ASP.NET 顯示農曆時間：ChineseLunisolarCalendar 直接使用版

前言：內建行曆類別快速上手

.NET Framework 內建 System.Globalization.ChineseLunisolarCalendar 類別，無需第三方套件即可將公曆轉換為農曆（含年、月、日、干支、閏月）。本文提供可直接貼上頁面的完整代碼，適合快速原型、單頁腳本、教學示範。

完整代碼 (代碼後置 .aspx.cs)

using System;
using System.Globalization;
using System.Text;

public partial class LunarDemo : System.Web.UI.Page
{
    public string ChineseTimeNow = "";
    public string ForeignTimeNow = "";

    private static readonly ChineseLunisolarCalendar Calendar = new ChineseLunisolarCalendar();
    private const string ChineseNumber = "〇一二三四五六七八九";
    private const string CelestialStem = "甲乙丙丁戊己庚辛壬癸";
    private const string TerrestrialBranch = "子丑寅卯辰巳午未申酉戌亥";

    private static readonly string[] ChineseDayName = {
        "初一","初二","初三","初四","初五","初六","初七","初八","初九","初十",
        "十一","十二","十三","十四","十五","十六","十七","十八","十九","二十",
        "廿一","廿二","廿三","廿四","廿五","廿六","廿七","廿八","廿九","三十"
    };
    private static readonly string[] ChineseMonthName = {
        "正", "二", "三", "四", "五", "六", "七", "八", "九", "十", "十一", "十二"
    };

    protected void Page_Load(object sender, EventArgs e)
    {
        ChineseTimeNow = GetChineseDate(DateTime.Now);
        ForeignTimeNow = DateTime.Now.GetDateTimeFormats('D')[0].ToString();
    }

    public string GetChineseDate(DateTime time)
    {
        return $"{GetYear(time)}({GetStemBranch(time)})年 {GetMonth(time)}月 {GetDay(time)}";
    }
    public string GetStemBranch(DateTime time)
    {
        int y = Calendar.GetSexagenaryYear(time);
        return $"{CelestialStem[y % 10 - 1]}{TerrestrialBranch[y % 12 - 1]}";
    }
    public string GetYear(DateTime time)
    {
        int y = Calendar.GetYear(time);
        var sb = new StringBuilder();
        do { sb.Insert(0, ChineseNumber[y % 10]); y /= 10; } while (y > 0);
        return sb.ToString();
    }
    public string GetMonth(DateTime time)
    {
        int m = Calendar.GetMonth(time);
        int y = Calendar.GetYear(time);
        int leap = 0;
        for (int i = 3; i <= m; i++)
            if (Calendar.IsLeapMonth(y, i)) { leap = i; break; }
        if (leap > 0) m--;
        return (leap == m + 1 ? "閏" : "") + ChineseMonthName[m - 1];
    }
    public string GetDay(DateTime time) =>
        ChineseDayName[Calendar.GetDayOfMonth(time) - 1];
}

前台 .aspx 顯示

<table>
  <tr><td><%= ForeignTimeNow %></td></tr>
  <tr><td><%= ChineseTimeNow %></td></tr>
</table>

關鍵點說明

1. ChineseLunisolarCalendar 僅支援 1901-2100 年範圍，超出會拋出 ArgumentOutOfRangeException。
2. 干支計算：GetSexagenaryYear 回傳 1-60，對應十天干、十二地支索引需 -1。
3. 閏月判斷：正月不會閏，從 3 月開始檢查 IsLeapMonth，找到後月份 -1 並標記「閏」。
4. 中文數字轉換：以 StringBuilder.Insert(0, char) 反向組裝，避免再反轉。

與封裝版差異

總結

直接在頁面類別中實作農曆轉換，零依賴、零配置、即寫即用。若專案需在多處顯示農曆、或需單元測試、或規劃打包成 NuGet 套件，請改用封裝版 CountryDate 元件。兩者核心演算法相同，差異在於架構層次與複用策略。