How to redownload an in-App purchase application programmatically

I am able to implement in-App purchase successfully. I am also able to purchase a product through in - App purchase.I am storing purchase information in NSUserDefaluts.So if next time user tries to purchase same product again i am able to handle it locally.My problem is if a user deletes the application from the device,How do i handle the re-downloading of the application without charging for the same product again.I know that if an application has been deleted from the device having in App purchase it has to be downloaded again.Can anybody show a sample code for the same?

Thanks Aditya

Hi Thanks for a prompt reply.I have implemented the same as you have suggested.What i'm wondering is if i delete my app and install it again , i am asked to purchase it again.Do i have to pay again for the upgrade or is it handled from the apple server(i.e if i upgrade the same product again am i charged again?).Is there a way to know it was upgraded without asking to upgrade again?

Solution

The StoreKit api takes care of this and gives you, on request, a list of identifiers of the purchased items. Once you got those, it's up to you to re-download the products again(if not already bundled inside the app).

Excerpt from the StoreKit API help:

-(void)restoreCompletedTransactions

Asks the payment queue to restore previously completed purchases.

Your application calls this method to restore transactions that were previously finished so that you can process them again. For example, your application would use this to allow a user to unlock previously purchased content onto a new device.

When you create a new product to be sold in your store, you choose whether that product can be restored or not. See the In App Purchase Programming Guide for more information.

The payment queue will deliver a new transaction for each previously completed transaction that can be restored. Each transaction includes a copy of the original transaction.