The OnlineUser Interface is the central repository for all cached information and metadata about users, both remote and local. This interface also provides reverse-lookup functionality, enabling developers to search for user IDs based on their display names or email addresses and map them back to Unreal Engine 4's native FUniqueId system.
Retrieving and Examining User Metadata
To access user metadata, you must first request and cache that data from the online service. Call QueryUserInfo with a list of FUniqueNetId values for the users whose information you want, as well as the index of the local user making the request. This is an asynchronous process, and will call a delegate of type OnQueryUserInfoComplete when it finishes. After a successful query populates the cache with user information, the GetAllUserInfo function will return all collected data. If you have the FUniqueNetId of a specific user whose data you want, you can call GetUserInfo with that FUniqueNetId to get just that user's data.
Mapping External User IDs
Most online services support searching for users by their display names or email addresses. The OnlineUser Interface mirrors this functionality with QueryUserIdMapping, which takes a display name or email address and attempts to map it, through the online service, to an FUniqueNetId. Since this procedure involves contacting the online service, it is asynchronous, and will call FOnQueryUserMappingComplete upon completion. Unlike most information requests, this function does not update a cache. Instead, when the operation is successful, the delegate's payload will contain the known display name or email address that was searched, and the resulting FUniqueNetId that the online service found.