private void FetchNextPage()
{
collectionSource.GetPageAsync(fetchedDocuments, PageSize, null).ContinueOnUIThread(t =>
{
if (cancellationToken.IsCancellationRequested)
{
tcs.SetCanceled();
CleanUp();
return;
}
if (!t.IsFaulted)
{
WriteColumnsForDocuments(writer, t.Result, extractor);
fetchedDocuments += t.Result.Count;
ReportProgress((int)(((double)fetchedDocuments / collectionSource.Count) * 100));
if (fetchedDocuments < collectionSource.Count)
{
FetchNextPage();
}
else
{
tcs.SetResult(true);
CleanUp();
}
}
else
{
tcs.SetException(t.Exception);
CleanUp();
}
});
}
private void ProcessPageRequests()
{
while (_inProcessPageRequests < MaxConcurrentPageRequests && _pendingPageRequests.Count > 0)
{
var request = _pendingPageRequests.Pop();
// if we encounter a requested posted for an early collection state,
// we can ignore it, and all that came before it
if (State != request.StateWhenRequested)
{
_pendingPageRequests.Clear();
break;
}
// check that the page is still requested (the user might have scrolled, causing the
// page to be ejected from the cache
if (!_requestedPages.Contains(request.Page))
{
break;
}
_inProcessPageRequests++;
var tsk = _source.GetPageAsync(request.Page * _pageSize, _pageSize, _sortDescriptions);
tsk.ContinueWith(
t =>
{
if (!t.IsFaulted)
{
UpdatePage(request.Page, t.Result, request.StateWhenRequested, request.PreviousNextRequest);
}
else
{
MarkPageAsError(request.Page, request.StateWhenRequested);
}
// fire off any further requests
_inProcessPageRequests--;
ProcessPageRequests();
}, _synchronizationContextScheduler);
tsk.Start();
}
}
