我将获取日期的月和日的日期组件，并对这些值进行简单的比较

let components = Calendar.current.dateComponents([.month, .day], from: date)
let inPeriod = (components.month! == 12 && components.day! >= 15) || (components.month! == 1 && components.day! <= 15)

简单测试用例

var testDate = Calendar.current.date(from: DateComponents(calendar: .current, year: 2021, month: 12, day: 14))!

for _ in 1...34 {
    let components = Calendar.current.dateComponents([.month, .day], from: testDate)
    print(testDate, (components.month! == 12 && components.day! >= 15) || (components.month! == 1 && components.day! <= 15))
    testDate = Calendar.current.date(byAdding: .day, value: 1, to: testDate)!
}

您不能忽略年份，尤其是当年份的转折点在区间内时。由于实际上涉及到当前日期，您希望检查该日期是否在当前年的12月和下年的1月之间
我的建议是从当前日期获取年组件，然后通过将月设置为12、日设置为15来构建开始日期，并通过向指向下一年1月16日的开始日期添加一天和一个月来构建结束日期。

let currentDate = Date.now
let year = Calendar.current.component(.year, from: currentDate)
let startComponents = DateComponents(year: year, month: 12, day: 15)
let startDate = Calendar.current.date(from: startComponents)!
let endDate = Calendar.current.date(byAdding: DateComponents(month: 1, day: 1), to: startDate)!

if currentDate >= startDate && currentDate < endDate {
    print("isValid")
}

我要赎罪！
1.没有看到您正在寻找一个考虑到您所在时区的解决方案
1.没看到你想要的东西只对间隔感兴趣，而不是在年。
我得承认，有时候我看书时没有注意到问题，特别是那些我认为很容易的问题。
希望下面的解决方案能满足你的需要。就像其他学院说的，你不可能不考虑年份，但是你可以像你一样在函数里面模拟年份。
请自己看一看，看看您是更喜欢我的解决方案，还是坚持使用您的解决方案：

import Foundation

let f = ISO8601DateFormatter()
f.formatOptions = .withFullDate
f.timeZone = TimeZone(abbreviation: "PST")

func thisDate(_ date: Date, isBetweenthisMonth initialMonth: Int, andDay initialDay: Int, andThisOtherMonth finalMonth: Int, andThisOtherDay finalDay: Int) -> Bool {
    var isBetween = false
    
    let year = Calendar.current.component(.year, from: date)
    
    let initialYear = year
    var finalYear = year
    
    if finalMonth < initialMonth {
        finalYear += finalYear
    }
    
    let initialFakeData = f.date(from: "\(initialYear)-\(initialMonth)-\(initialDay)")!
    let finalFakeData = f.date(from: "\(finalYear)-\(finalMonth)-\(finalDay)")!
    
    if (date > initialFakeData && date < finalFakeData) {
        isBetween = true
    }
    
    return isBetween
}

// Some test cases to pass
let date = f.date(from: "2022-11-01")!

print(thisDate(date, isBetweenthisMonth: 12, andDay: 02, andThisOtherMonth: 02, andThisOtherDay: 23) == false ? "False" : "Something wrong.")
print(thisDate(date, isBetweenthisMonth: 10, andDay: 02, andThisOtherMonth: 01, andThisOtherDay: 15) == true ? "True" : "Something wrong.")

let date2 = f.date(from: "2022-12-31")!

print(thisDate(date2, isBetweenthisMonth: 12, andDay: 30, andThisOtherMonth: 01, andThisOtherDay: 01) == true ? "True" : "Something wrong.")
print(thisDate(date2, isBetweenthisMonth: 01, andDay: 01, andThisOtherMonth: 01, andThisOtherDay: 15) == false ? "False" : "Something wrong.")

let date_now = f.date(from: f.string(from: Date()))!

print(thisDate(date_now, isBetweenthisMonth: 11, andDay: 08, andThisOtherMonth: 11, andThisOtherDay: 10) == true ? "True" : "Something wrong.")
print(thisDate(date_now, isBetweenthisMonth: 12, andDay: 01, andThisOtherMonth: 02, andThisOtherDay: 01) == false ? "False" : "Something wrong.")

我不知道如何使用XCTest进入游戏场，所以我在最后的代码中模拟了一些测试。