OS&Swift-UI ViewControllerライフサイクルの学習(英語)

viewWillAppear

override func viewDidLoad() {
	super.viewDidLoad() 
}

Called when content view created in memory

What is content view?

→ When you create a new view controller (cocoatoach class) in your storyboard, a View object is created automatically. The content view aforementioned is this.
viewWillAppear

override func viewWillAppear(_ animated: Bool){
	super.viewWillAppear(animated)
}

Called just before content view is added to app's view hierarchy

→ Doesn't necessarily mean that it will "appear"in the screen as you can call view.isHidden = true sometimes.
→ This method is called everytime we come back to the View Controller.
→ viewDidLoad only gets called once because it is called when it is stacked in the navigation controller memory.
viewDidAppear

override func viewDidAppear(_ animated: Bool){
	super.viewDidAppear(animated)
}

Called after the content view is added to app's view hierarchy

→ You might want to configure animations in this method. Animations might start a little bit too soon if you put animation related code in viewWillAppear or viewDidLoad.
viewWillDisappear

override func viewWillDisappear(_ animated: Bool){
	super.viewWillDisappear(animated)
}

Called before the content view is removed from the app's view hierarchy

→ Often used when you want to save some sort of data right before the user dismisses the view.
viewDidDisappear

override func viewDidDisappear(_ animated: Bool){
	super.viewDidDisappear(animated)
}

Called after the content view is removed from the app's view hierarchy