/// <param name="fetchDataCallback">Callback used when more data is requested for the cache</param>
/// <param name="updateCountCallback">Callback used to calculate the total number of items that exist outside the cache</param>
/// <param name="cacheBatchSize">Cache batch size</param>
public VirtualizedDataSource(FetchDataCallbackHandler <T> fetchDataCallback, UpdateCountCallbackHandler updateCountCallback, int cacheBatchSize = 10)
{
// The ItemCacheManager does most of the heavy lifting. We pass it a callback that it will use to actually fetch data, and the max size of a request
_itemCache = new ItemCacheManager <T>(fetchDataCallback, cacheBatchSize);
_itemCache.CacheChanged += ItemCache_CacheChanged;
_updateCountCallback = updateCountCallback;
UpdateCount();
}
private FileDataSource()
{
//Setup the dispatcher for the UI thread
_dispatcher = Windows.UI.Xaml.Window.Current.Dispatcher;
// The ItemCacheManager does most of the heavy lifting. We pass it a callback that it will use to actually fetch data, and the max size of a request
this.itemCache = new ItemCacheManager<FileItem>(fetchDataCallback, 50);
this.itemCache.CacheChanged += ItemCache_CacheChanged;
}
// Handles a change notification for the list of files from the OS
public async void ResetCollection()
{
// Update the selection cache to match the filesystem after the updates
await RemapSelection();
// Unhook the old change notification
if (itemCache != null)
{
this.itemCache.CacheChanged -= ItemCache_CacheChanged;
}
// Create a new instance of the cache manager
this.itemCache = new ItemCacheManager<FileItem>(fetchDataCallback, 50);
this.itemCache.CacheChanged += ItemCache_CacheChanged;
if (CollectionChanged != null)
{
CollectionChanged(this, new NotifyCollectionChangedEventArgs(NotifyCollectionChangedAction.Reset));
}
}
public void Dispose()
{
_itemCache = null;
}
//Required for the IItemsRangeInfo interface
public void Dispose()
{
itemCache = null;
}
// Called after a reset to figure out the new indexes for the selected items
private async Task RemapSelection()
{
ItemIndexRangeList oldSelection = selection;
ItemCacheManager<string> oldSelectionCache = selectionCache;
ItemIndexRangeList newSelection = new ItemIndexRangeList();
ItemCacheManager<string> newSelectionCache = new ItemCacheManager<string>(fetchSelectionDataCallback, 50, "newSelectionCache");
foreach (ItemIndexRange r in oldSelection)
{
IReadOnlyList<StorageFile> results = null;
int lastResultOffset = 0, lastResultsItemIndex = 0;
for (int i = 0; i < r.Length; i++)
{
int origIndex = r.FirstIndex + i;
string fileid = oldSelectionCache[origIndex];
bool matched = false;
// Optimization to be able to work in batches. Once we get a batch of files from the filesystem we use that to hunt
// for matches rather than having to go ask for the index of each file
if (results != null)
{
for (int j = lastResultOffset + 1; j < results.Count; j++)
{
if (results[j].FolderRelativeId == fileid)
{
lastResultOffset = j;
int itemIndex = lastResultsItemIndex + j;
newSelection.Add((uint)itemIndex, 1);
newSelectionCache[itemIndex] = oldSelectionCache[origIndex];
matched = true;
break;
}
}
}
if (!matched)
{
// Get a starting point for the index of the file
lastResultsItemIndex = (int)(await _queryResult.FindStartIndexAsync(fileid.Substring(fileid.LastIndexOf('\\') + 1)));
lastResultOffset = 0;
// Get the files at that point and see if the keys actually match
results = await _queryResult.GetFilesAsync((uint)lastResultsItemIndex, 50);
if (results[lastResultOffset].FolderRelativeId == fileid)
{
newSelection.Add((uint)lastResultsItemIndex, 1);
newSelectionCache[lastResultsItemIndex] = oldSelectionCache[origIndex];
}
else
{
// We can't find the item, so its no longer part of the selection
}
}
}
}
// Update the fields for the new selection
selection = newSelection;
selectionCache = newSelectionCache;
}
// Handles a change notification for the list of files from the OS
private void ResetCollection()
{
// Unhook the old change notification
if (itemCache != null)
{
this.itemCache.CacheChanged -= ItemCache_CacheChanged;
}
// Create a new instance of the cache manager
this.itemCache = new ItemCacheManager<FileItem>(fetchDataCallback, 50);
this.itemCache.CacheChanged += ItemCache_CacheChanged;
if (CollectionChanged != null)
{
CollectionChanged(this, new NotifyCollectionChangedEventArgs(NotifyCollectionChangedAction.Reset));
}
}
