void UpdateCachedAssets()
{
bool isViewVisible = IsViewLoaded && View.Window != null;
if (!isViewVisible)
{
return;
}
// The preheat window is twice the height of the visible rect.
CGRect preheatRect = CollectionView.Bounds;
preheatRect = preheatRect.Inset(0f, -.5f * preheatRect.Height);
nfloat delta = NMath.Abs(preheatRect.GetMidY() - previousPreheatRect.GetMidY());
if (delta > CollectionView.Bounds.Height / 3.0f)
{
// Compute the assets to start caching and to stop caching.
var addedIndexPaths = new List <NSIndexPath> ();
var removedIndexPaths = new List <NSIndexPath> ();
ComputeDifferenceBetweenRect(previousPreheatRect, preheatRect, removedRect => {
var indexPaths = CollectionView.GetIndexPaths(removedRect);
if (indexPaths != null)
{
removedIndexPaths.AddRange(indexPaths);
}
}, addedRect => {
var indexPaths = CollectionView.GetIndexPaths(addedRect);
if (indexPaths != null)
{
addedIndexPaths.AddRange(indexPaths);
}
});
var assetsToStartCaching = AssetsAtIndexPaths(addedIndexPaths.ToArray());
var assetsToStopCaching = AssetsAtIndexPaths(removedIndexPaths.ToArray());
// Update the assets the PHCachingImageManager is caching.
if (assetsToStartCaching != null)
{
imageManager.StartCaching(assetsToStartCaching, assetGridThumbnailSize, PHImageContentMode.AspectFill, null);
}
if (assetsToStopCaching != null)
{
imageManager.StopCaching(assetsToStopCaching, assetGridThumbnailSize, PHImageContentMode.AspectFill, null);
}
// Store the preheat rect to compare against in the future.
previousPreheatRect = preheatRect;
}
}
void UpdateCachedAssets()
{
bool isViewVisible = IsViewLoaded && View.Window != null;
if (!isViewVisible)
{
return;
}
// The preheat window is twice the height of the visible rect.
CGRect preheatRect = CollectionView.Bounds;
preheatRect = preheatRect.Inset(0, -preheatRect.Height / 2);
// Update only if the visible area is significantly different from the last preheated area.
nfloat delta = NMath.Abs(preheatRect.GetMidY() - previousPreheatRect.GetMidY());
if (delta <= CollectionView.Bounds.Height / 3)
{
return;
}
// Compute the assets to start caching and to stop caching.
var rects = ComputeDifferenceBetweenRect(previousPreheatRect, preheatRect);
var addedAssets = rects.Added
.SelectMany(rect => CollectionView.GetIndexPaths(rect))
.Select(indexPath => FetchResult.ObjectAt(indexPath.Item))
.Cast <PHAsset> ()
.ToArray();
var removedAssets = rects.Removed
.SelectMany(rect => CollectionView.GetIndexPaths(rect))
.Select(indexPath => FetchResult.ObjectAt(indexPath.Item))
.Cast <PHAsset> ()
.ToArray();
// Update the assets the PHCachingImageManager is caching.
imageManager.StartCaching(addedAssets, thumbnailSize, PHImageContentMode.AspectFill, null);
imageManager.StopCaching(removedAssets, thumbnailSize, PHImageContentMode.AspectFill, null);
// Store the preheat rect to compare against in the future.
previousPreheatRect = preheatRect;
}