Time limited Shareware

I'm thinking about making a time limited full version o开发者_如何学Gof my App, so users can try it for example 7 days.

Is there a recommended Obj-C library?

First of all do not store your data inside the app. Otherwise it would be simple to delete the App from the filesystem and download it again restarting the countdown. Store it in User preferences or Application Support instead. You could use a plist for this. You could also use a hidden file if you like. Just don't make it too complicated or too invasive. Your app can be cracked no matter what security measures you use in the end. Just be fair enough to the end user that could be a prospective customer.

Here is a very nice link on the topic of implementing a time-limited trial in Cocoa:

http://lipidity.com/apple/shareware-licensing-techniques/

Without possibility to protect your data from manipulation/deletion it is not possible to do.
How do yo check, if it is first start of your application, if all your data is wiped out.

Some alternative is "hardcoded" id token and connection to the rest of world (at least for first start, to grab any kind signed data key)

Maybe you could use a server where store UUID's and first time they launched the App. Then, Each time they open your application, it asks your server if they can use it or not. It's harder than store dates on device but if you do that, users will access your application simply changing the date of the device on Settings.