NSDate，比较两个日期[重复]

使用NSDate比较两个日期是一种常见的操作，通过比较日期可以判断它们的先后顺序和是否相等。在iOS开发中，我们经常会遇到需要比较日期的场景，比如计算两个日期之间的天数差、判断某个日期是否在某个日期范围内等等。下面我们将介绍如何 ，并附上相关的示例代码。

swift
let dateFormatter = DateFormatter()
dateFormatter.dateFormat = "yyyy-MM-dd"
let date1 = dateFormatter.date(from: "2021-01-01")
let date2 = dateFormatter.date(from: "2022-01-01")
if let d1 = date1, let d2 = date2 {
    let result = d1.compare(d2)
    if result == .orderedAscending {
        print("日期1在日期2之前")
    } else if result == .orderedSame {
        print("日期1和日期2相等")
    } else if result == .orderedDescending {
        print("日期1在日期2之后")
    }
}

swift
let dateFormatter = DateFormatter()
dateFormatter.dateFormat = "yyyy-MM-dd"
let startDate = dateFormatter.date(from: "2021-01-01")
let endDate = dateFormatter.date(from: "2021-12-31")
let targetDate = dateFormatter.date(from: "2021-06-01")
if let start = startDate, let end = endDate, let target = targetDate {
    let result1 = target.compare(start)
    let result2 = target.compare(end)
    if result1 == .orderedDescending && result2 == .orderedAscending {
        print("目标日期在指定日期范围内")
    } else {
        print("目标日期不在指定日期范围内")
    }
}

swift
let dateFormatter = DateFormatter()
dateFormatter.dateFormat = "yyyy-MM-dd"
let startDate = dateFormatter.date(from: "2021-01-01")
let endDate = dateFormatter.date(from: "2021-12-31")
if let start = startDate, let end = endDate {
    let timeInterval = end.timeIntervalSince(start)
    let days = Int(timeInterval / (24 * 60 * 60))
    print("两个日期之间相差\(days)天")
}