csharp-datetime

发表于 2020-06-19 更新于 2022-11-19 分类于 Language 阅读次数：本文字数： 5.4k 阅读时长 ≈ 5 分钟

初始化

DateTime now = DateTime.Now;

获取时间

/获取日期+时间
DateTime.Now.ToString();            // 2008-9-4 20:02:10
DateTime.Now.ToLocalTime().ToString();        // 2008-9-4 20:12:12

//获取日期
DateTime.Now.ToLongDateString().ToString();    // 2008年9月4日
DateTime.Now.ToShortDateString().ToString();    // 2008/9/4
DateTime.Now.ToString("yyyy-MM-dd");        // 2008-09-04
DateTime.Now.Date.ToString();            // 2008-9-4 0:00:00

DateTime.Now.ToString("yyyy-MM-dd HH:mm:ss"); 

//获取时间
DateTime.Now.ToLongTimeString().ToString();   // 20:16:16
DateTime.Now.ToShortTimeString().ToString();   // 20:16
DateTime.Now.TimeOfDay.ToString();        // 20:33:50.7187500
// 24小时制
DateTime.Now.ToString("HH:mm:ss"); // 20:22:33 24小时制
// 毫秒
DateTime.Now.ToString("yyyy-MM-dd HH:mm:ss:fff")

// 单独获取日期、时间 .net 6
DateOnly dateOnly = new(2021, 9, 25);
Console.WriteLine(dateOnly);

TimeOnly timeOnly = new(19, 0, 0);
Console.WriteLine(timeOnly); 

DateOnly dateOnlyFromDate = DateOnly.FromDateTime(DateTime.Now);
Console.WriteLine(dateOnlyFromDate); 

TimeOnly timeOnlyFromDate = TimeOnly.FromDateTime(DateTime.Now);
Console.WriteLine(timeOnlyFromDate); 

//其他
DateTime.ToFileTime().ToString();       // 128650040212500000
DateTime.Now.ToFileTimeUtc().ToString();   // 128650040772968750
DateTime.Now.ToOADate().ToString();       // 39695.8461709606
DateTime.Now.ToUniversalTime().ToString();   // 2008-9-4 12:19:14

DateTime.Now.Year.ToString();         获取年份  // 2008
DateTime.Now.Month.ToString();      获取月份   // 9
DateTime.Now.DayOfWeek.ToString(); 获取星期   // Thursday
DateTime.Now.DayOfYear.ToString(); 获取第几天   // 248
DateTime.Now.Hour.ToString();          获取小时   // 20
DateTime.Now.Minute.ToString();     获取分钟   // 31
DateTime.Now.Second.ToString();     获取秒数   // 45

//n为一个数,可以数整数,也可以事小数
dt.AddYears(n).ToString();   //时间加n年
dt.AddDays(n).ToString();   //加n天
dt.AddHours(n).ToString();   //加n小时
dt.AddMonths(n).ToString();   //加n个月
dt.AddSeconds(n).ToString();   //加n秒
dt.AddMinutes(n).ToString();   //加n分

字符串转时间

var dateTime = DateTime.ParseExact("2020-01-04 16:54", "yyyy-MM-dd HH:mm", null);
var strDate = dateTime.ToString("yyyy-MM-dd HH:mm:ss");

string strFormat = "yyyy-MM-dd HH:mm:ss";
skip_retryFormat:
string strDate = "";
try
{
	var dateTime = DateTime.ParseExact(colsStr[0], strFormat, null);
	strDate = dateTime.ToString("yyyy-MM-dd HH:mm:ss");
}
catch(System.FormatException ex)
{
	if (strFormat != "yyyy/M/d HH:mm:ss")
	{
		strFormat = "yyyy/M/d HH:mm:ss";
		goto skip_retryFormat;
	}else
	{
		MessageBox.Show("数据日期格式不支持，请联系技术支持");
	}
	
}

加减

//昨天，就是今天的日期减一   
DateTime.Now.AddDays(-1).ToShortDateString();   
//明天，同理，加一   
DateTime.Now.AddDays(1).ToShortDateString();

函数执行时间

static void SubTest()
{
	DateTime beforDT = System.DateTime.Now;  
 
	//耗时的代码
	
	DateTime afterDT = System.DateTime.Now;
	TimeSpan ts = afterDT.Subtract(beforDT);
	Console.WriteLine("DateTime总共花费{0}ms.", ts.TotalMilliseconds);
	// {ts.Minutes}分{ts.Seconds}秒
}

static void SubTest()
{
	Stopwatch sw = new Stopwatch();
	sw.Start();
  
	//耗时巨大的代码
	
	sw.Stop();
	TimeSpan ts2 = sw.Elapsed;
	Console.WriteLine("Stopwatch总共花费{0}ms.", ts2.TotalMilliseconds);
}

[System.Runtime.InteropServices.DllImport("Kernel32.dll")]
static extern bool QueryPerformanceCounter(ref long count);
[System.Runtime.InteropServices.DllImport("Kernel32.dll")]
static extern bool QueryPerformanceFrequency(ref long count);   
static void SubTest()
{
	long count = 0;
	long count1 = 0;
	long freq = 0;
	double result = 0;
	QueryPerformanceFrequency(ref freq);
	QueryPerformanceCounter(ref count);   
 
	//耗时巨大的代码
	
	QueryPerformanceCounter(ref count1);
	count = count1 - count;
	result = (double)(count) / (double)freq;
	Console.WriteLine("QueryPerformanceCounter耗时: {0} 秒", result);
}

timer

System.Timers.Timer

不会抛异常精度大约在10ms~20ms之间

//实例化Timer类，设置间隔时间为10000毫秒； 
System.Timers.Timer t =  new System.Timers.Timer(10000);  
  
//到达时间的时候执行事件； 
t.Elapsed +=  new System.Timers.ElapsedEventHandler(theout);  

//设置是执行一次（false）还是一直执行(true)；   
t.AutoReset = true;  

//需要调用 timer.Start()或者timer.Enabled = true来启动它， timer.Start()的内部原理还是设置timer.Enabled = true;
t.Enabled = true;

public void theout(object source, System.Timers.ElapsedEventArgs e)
{
 
}

Threading.Timer

会抛异常精度也只能达到20ms

private System.Threading.Timer timerClose;
timerClose = new System.Threading.Timer(new TimerCallback(timerCall), this, 5000, 0);
 
private void timerCall(object obj)
{
timerClose.Dispose();
this.Close();
}

DispatcherTimer(WPF timer)

需要注意的是在wpf中涉及到界面操作的话，一定要使用 DispatcherTime, DispatcherTimer 是为wpf专门设计的，不然的话会提示界面资源被其他线程所拥有而无法更新界面。

public DispatcherTimerSample()
{
	InitializeComponent();
	DispatcherTimer timer = new DispatcherTimer();
	timer.Interval = TimeSpan.FromSeconds(1);
	timer.Tick += timer_Tick;
	timer.Start();
}

void timer_Tick(object sender, EventArgs e)
{
	lblTime.Content = DateTime.Now.ToLongTimeString();
}

private System.Windows.Threading.DispatcherTimer TimerState = new System.Windows.Threading.DispatcherTimer();
TimerState.Tick += new EventHandler(OnTimerDispatcher);
TimerState.Interval = TimeSpan.FromSeconds(10);
TimerState.Tag = 1;
TimerState.Start();
 
public void OnTimerDispatcher(object sender, EventArgs e)
{
  ((System.Windows.Threading.DispatcherTimer)sender).Stop();
}

// 立即执行，然后在间隔执行
readDataTimer.Tick += new EventHandler(timeCycleRead);
// 15秒 
readDataTimer.Interval = TimeSpan.FromSeconds(0);

public void timeCycleRead(object sender, EventArgs e)
{
	if(readDataTimer.Interval == TimeSpan.FromSeconds(0))
	{
		// 15秒 
		readDataTimer.Interval = TimeSpan.FromSeconds(15);
	}
	//((System.Windows.Threading.DispatcherTimer)sender).Stop();
	if (FLAG_REALTIME != (flag & FLAG_REALTIME))
	{
		btnRealtime_Click(null, null);
		file_index += 1;
	}
	else
	{
		btnStopRealtime_Click(null, null);
	}
}