如何比较 C # 中的日期时间？

//Time compare.
private int CompareTime(string t1, string t2)
{
TimeSpan s1 = TimeSpan.Parse(t1);
TimeSpan s2 = TimeSpan.Parse(t2);
return s2.CompareTo(s1);
}

public static bool CompareDateTimes(this DateTime firstDate, DateTime secondDate)
{
return firstDate.Day == secondDate.Day && firstDate.Month == secondDate.Month && firstDate.Year == secondDate.Year;
}

在一般情况下 你需要比较 DateTimes和相同的 Kind:

if (date1.ToUniversalTime() < date2.ToUniversalTime())
Console.WriteLine("date1 is earlier than date2");

MSDN对 DateTime.Compare的解释(这也适用于 >、 <、 ==等操作员) :

为了确定 t1与 t2的关系，Compare 方法比较 T1和 t2的 Ticks 属性，但是 忽略他们的类属性。 在比较 DateTime 对象之前，请确保这些对象表示 在同一时区的时间。

因此，在处理以不同时区表示的 DateTimes时，一个简单的比较可能会产生意想不到的结果。

如果有两个看起来相同的 DateTime，但 Compare 或 Equals 没有返回您所期望的值，这就是如何比较它们的方法。

下面是一个精度为1毫秒的例子:

bool areSame = (date1 - date2) > TimeSpan.FromMilliseconds(1d);

下面是 Unity 环境中一个典型的简单示例

using UnityEngine;


public class Launch : MonoBehaviour
{
void Start()
{
Debug.Log("today " + System.DateTime.Now.ToString("MM/dd/yyyy"));


// don't allow the app to be run after June 10th
System.DateTime lastDay = new System.DateTime(2020, 6, 10);
System.DateTime today = System.DateTime.Now;


if (lastDay < today) {
Debug.Log("quit the app");
Application.Quit();
}
UnityEngine.SceneManagement.SceneManager.LoadScene("Welcome");
}
}

using System;
//
public enum TimeUnit : byte {
Unknown = 0x00, //
Nanosecond = 0x01, // ns, not available in DateTime
Millisecond = 0x02, // ms
Second = 0x04, // sec
Minute = 0x08, // min
Hour = 0x10, // h
Day = 0x20, // d
Month = 0x40, // M
Year = 0x80, // Y
AllDate = TimeUnit.Year | TimeUnit.Month | TimeUnit.Day,
AllTime = TimeUnit.Hour | TimeUnit.Minute | TimeUnit.Second,
UpToNanosecond = TimeUnit.Nanosecond | TimeUnit.Millisecond | TimeUnit.Second | TimeUnit.Minute | TimeUnit.Hour | TimeUnit.Day | TimeUnit.Month | TimeUnit.Year,
UpToMillisecond = TimeUnit.Millisecond | TimeUnit.Second | TimeUnit.Minute | TimeUnit.Hour | TimeUnit.Day | TimeUnit.Month | TimeUnit.Year,
UpToSecond = TimeUnit.Second | TimeUnit.Minute | TimeUnit.Hour | TimeUnit.Day | TimeUnit.Month | TimeUnit.Year,
UpToMinute = TimeUnit.Minute | TimeUnit.Hour | TimeUnit.Day | TimeUnit.Month | TimeUnit.Year,
UpToHour = TimeUnit.Hour | TimeUnit.Day | TimeUnit.Month | TimeUnit.Year,
UpToDay = TimeUnit.Day | TimeUnit.Month | TimeUnit.Year,
UpToMonth = TimeUnit.Month | TimeUnit.Year,
};
//
public static partial class DateTimeEx {
//
private static void _Compare( ref int result, int flags, TimeUnit tu, int a, int b ) {
var which = (int) tu;
if ( 0 != ( flags & which ) ) {
if ( a != b ) result |= which;
}
}
///<summary>Compare Dates. The returned TimeUnit will have one flag set for every different field. It will NOT indicate which date is bigger or smaller.</summary>
public static TimeUnit Compare( this DateTime a, DateTime b, TimeUnit unit ) {
int result = 0;
var flags = (int) unit;
//ompare( ref result, flags, TimeUnit.Nanosecond, a.Nano, b.Nanosecond );
_Compare( ref result, flags, TimeUnit.Millisecond, a.Millisecond, b.Millisecond );
_Compare( ref result, flags, TimeUnit.Second, a.Second, b.Second );
_Compare( ref result, flags, TimeUnit.Minute, a.Minute, b.Minute );
_Compare( ref result, flags, TimeUnit.Hour, a.Hour, b.Hour );
_Compare( ref result, flags, TimeUnit.Day, a.Day, b.Day );
_Compare( ref result, flags, TimeUnit.Month, a.Month, b.Month );
_Compare( ref result, flags, TimeUnit.Year, a.Year, b.Year );
return (TimeUnit) result;
}
}
public static class Tests {
//
private static void TestCompare() {
var test = DateTime.UtcNow;
var ts = test.ToUnixTimestamp( true );
var test2 = DateTimeEx.ToDateTime( ts, true );
var ok = 0 == DateTimeEx.Compare( test, test2, TimeUnit.UpToSecond );
Log.Assert( ok );
ts = test.ToUnixTimestamp( false );
test2 = DateTimeEx.ToDateTime( ts, false );
ok = 0 == DateTimeEx.Compare( test, test2, TimeUnit.UpToSecond );
Log.Assert( ok );
}
}