View Lifecycle: A Quick Summary

Photo by Simon Berger on Unsplash

view did load, did love, did loathe.

Quick notes on the iOS View Life cycle based on the Apple docs

viewDidLoad()

• 📞 called only once !
• 📞 called when content view is created
• 👀 but it is not necessary that the content view is created when the view controller is instantiated for the first time
• 🥱 content view is lazily created!
• 🧰 USE CASE: additional setup
• 📋 Storyboard — outlets guaranteed to have valid values

viewWillAppear()

• 📞 called when content view is about to be added to the view hierarchy
• ⚠️ does NOT guarantee that the content view will be visible
• view could be hidden or obscured by other views
• 🧰 USE CASE: any operation before the content view is presented onscreen

viewDidAppear()

• 📞 called right after the content view is added to the view hierarchy
• ⚠️ does NOT guarantee that the content view will be visible
• view could be hidden or obscured by other views
• 🧰 USE CASE: any operation that needs to take place as soon as the view is presented onscreen
• eg) fetching data
• eg) showing an animation

viewWillDisappear()

• 📞 called when content view is about to be removed from the view hierarchy
• ⚠️ wont be called just because the content view has been obscured or hidden
• 🧰 USE CASE: clean up tasks 🧼
• eg) committing changes
• eg) resigning first responder status

viewDidDisappear()

• 📞 called right after the content view is removed from the view hierarchy
• ⚠️ wont be called just because the content view has been obscured or hidden
• 🧰 USE CASE: additional tear down activities ✂️

References:

https://developer.apple.com/library/archive/referencelibrary/GettingStarted/DevelopiOSAppsSwift/WorkWithViewControllers.html