public Task ExportAsync(CancellationToken cancellationToken, Action <int> reportProgress)
{
this.cancellationToken = cancellationToken;
this.ReportProgress = reportProgress ?? delegate { };
tcs = new TaskCompletionSource <bool>();
writer = new CsvWriter(stream);
extractor = new DocumentColumnsExtractor(columns);
writer.WriteHeaderRecord(columns.Select(c => c.Header));
FetchNextPage();
return(tcs.Task);
}
public async Task ExportAsync(CancellationToken cancellationToken, Action <int> reportProgress)
{
reportProgress = reportProgress ?? delegate { };
var context = SynchronizationContext.Current;
using (stream)
using (var writer = new CsvWriter(stream))
{
var extractor = new DocumentColumnsExtractor(columns);
writer.WriteHeaderRecord(columns.Select(c => c.Header));
// we do the streaming of documents on a background thread mainly to escape the
// SynchronizationContext: when there's no synchronization context involved the
// async methods can resume on any thread instead of having to hop back to the UI thread.
// This avoids massive overheads
await TaskEx.Run(async() =>
{
var totalResults = new Reference <long>();
using (var documentsStream = await collectionSource.StreamAsync(totalResults))
{
IList <JsonDocument> documentBatch;
var fetchedDocuments = 0;
do
{
documentBatch = await GetNextBatch(documentsStream, cancellationToken);
fetchedDocuments += documentBatch.Count;
// extracting properties from the documents has to be done on the UI thread
// because it might involve using FrameworkElements and Silverlight databinding
context.Send(delegate
{
WriteColumnsForDocuments(writer, documentBatch, extractor);
reportProgress((int)(((double)fetchedDocuments / totalResults.Value) * 100));
}, null);
} while (documentBatch.Count > 0);
}
}, cancellationToken);
}
}
private void WriteColumnsForDocuments(CsvWriter writer, IEnumerable <JsonDocument> documents, DocumentColumnsExtractor extractor)
{
foreach (var document in documents)
{
var values = extractor.GetValues(document);
writer.WriteDataRecord(values);
}
}
