Update UI from Parallel.ForEach

Here is one my list of possibilities, how to update UI from Parallel.ForEach.

First, and probably the best with IProgress:

private readonly IProgress<int> _recordCountProgress;
private readonly IProgress<string> _fileNameProgress;
...
Parallel.ForEach(Directory.EnumerateFiles(path, "*.*", SearchOption.AllDirectories), options, fileName =>
{
	RecordCount = Interlocked.Increment(ref _recordCount);
	if (RecordCount % progressStep == 0)
	{
		_fileNameProgress.Report(fileName);
		_recordCountProgress.Report(RecordCount);
	}
});
...
IProgress<int> recordCountProgress = new Progress<int>(NumberOfFilesProcessedIProgress);
IProgress<string> fileNameProgress = new Progress<string>(FileProcessedIProgress);

notice:

	if (RecordCount % progressStep == 0)

If there are only few files _recordCount will be always 0, because it is to fast, if there are too many files, without UI would be blocked.

Second with SynchronizationContext:

Parallel.ForEach(Directory.EnumerateFiles(path, "*.*", SearchOption.AllDirectories), options, fileName =>
{
	RecordCount = Interlocked.Increment(ref _recordCount);
	if (RecordCount % progressStep == 0)
	{
			_syncContext?.Post(_ =>
			{
				FileProcessed?.Invoke(this,
					new FilesProcessedSynchronizationContextEventArgs(fileName));
				NumberOfFilesProcessed?.Invoke(this,
					new RecordCountSynchronizationContextEventArgs(_recordCount));
			}, null);
	}
});

Same as previous, problem with the line:

	if (RecordCount % progressStep == 0)

Third with System.Threading.Timer:

CancellationTokenSource = cancellationTokenSource;
_timer = new System.Threading.Timer(_ =>
{
	if (_queue.TryDequeue(out string? fileName))
	{
		if (form.InvokeRequired)
		{
			form.BeginInvoke(() =>
			{
				FileProcessed?.Invoke(this, new FilesProcessedEventArgs(fileName));
				NumberOfFilesProcessed?.Invoke(this, new RecordCountEventArgs(_recordCount));
			});
		}
		else
		{
			FileProcessed?.Invoke(this, new FilesProcessedEventArgs(fileName));
			NumberOfFilesProcessed?.Invoke(this, new RecordCountEventArgs(_recordCount));
		}
	}
}, null, 0, 100);

Example download from here