discarded_notification_center_observer.md

Pattern: Discarded NotificationCenter observer

Issue: -

Description

When registering for a notification using a block, the opaque observer that is returned should be stored so it can be removed later.

Examples of correct code:

let foo = nc.addObserver(forName: .NSSystemTimeZoneDidChange, object: nil, queue: nil) { }


let foo = nc.addObserver(forName: .NSSystemTimeZoneDidChange, object: nil, queue: nil, using: { })


func foo() -> Any {
   return nc.addObserver(forName: .NSSystemTimeZoneDidChange, object: nil, queue: nil, using: { })
}

Examples of incorrect code:

↓nc.addObserver(forName: .NSSystemTimeZoneDidChange, object: nil, queue: nil) { }


↓nc.addObserver(forName: .NSSystemTimeZoneDidChange, object: nil, queue: nil, using: { })


@discardableResult func foo() -> Any {
   return ↓nc.addObserver(forName: .NSSystemTimeZoneDidChange, object: nil, queue: nil, using: { })
}

Further Reading

• SwiftLint - Discarded Notification Center Observer