Licensing iPhone software by "number of items supported"

Let's say that I have an application that helps people "manage" a certain number of "items". Normally they'd have to manage information about these items on paper, but my application will let 开发者_如何学JAVAthem do it on the phone.

I want to sell my application by the number of items it supports. For example, I might charge $10 for the version that has a limit of 20 items, and $15 for the version that lets you manage 40 items.

What's the best way to do this? Ideally I'd like to let users download the application for free as a sort of trial that only supports a very small number of items like 2 or 3, then they'd have to use in-app purchases or something to buy additional capacity.

I also need them to be able to "re-download" their license from the app store if they wipe their phone or it gets destroyed.

I also want people to be able to buy upgrades as they go along. So once they find they need to manage more than 20 items or whatever, I want them to be able to buy an upgrade for 40 without having to reinstall the app or something.

Installing extra application bundles for each license or license upgrade seems like a bad way to do things, though I'm sure I could have them all use the same bundle seed ID and have them insert license info into the keychain or something.

Anyway, ideas?

You could use in-app purchase to add extra “items” to the user’s list. That will survive a phone restore and you could support adding as many “items” as possible.

I think the best way is to manage this via some sort of subscription where the 'items' are stored on your server rather than the phone. Then you can control the number of them and use the app to access each item.

So, you run the app, it manages these 'items' and each item is stored on your backend database. Depending on their subscription, you can allow/deny attempts to add items.

Alternatively, I guess you could do a similar thing on the iPhone using the built in database but you'll still need a backend somewhere to keep control of the number of items they can manage, whether that's via some sort of certificate or whatever.