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

I have the call back methods implemented in the same class like so.

(void)restClient:(DBRestClient *)client uploadedFile:(NSString *)destPath from:(NSString *)srcPath metadata:(DBMetadata *)metadata {
    NSLog(@"File uploaded successfully to path: %@", metadata.path);
}

 (void)restClient:(DBRestClient *)client uploadFileFailedWithError:(NSError *)error {
    NSLog(@"File upload failed with error: %@", error);  
}  

Though I have not called them anywhere in the program. I suppose that may not be necessary.

I tried to add the updateAcessToken method inside my didFinishLaunching method like this. I have my actual app key and app secret in my actual code. I just omitted them for security.

DBSession *dbSession = [[DBSession alloc]
                        initWithAppKey:@"db-myAppKey"
                        appSecret:@"myAppSecret"
                        root:kDBRootAppFolder]; // either kDBRootAppFolder or kDBRootDropbox

 [dbSession updateAccessToken:@"myAccessToken" accessTokenSecret:@"MyAppsAppSecret" forUserId:[[DBAccountInfo alloc] init].userId];

[DBSession setSharedSession:dbSession];  

Xcode gives me the error:

setObjectForKey: key cannot be nil

userID is nil which makes sense. How do I obtain the user ID that is associated with the account that my app was created on without having to bring up a formal dropbox login view when I run the app? I want to be logged into the account that my app was created on, and obtain the userID all in the back end. I don't want the user of the app to have any knowledge that this is going on.