How to find out that the user has installed the application under the iPhone / iPad programmatically?

Question

iOS

It is planned to release several paid apps for iPhone/iPad and one free one that will show which of these paid apps are already installed.
Is it possible to do this? And where can I read about it.
Thank you.

Answer 1

Can. In iOS4, apps can support so-called URL schemes. For an app, you can set several URL schemes, for example, “aaa” will look like this: aaa://something
So, for all your paid applications, make support for at least one scheme, each app has a different scheme (for example aaa, bbb, ccc). And in the free one, check if the system supports URL schemes (aaa, bbb, ccc). This is done through:
- (BOOL)canOpenURL:(NSURL *)url
It seems that everything is done like this.

Answer 2

And sewing up a free mandatory activation of the application online is not an option?