the model and image
> provider might be implemented in the same class:
> 
> class MyAwesomeModel: public QAbstractItemModel, public
> QDeclarativeImageProvider
> {
> //...
> };
> 
> The upside of this solution is that you can have a single data
> structure, so you don't have to implement data synchronization between
> model and image provider.
> 
> 2010/11/19  <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
>>> 
>>> 
>>> 
>>> 
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>> 
>> 
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