I know userAgent using Dropbox's account

I'm afraid I don't understand your question.

It sounds like you're using Xamarin library though. That's not made by Dropbox, so I recommend referring to the documentation for that library for information.

Hi, Greg K.

I'm sorry that I'm not acquiring English.

I'm read under link.
https://www.dropbox.com/developers/documentation/dotnet

It's sample is very good!!!
(I know that Xamarin's download method is buggy.)

But, I want to use that user login, it's not debelloper's folder.

So, I read Documentation. But I don't understand user login.
http://dropbox.github.io/dropbox-sdk-dotnet/html/R_Project_DotNetApiDocumentation.htm

So, I want to know Dropbox API .

Maybe, is there a wrong place to ask questions about this page's API?

If so, are you not able to tell me where your questions are?

Thank you for reading and reply.

Thanks for following up. This is a good place to ask questions about the API.

It sounds like you want to implement the app authorization flow in your app so that arbitrary end-users can connect their own Dropbox accounts to it.

To do so, you will need to use the OAuth 2 app authorization flow. (You can find some general information on how that works in the OAuth Guide.)

In the official Dropbox API v2 .NET SDK, there is a DropboxOAuth2Helper class that does a lof of the work for you. The documentation there has more information. The SDK also comes with a number of examples that show how to use that.