👓 Observer Pattern
Tags: swift, programming, computerscience, architecture
Published: 2022-12-13 17:32:27


![Observer Pattern](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/y7axhp6bxvrrnreeu0fp.png)

---

The observer pattern is used to allow an object to publish changes to its state. Other objects subscribe to be immediately notified of any changes.

Github https://github.com/sergeyleschev/design-patterns

**Example**
```swift
protocol PropertyObserver : class {
    func willChange(propertyName: String, newPropertyValue: Any?)
    func didChange(propertyName: String, oldPropertyValue: Any?)
}

final class TestChambers {
    weak var observer:PropertyObserver?

    private let testChamberNumberName = "testChamberNumber"

    var testChamberNumber: Int = 0 {
        willSet(newValue) {
            observer?.willChange(propertyName: testChamberNumberName, newPropertyValue: newValue)
        }
        didSet {
            observer?.didChange(propertyName: testChamberNumberName, oldPropertyValue: oldValue)
        }
    }
}

final class Observer : PropertyObserver {
    func willChange(propertyName: String, newPropertyValue: Any?) {
        if newPropertyValue as? Int == 1 {
            print("Okay. Look.")
        }
    }

    func didChange(propertyName: String, oldPropertyValue: Any?) {
        if oldPropertyValue as? Int == 0 {
            print("Sorry about the mess.")
        }
    }
}
```
**Usage**
```swift
var observerInstance = Observer()
var testChambers = TestChambers()
testChambers.observer = observerInstance
testChambers.testChamberNumber += 1
```
Sources: [Github](https://github.com/sergeyleschev/design-patterns/tree/main/Observer)
> **_Behavioral_**
In software engineering, behavioral design patterns are design patterns that identify common communication patterns between objects and realize these patterns. By doing so, these patterns increase flexibility in carrying out this communication.
Source: [wikipedia.org](https://en.wikipedia.org/wiki/Behavioral_pattern)

---

🐝 [Chain Of Responsibility](https://dev.to/sergeyleschev/swift-design-patterns-chain-of-responsibility-4bbd)
👫 [Command Pattern](https://dev.to/sergeyleschev/swift-design-patterns-command-pattern-3044)
🎶 [Interpreter Pattern](https://dev.to/sergeyleschev/swift-design-patterns-interpreter-pattern-390a)
🍫 [Iterator Pattern](https://dev.to/sergeyleschev/swift-design-patterns-iterator-pattern-405o)
💐 [Mediator Pattern](https://dev.to/sergeyleschev/swift-design-patterns-mediator-pattern-4299)
💾 [Memento Pattern](https://dev.to/sergeyleschev/swift-design-patterns-memento-pattern-chp)
👓 [Observer Pattern](https://dev.to/sergeyleschev/swift-design-patterns-observer-pattern-44fc)
🐉 [State Pattern](https://dev.to/sergeyleschev/swift-design-patterns-state-pattern-5ej4)
💡 [Strategy Pattern](https://dev.to/sergeyleschev/swift-design-patterns-strategy-pattern-143c)
📝 [Template Method](https://dev.to/sergeyleschev/swift-design-patterns-template-method-1c2o)
🏃 [Visitor Pattern](https://dev.to/sergeyleschev/swift-design-patterns-visitor-pattern-4hl5)
🌰 [Abstract Factory](https://dev.to/sergeyleschev/swift-design-patterns-abstract-factory-3ppa)
👷 [Builder Pattern](https://dev.to/sergeyleschev/swift-design-patterns-builder-pattern-3609)
🏭 [Factory Method](https://dev.to/sergeyleschev/swift-design-patterns-factory-method-5c6e)
🔂 [Monostate Pattern](https://dev.to/sergeyleschev/swift-design-patterns-monostate-pattern-574i)
🃏 [Prototype Pattern](https://dev.to/sergeyleschev/swift-design-patterns-prototype-pattern-n25)
💍 [Singleton](https://dev.to/sergeyleschev/swift-design-patterns-singleton-3c8b)
🔌 [Adapter Pattern](https://dev.to/sergeyleschev/swift-design-patterns-adapter-pattern-1040)
🌉 [Bridge Pattern](https://dev.to/sergeyleschev/swift-design-patterns-bridge-pattern-1ee2)
🌿 [Composite Pattern](https://dev.to/sergeyleschev/swift-design-patterns-composite-pattern-1koj)
🍧 [Decorator Pattern](https://dev.to/sergeyleschev/swift-design-patterns-decorator-pattern-2c6p)
🎁 [Facade Pattern](https://dev.to/sergeyleschev/swift-design-patterns-facade-pattern-130a)
🍃 [Flyweight Pattern](https://dev.to/sergeyleschev/swift-design-patterns-flyweight-pattern-6ko)
☔ [Protection Proxy](https://dev.to/sergeyleschev/swift-design-patterns-protection-proxy-3kpc)
🍬 [Virtual Proxy](https://dev.to/sergeyleschev/swift-design-patterns-virtual-proxy-2bbg)

---

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