New DropBox Ui does not support the API ???

when i am trying to retrive user list in the past, i used this :

client.Team.MembersListAsync().ConfigureAwait(false);

but now it is different beacuse i am using the dropboxClient and not the dropboxTeamClient.

same question is about the groups and GetItemSecurityAsync.

how to i get them using the dropbox client?

How you call team methods, such as MembersListAsync and GroupsListAsync has not changed. These continue to be available on DropboxTeamClient only, not DropboxClient.

I don't know what you're referring to by "GetItemSecurityAsync" though, as that doesn't seem to be a method in the .NET SDK.

is there a way to use in the team space like in the older version with AsMember() or

AsAdmin.

The "member file access" feature continues to be available for both configurations, in the .NET SDK via DropboxTeamClient.AsAdmin and DropboxTeamClient.AsMember. These methods allow you to perform actions on behalf of specific admins or members, whether or not the team happens to be using the team space configuration.

when is dropbox planning to leave the old UI or it is somthing that will stay for a long time?

I can't offer a timeline for when the different configurations may be in use. I can only offer help with the Dropbox API itself. You may wish to contact Dropbox Business support for general questions about Dropbox Business itself. 

do i need to user both ? or how can i use both ?

This depends on your app and who will be using it. If your app is meant for use by any arbitrary Dropbox Business team, I recommend supporting both configurations. If it is only meant for your own use or use by specific team(s), you can build it just for whichever configuration(s) are needed.

it there a different way to contact you for help?

We offer a variety of channels for getting help for the Dropbox API, but note that they are all handled by the same Dropbox developer support department and so help will be given at about the same rate across the channels. You can contact Dropbox Business support for general questions about Dropbox Business itself.