c#关于时间的问题

实践/后端/C#基础/19.C#中关于时间.md

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+>关于年的问题
+- DownList显示年，可根据当前的年份，具体代码
+  ```
+   public List<string> GetYears()
+        {
+            List<string> allYears = new List<string>();
+            var now = DateTime.Now;
+            int currentYear = now.Year;//2019
+            allYears.Add((currentYear - 3).ToString());//2016
+            allYears.Add((currentYear - 2).ToString());//2017
+            allYears.Add((currentYear - 1).ToString());//2018
+            allYears.Add(currentYear.ToString());//2019
+            allYears.Add((currentYear + 1).ToString());//2020
+            allYears.Add((currentYear + 2).ToString());//2021
+            allYears.Add((currentYear + 3).ToString());//2022
+            return allYears;
+        }
+  ```
+
+> 关于月的问题
+- DownList显示月。因为月是具体的24个月，可直接增添值
+```
+ public List<string> GetMonths()
+        {
+            List<string> allMonths = new List<string>();
+            allMonths.AddRange(new List<string> { "01","02","03","04","05","06","07","08","09","10","11","12"});
+            return allMonths;
+        }
+```
+
+> 关于天的问题
+- 因为每年的每个月的天数不确定，可以根据请求或者选择的年月进行显示天数
+```
+/// <summary>
+        /// 获取天
+        /// </summary>
+        /// <param name="year"></param>
+        /// <param name="month"></param>
+        /// <returns></returns>
+        public List<string> GetDays(string year, string month)
+        {
+            var result = new List<string>();
+
+            if(!string.IsNullOrEmpty(year) && !string.IsNullOrEmpty(month))
+            {
+                //拼接月和年 2019-04
+                string yearAndMonthStr = year + "-" + month;
+                //月初 2019-04-01
+                DateTime beginTime = DateTime.Parse(yearAndMonthStr + "-01");
+                DateTime endTime = DateTime.Parse(beginTime.AddMonths(1).AddDays(-1).ToShortDateString());
+                //月末
+                for (DateTime dt = beginTime; dt <= endTime; dt = dt.AddDays(1))
+                {
+                    result.Add(dt.Day.ToString());
+                }
+            }
+            
+            return result;
+        }
+```
+> 时间格式转换（12或者24小时）
+```
+string time = Convert.ToDateTime(date).ToString("yyyy-MM-dd HH:mm");//HH为24小时
+string time = Convert.ToDateTime(date).ToString("yyyy-MM-dd hh:mm");//hh为12小时
+
+```