how to use session in iphone programming?

I made an iphone story book application. Suppose any user read story book and at half of the story book he/she close the apps. when he/she want to read again this application at a time ask for continue or start again. This is possible by using session but i don't know how to use session in iphone sdk. So, please help me about thi开发者_如何学Gos problem.

Thanks!

You have to do it more or less manually. One way to do it is to write to NSUserDefaults in your ApplicationWillTerminate: method of your app delegate, and then to load in ApplicationDidFinishLaunching: