.NET C# - Check and download/Sync missing files with local files

[Cross-linking for reference: https://stackoverflow.com/questions/52625933/net-c-sharp-check-and-download-sync-missing-files-with-local-files-using-drop ]

"use the file size as a reference?"

I do not recommend using size, as that can result in false positives. That is, two files can have the same size but different contents.

"How can i check if a specific file has been modified in the dropbox directory comparing it with the local files(If it hjas been downloaded before)?"

One way to do this would be to record which "rev" you downloaded, that is, the FileMetadata.Rev, included with the file download. When you check again later (e.g., from GetMetadata or ListFolder[Continue]), if the rev hasn't changed, you know you still have the latest copy. If the rev has changed, the file data may have changed.

Alternatively, you can check the FileMetadata.ContentHash. That can directly indicate if you have the same file data. You can find information on how that works here.

"How can i download the file asynchronously to the same local folder?"

You can use the DownloadAsync method to download files, as seen in the examples here and here. What you do with the file data is up to you. For instance, unlike those examples, it sounds like you want to save the data to the local filesystem.

"How can i implement a progress bar showing the file name AND the progress in percent(0-100)?"

The Dropbox API v2 .NET SDK does not offer progress listeners, but I'll be sure to pass this along as feedback. You can track progress from the download stream itself though as shown in this thread.