通过 Calendar 计算今年几岁？

Calendar.swift

/// 计算今年年龄 eg: 1992-03-19
func calculateThisYearAge(birthday: String) -> Int?{
    let dateFormatter = DateFormatter()
    dateFormatter.dateFormat = "yyyy-MM-dd"
    if let birthday = dateFormatter.date(from: birthday) {
        let gregorian = Calendar(identifier: .gregorian)
        let components = gregorian.dateComponents([Calendar.Component.year], from: birthday, to: Date())
        if let year =  components.year {
            return year + 1
        }
    }
    return nil
}