How do I upload a file to my dropbox apps folder in dropbox in objective c?

Thanks. That's correct, you don't have to call the callback methods yourself, they get called by the SDK.

Also, note that the app key passed to initWithAppKey should be just the app key, without the "db-" prefix. The "db-" prefix is only necessary for the URL scheme you register in the plist.

Finally, yes, as you mentioned this error is expected as you're just initializing an empty DBAccount object, so the userId isn't set. 

Normally, you don't need to know the user ID to start with, as the user authorizes the account, and doesn't supply an access token themselves. It is possible to use API/SDK like this with a single account, but it isn't recommended, for a variety of security and technical reasons.

If you do go this route though, you'll need to get the user ID for your account once, just like you got an access token for your account once. You can do this by calling the /account/info endpoint manually once. This blog post covers how to make these calls with OAuth 1 manually if you need.