I am using QT 4.6
Nokia N8 (Symbian)

I am having a bit of a memory issue using the SlidingStackedWidget to hold nine list view widgets, that each display approx 20 items.

To try and conserve memory I am loading only the images for the currently displayed widget.
I am controlling the loading/unloading by capturing the widget event for show and hide, and using this to repolulate my model for the list view.

I am also using the PixmapCache as a mechanism to cache images that I have loaded, I have set my cache size to 2048k

My code for loading the pixmap, and populating / clearing the list model is listed below.

When I run this on the Nokia N8, and transition between widgets, I very quickly run out of memory, when loading images.

From my observations (I have included the code I use to trace memory usage) there is a mismatch between the amount of data allocated between
the populateModel and clearModel methods. When I transition to a new screen the memory allways increases, and when I clear the model, it never seems to remove enough memory.

1. I am concerned that I am misusing the PixmapCache, the help states,
"QPixmaps are automatically added to the QPixmapCache when loaded from a file; the key used is internal and can not be acquired."
Should I be bothering to cache Pixmaps as I load them, as it would appear the system is already doing this for me?

2. Does the models appendRow method take ownership of the item data?
do I need to clear the model row by row, prior to calling clear?

3. can anyone point out where I am leaking memory?

thanks in advance

Guus Davidson

Qt Code: 
  1. #ifdef Q_OS_SYMBIAN
  2.         TInt mem, size, limit;
  3.         User::Heap().AllocSize(mem);
  4.         size = User::Heap().Size();
  5.         limit = User::Heap().MaxLength();
  6.  
  7.         qDebug() << QString("Heap Mem : %1").arg(mem);
  8.         qDebug() << QString("Heap Size : %1").arg(size);
  9.         qDebug() << QString("Heap Limit : %1").arg(limit);
  10. #endif
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Qt Code: 
  1. QPixmap FileImageCache::getPixmap(const QString& key)
  2. {   
  3.     QPixmap pm;
  4.     if (!QPixmapCache::find(key, &pm)) 
  5. {
  6.         pm.load(diskCacheDirectory + "//" +key);
  7.         bool result = QPixmapCache::insert(key, pm);
  8.     return pm;
  9. }
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Qt Code: 
  1. void DisplayWidget::populateModel()
  2. {    
  3.     if(iModelCleared == true)
  4.     {
  5.         BaseDisplayWidget::populateModel();
  6.  
  7.         QStandardItemModel* model = dynamic_cast<QStandardItemModel*>(iListView->model());
  8.         int defaultIconCount = 0;
  9.         if(model != 0 && iAppStoreChannel != 0)
  10.         {
  11.             QList<AppstoreItem*> items = iAppStoreChannel->getItems();
  12.  
  13.             int count = items.count();
  14.             AppstoreItem* currentItem = 0;
  15.  
  16.             for(int i = 0; i < count ; i++)
  17.             {
  18.                 bool defaultIconUsed = true;
  19.                 currentItem = items.at(i);
  20.  
  21.                 QString url = currentItem->getIconUrl();
  22.                 QIcon icon_image;
  23.                 if(url.length() > 0)
  24.                 {
  25.                     QString key = iImageCache->getKeyForImageLocation(url);
  26.                     if(iImageCache->containsKey(key) == true)
  27.                     {
  28.                         QPixmap pixmap= iImageCache->getPixmap(key);
  29.  
  30.                         if(!pixmap.isNull())
  31.                         {
  32.                             defaultIconUsed = false;
  33.                             icon_image.addPixmap(pixmap);
  34.                         }
  35.                         else
  36.                         {
  37.                             defaultIconCount ++;
  38.                         }
  39.                     }
  40.                 }
  41.  
  42.                 isdefaultIcon.append(defaultIconUsed);
  44.  
  45.                 item->setData(currentItem ->getHeadline(),ChannelListViewDelegate::headerTextRole);
  46.                 item->setData(currentItem ->getDescription(),ChannelListViewDelegate::subHeaderTextrole);
  47.                 if(icon_image.isNull())
  48.                 {
  49.                     item->setData(*icon_default,ChannelListViewDelegate::IconRole);
  50.                 }
  51.                 else
  52.                 {
  53.                     item->setData(icon_image,ChannelListViewDelegate::IconRole);
  54.                 }
  55.                 model->appendRow(item);
  56.             }
  57.          }
  58.     }
  59. }
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Qt Code: 
  1. void DisplayWidget::clearModel()
  2. {
  3.     if(iModelCleared == false)
  4.     {      
  5.         QStandardItemModel* ptr = dynamic_cast<QStandardItemModel*>(iListView->model());
  6.         if(ptr != 0)
  7.         {
  8.             ptr->clear();
  9.             iModelCleared = true;
  10.             delete ptr;
  11.         }
  12.     }
  13. }
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