Swift KVO introduction

1. KVO
Jintin

2. Agenda
• Observer Pattern
• What is KVO
• KVO in Swift 4

3. How to dispatch
Information ?

4. Hollywood Principle

5. Observer Pattern

6. Observer Pattern
• Event Driven
• Easy to write
• Decoupling

7. Observer Pattern
Observer Subject
Register / Unregister
Notify

8. KVO

9. KVO
• Key Value Observing
• informal
• define in NSKeyValueObserving
• implement in NSObject
• Base on Objective-C runtime

10. implementation
// Add Observer
addObserver(_:forKeyPath:options:context:)
// Wait Callback
observeValue(forKeyPath:of:change:context:)
// Remove Observer
removeObserver(_:forKeyPath:)

11. Trouble Shoot
• inherit from NSObject (NSKeyValueObserving)
• Data should add `dynamic` (Objective-C runtime)
• KeyPath wrong

12. Pros & Cons
• Easy to write
• Less code
• Decouple
• ….
• Hard to debug
• Hard to maintain
• Leak
• ….

13. new in Swift 4
• Still inherit from NSObject
• Use closure instead of callback function
• No need to remove Observer
• More like Swift

14. new in Swift 4
@objcMembers class Foo: NSObject {
dynamic var value: String = ""
}
let foo = Foo()
let observation = foo.observe(.value) { (foo, change) in
print("value: (foo.value)")
}

15. Q&A