iOS Label text 自動改變大小 dynamic type

字體大小對照表

https://codershigh.github.io/guidelines/ios/human-interface-guidelines/visual-design/typography/index.html#

Label

1.

2.

3.

iOS 10

label.font = UIFont.preferredFont(forTextStyle: .body)

label.adjustsFontForContentSizeCategory = true

4.

自訂字體（iOS 11才有）

let customFont = UIFont.systemFont(ofSize: 20)

label.font = UIFontMetrics.default.scaledFont(for: customFont)
label.adjustsFontForContentSizeCategory = true

Xcode 快速驗證 

取得現在字體大小
UIApplication.shared.preferredContentSizeCategory

修改字體大小的Notification
UIContentSizeCategory.didChangeNotification