[英]DateTime.Now and NullReferenceException
In my business object I have to obtain the current hour (a DateTime with minutes and seconds = 0). 在我的业务对象中,我必须获取当前小时(具有分钟和秒= 0的DateTime)。
I have created a function like this: 我创建了这样的函数:
private DateTime GetCurrentHour()
{
return DateTime.Today.AddHours(DateTime.Now.Hour);
}
If I use it in this way 如果我用这种方式
var lastHour=GetCurrentHour();
I get a NullReferenceException ???? 我得到了NullReferenceException ????
Using in the same function in this way: 以这种方式使用相同的功能:
var ora = new NHRepository<OraProduzione>(Session)
.First(x => x.Data == GetCurrentHour().AddHours(-1));
I get no exception Why? 我也不例外,为什么?
This is the stacktrace: 这是堆栈跟踪:
in ImpelSystems.Produzione.Business.Calendario.TimerWakeUp() in \Calendario.cs:riga 115
in ImpelSystems.Produzione.Business.Calendario.<.ctor>b__1(Object x) in \Calendario.cs:riga 78
in System.Threading._TimerCallback.TimerCallback_Context(Object state)
in System.Threading.ExecutionContext.runTryCode(Object userData)
in System.Runtime.CompilerServices.RuntimeHelpers.ExecuteCodeWithGuaranteedCleanup(TryCode code, CleanupCode backoutCode, Object userData)
in System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state)
in System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
in System.Threading._TimerCallback.PerformTimerCallback(Object state)
TimerWakeUp is executed on a Timer created with TimerWakeUp在使用以下命令创建的计时器上执行
timer = new System.Threading.Timer(x => TimerWakeUp(), null, new TimeSpan(0, 0, 0, 10), new TimeSpan(0, 0, 0, 10));
Are you certain that your exception is on var lastHour=GetCurrentHour();
您确定您的异常在
var lastHour=GetCurrentHour();
上var lastHour=GetCurrentHour();
? ? The
DateTime
type is a struct, which should make it (unless I'm missing something) impossible for you to encounter a null reference. DateTime
类型是一个结构,应该使它(除非我缺少某些东西)使您不可能遇到空引用。
Additionally, I'm assuming you meant DateTime.Today.AddHours(DateTime.Now.Hour)
, as the Today
property is static, so you couldn't access it from the instance returned from Now
. 另外,我假设您的意思是
DateTime.Today.AddHours(DateTime.Now.Hour)
,因为Today
属性是静态的,所以您无法从Now
返回的实例中访问它。
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