In App Purchase with restore transaction

Can anyone please explain me how restore transaction works with Auto-Renewable Subscriptions.

I have read apple http://developer.apple.com/library/ios/#documentation/NetworkingInternet/Conceptual/StoreKitGuide/RenewableSubscriptions/RenewableSubscriptions.html#//apple_ref/doc/uid/TP40008267-CH4-SW5 But did not get this.

I have an application which does not have Login authentication. If user purchase the Product from one device and same user install the app on another device how can i know that the user who installed the app has alread开发者_如何学Pythony purchase the product.

if user goes to purchase the product they already purchase is there any delegate methods for it that we can know that is user has already purchase the product.

Thanks.

You no need to worry about the transaction. For such user, when he tries to purchase the item, store will inform him that he has already purchased the particular item. So he can download it for free.