Is there any way to detect from your app (without using any private api) to detect if the iPhone (iOS) user has iTunes Store signed in or not?
There is no way for you to detect if the user has signed into their account in the app store.
Is there a particular reason why you are looking for this functionality? Your app should not worry about this.
来源：https://stackoverflow.com/questions/29978794/detect-if-user-is-signed-in-in-the-itunes-store