How to handle username in Cocoa Touch? - iphone

Question

I have a login view controller that uses the php/mysql/POST function to verify if a user is authorized. Once authorized, they enter the application.
My question is, once they are in the application, how do I "grab" their username and use it to append to any data that they upload to my database while they are in my app?
I am assuming I append it to my current NSMutableData string that carries the text blocks that they upload, but how would I "grab" this username to append it?
Assuming I have two view controllers, "login" and "main", and the content is being uploaded on "main", how do I pass the username from the "login" view to the "main" view so that I can append it when the user hits the upload button (which resides on the main view)?
EDIT: Where I want this username retrieved is in the following:
-(IBAction)uploadImage:(id)sender {
NSLog(#"uploadImage");
//and for retrieval
NSUserDefaults *defaults = [NSUserDefaults standardUserDefaults];
NSString *authenticatedUsersName = [defaults objectForKey:#"username"];
NSMutableString *postString = [NSMutableString stringWithString:kPostURL];
[postString appendString:[NSString stringWithFormat:#"&%#=%#", kText, textField.text]];
[postString setString:[postString stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding]];

Answer 1

If you're not concerned with security of a username, why don't you store the username in NSUserDefaults upon successful authentication? You can do something like this....
//upon authentication...
NSUserDefault *defaults = [NSUserDefaults standardUserDefaults];
if ([defaults objectForKey:#"username"] == nil) //we haven't saved anything yet
[defaults setObject:authenticatedUsersName forKey:#"username"];
[defaults synchronize]; //saves the new defaults
//and for retrieval
NSUserDefaults *defaults = [NSUserDefaults standardUserDefaults];
NSString *authenticatedUsersName = [defaults objectForKey:#"username"];
I think this design gives you more flexibility so you can use the username across all view controllers in your app.
post re-edit
Why can't you just format the string somewhere in this function? Whats the exact post url format?
-(IBAction)uploadImage:(id)sender {
NSLog(#"uploadImage");
//and for retrieval
NSUserDefaults *defaults = [NSUserDefaults standardUserDefaults];
NSString *authenticatedUsersName = [defaults objectForKey:#"username"];
//MY CHANGES, CAN YOU DO EITHER OF THESE?
NSMutableString *postString = [NSMutableString stringWithString:[NSString stringWithFormat:#"%#-%#", kPostURL, authenticatedUsersName];
[postString appendString:[NSString stringWithFormat:#"&%#=%#&%#", kText, textField.text, authenticatedUsersName]];
[postString setString:[postString stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding]];
}

Answer 2

An alternative method of having globally available variables is to use a singleton class.
This is slightly more difficult than Convolution's solution using NSUserDefaults, but it suits some use cases better.
There is a good tutorial at the following location:
http://www.galloway.me.uk/tutorials/singleton-classes/