如何在swift 3.0中获得给定UIfont的可用大小列表

Question

IOS 10.x Swift 3.0

有这个代码列出可用的字体，效果很好。但是也想要尺寸，就像你在这样的面板中看到的那样......

var fontFamilies = UIFont.familyNames as [String]
var fontNames = [String]()
var fontSizes = [String]()

func listFonts() {
    for  i in 0 ..< fontFamilies.count {
        let fontFamily: NSString = fontFamilies[i] as NSString
        let localFontNames = UIFont.fontNames(forFamilyName: fontFamilies[i]) as [String]
        saveFont(fontNames: localFontNames)
    }
    NSLog ("%@:", fontNames)
}

但我想知道可用的尺寸，字体书从哪里获取这些信息？