How can I make my iOS apps talk to each other?
I’ve got several iOS apps and I need them to be aware of each other. More precisely, I need to know whether there’s already one of my apps installed.

I thought about registering a custom URL scheme (something like `my-app-present://`), so that I could check whether the custom scheme is supported and if yes, I would know there’s already one of my apps on the device. But that doesn’t work, because the schemes are registered through `Info.plist` and the app registers the scheme before it has a chance to check for its existence. In other words, the check always succeeds.

Then I thought about creating a file in the temporary directory, but `NSTemporaryDirectory()` returns a folder inside the application sandbox, so that wouldn’t work either. I also thought about keychain, but again it looks like each application has strictly separate keychain on iOS.

I don’t want to go through the list of running apps and I don’t want to use networking. Do you know some other tricks?
How can I make my iOS apps talk to each other?
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I’ve got several iOS apps and I need them to be aware of each other. More precisely, I need to know whether there’s already one of my apps installed.

I thought about registering a custom URL scheme (something like `my-app-present://`), so that I could check whether the custom scheme is supported and if yes, I would know there’s already one of my apps on the device. But that doesn’t work, because the schemes are registered through `Info.plist` and the app registers the scheme before it has a chance to check for its existence. In other words, the check always succeeds.

Then I thought about creating a file in the temporary directory, but `NSTemporaryDirectory()` returns a folder inside the application sandbox, so that wouldn’t work either. I also thought about keychain, but again it looks like each application has strictly separate keychain on iOS.

I don’t want to go through the list of running apps and I don’t want to use networking. Do you know some other tricks?