qtconcurent imagescaling example upgrade

[codebehind]

hello.

i look at the example "imagescaling" and done some upgrade.

well:

image.h (image.cpp has all the implementation)

class ImageData
{
  //... some data for the image size and path
}
 
class MyImage: public QWidget, public ImageData
{
// some function for working with images
}

class ImageData
{
  //... some data for the image size and path
}

class MyImage: public QWidget, public ImageData
{
// some function for working with images
}

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Then I have another class for working with all loaded images.

imagelist.h

class MyLsit:public QWidget
{
//...
}

class MyLsit:public QWidget
{
//...
}

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imageList.cpp

// my function for loading image
MyImage loadImage(const ImageData &data)
{
 MyImage m;
//... things to do on loading images
 return m;
}
 
void MyList::FirstStep()
{
 QList<ImageData> datalist;
 // load data
collection= new QFutureWatcher<Image>((QObject*)this);
collection->setFuture(QtConcurrent::mapped(datalist,loadImage));
// etc
}

// my function for loading image
MyImage loadImage(const ImageData &data)
{
 MyImage m;
//... things to do on loading images
 return m;
}

void MyList::FirstStep()
{
 QList<ImageData> datalist;
 // load data
collection= new QFutureWatcher<Image>((QObject*)this);
collection->setFuture(QtConcurrent::mapped(datalist,loadImage));
// etc
}

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when I compile the project it returns the error:

/usr/lib64/qt-4.4.1/include/QtGui/qwidget.h: In copy constructor ‘MyImage::MyImage(const MyImage&)’:
/usr/lib64/qt-4.4.1/include/QtGui/qwidget.h:750: error: ‘QWidget::QWidget(const QWidget&)’ is private
../qt4/Tools/ShowImg/image.h:18: error: within this context
../qt4/Tools/imgsched.cpp: In function ‘Image LoadImage(ImageData&)’:
../qt4/Tools/imgsched.cpp:12: note: synthesized method ‘MyImage::MyImage(const MyImage&)’ first required here

if I change MyImage with QImage:

QImage loadImage(const ImageData &data){...}

QImage loadImage(const ImageData &data){...}

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it compiles.

I think this is an C++ feature, but i can not work it out.
Any suggestion on how to implement this would be appreciate.
thx!

[caduel]

why does MyImage (need to) inherit from QWidget?

(QWidget -as all QObjects- can not be copied or copy-constructed, which is what your compiler is trying to tell you.)

[codebehind]

i forgot to write a detail:
in MyImage I have overwriten the paintEvent function, because i don't use in my main widget a QLabel object where to put the image.

Is there an another way for displaying image?

[caduel]

you have to separate the scaling from the drawing, ie make a class that contains the image (and associated data), and, if needed, one for displaying the data

Two reasons:
* QWidgets can't be copied (no way about that) - see above
* you must access QWidgets only in the main thread (which means no using QWidgets in QtConcurrent either!)

[codebehind]

ok. thanks for the explanation....
i'll will rework my code

you must access QWidgets only in the main thread (which means no using QWidgets in QtConcurrent either!)

could you tell me where can i read more about this? i have a big hole about this topic.

[caduel]

just read threads