public ItemCacheManager(FetchDataCallbackHandler <T> callback, int batchsize = 50)
{
_cacheBlocks = new List <CacheEntryBlock <T> >();
_request = new ItemIndexRangeList();
_cachedResults = new ItemIndexRangeList();
_fetchDataCallback = callback;
_maxBatchFetchSize = batchsize;
// set up a timer that is used to delay fetching data so that we can catch up if the list is scrolling fast
_timer = new DispatcherTimer();
_timer.Tick += (sender, args) => { FetchData(); };
_timer.Interval = new TimeSpan(20 * 10000);
}
/// <summary>
/// Updates the desired item range of the cache, discarding items that are not needed, and figuring out which items
/// need to be requested. It will then kick off a fetch if required.
/// </summary>
/// <param name="ranges">New set of ranges the cache should hold</param>
public void UpdateRanges(ItemIndexRange[] ranges)
{
// Normalize ranges to get a unique set of discontinuous ranges
ranges = NormalizeRanges(ranges);
// Fail fast if the ranges haven't changed
if (!HasRangesChanged(ranges))
{
return;
}
// To make the cache update easier, we'll create a new set of CacheEntryBlocks
List <CacheEntryBlock <T> > newCacheBlocks = new List <CacheEntryBlock <T> >();
foreach (ItemIndexRange range in ranges)
{
CacheEntryBlock <T> newBlock = new CacheEntryBlock <T>
{
FirstIndex = range.FirstIndex,
Length = range.Length,
Items = new T[range.Length]
};
newCacheBlocks.Add(newBlock);
}
// Copy over data to the new cache blocks from the old ones where there is overlap
int lastTransferred = 0;
for (int i = 0; i < ranges.Length; i++)
{
CacheEntryBlock <T> newBlock = newCacheBlocks[i];
ItemIndexRange range = ranges[i];
int j = lastTransferred;
while (j < _cacheBlocks.Count && _cacheBlocks[j].FirstIndex <= ranges[i].LastIndex)
{
ItemIndexRange overlap, oldEntryRange;
ItemIndexRange[] added, removed;
CacheEntryBlock <T> oldBlock = _cacheBlocks[j];
oldEntryRange = new ItemIndexRange(oldBlock.FirstIndex, oldBlock.Length);
bool hasOverlap = oldEntryRange.DiffRanges(range, out overlap, out removed, out added);
if (hasOverlap)
{
Array.Copy(oldBlock.Items, overlap.FirstIndex - oldBlock.FirstIndex, newBlock.Items, overlap.FirstIndex - range.FirstIndex, (int)overlap.Length);
}
j++;
if (ranges.Length > i + 1 && oldBlock.LastIndex < ranges[i + 1].FirstIndex)
{
lastTransferred = j;
}
}
}
// swap over to the new cache
_cacheBlocks = newCacheBlocks;
// figure out what items need to be fetched because we don't have them in the cache
_request = new ItemIndexRangeList(ranges);
ItemIndexRangeList newCachedResults = new ItemIndexRangeList();
// Use the previous knowlege of what we have cached to form the new list
foreach (ItemIndexRange range in ranges)
{
foreach (ItemIndexRange cached in _cachedResults)
{
ItemIndexRange overlap;
ItemIndexRange[] added, removed;
bool hasOverlap = cached.DiffRanges(range, out overlap, out removed, out added);
if (hasOverlap)
{
newCachedResults.Add(overlap);
}
}
}
// remove the data we know we have cached from the results
foreach (ItemIndexRange range in newCachedResults)
{
_request.Subtract(range);
}
_cachedResults = newCachedResults;
StartFetchData();
}
