一. 官方方法
DateComponents
A date or time specified in terms of units (such as year, month, day, hour, and minute) to be evaluated in a calendar system and time zone.
以要在日历系统和时区中计算的单位（例如年、月、日、小时和分钟）指定的日期或时间。
二. 实现
1. 计算两个字符串形式的日期的天数差
func dateDiff() -> Int {
// 计算两个日期差，返回相差天数
let formatter = DateFormatter()
let calendar = Calendar.current
formatter.dateFormat = "yyyy-MM-dd"
let today = Date()
// 开始日期
let startDate = formatter.date(from: "2021-06-08")
// 结束日期
let endDate = formatter.date(from: "2021-06-09")
let diff:DateComponents = calendar.dateComponents([.day], from: startDate!, to: endDate!)
return diff.day!
}
2. 计算当天跟某一天的天数差
func checkDiff() -> Int {
// 计算两个日期差，返回相差天数
let formatter = DateFormatter()
let calendar = Calendar.current
formatter.dateFormat = "yyyy-MM-dd"
// 当天
let today = Date()
let startDate = formatter.date(from: formatter.string(from: today))
// 固定日期
let endDate = formatter.date(from: "2021-06-09")
let diff:DateComponents = calendar.dateComponents([.day], from: startDate!, to: endDate!)
return diff.day!
}
