区分对象是 DateTime 类型还是 Nullable<DateTime> (DateTime?)

Question

如何区分对象是 DateTime 类型还是 NullableDateTime>（DateTime？）类型？

我明白为什么下面的代码不起作用，但你能帮我提供一个可行的解决方案吗？

    public void Test()
    {
        DateTime? dateTime1 = new DateTime(2020, 1, 1);
        DateTime dateTime2 = new DateTime(2020, 1, 1);
        DoSomething(dateTime1);
        DoSomething(dateTime2);
    }

    public void DoSomething(object value)
    {
        if (value is DateTime?)
        {
            //Do something
        }
        if (value is DateTime)
        {
            //Do something else
        }
    }

Answer 1

这是不可能的，因为 C# 中的可空值类型 boxed：

If HasValue returns false, the null reference is produced.

If HasValue returns true, the corresponding value of the underlying value type T is boxed, not the instance of Nullable.

所以基本上没有装箱的可空值类型这样的东西。

不确定您的实际情况，但在提供的情况下，您可以使您的方法通用并使用 Nullable.GetUnderlyingType:

public void DoSomething<T>(T value)
{
    var typeOfT = typeof(T);
    if(Nullable.GetUnderlyingType(typeOfT) == typeof(DateTime))
    {
        Console.WriteLine("nullable dt");
    }
    else if(typeOfT ==  typeof(DateTime))
    {
        Console.WriteLine("dt");
    }
}

DoSomething(dateTime1); // prints "nullable dt"
DoSomething(dateTime1); // prints "dt"

Answer 2

      public void Test()
      (
        DateTime? dateTime1 = new DateTime(2020, 1, 1); 
        DateTime dateTime2 = new DateTime(2020, 1, 1);
        DateTime? dateTime3 = DateTime.Now;
        DateTime dateTime4 = DateTime.Now.Date;

        **//here you can pass any datetime variable from above**
        DoSomething(dateTime1 == null ? null : dateTime1);
        DoSomething(dateTime2);
       }

   
   public void DoSomething(DateTime? value)
    {
        if (DateTime.TryParse(value.ToString(), out DateTime Temp) == true  && value != null)
        {
            //do stuff if dateTime variable not null & correct formate
            var d = value;
        }
        else
        {
            //do stuff if dateTime variable null
        }
    }

区分对象是 DateTime 类型还是 Nullable<DateTime> (DateTime?)

Differentiate if an object is of type DateTime or Nullable<DateTime> (DateTime?)

c#

datetime

compare

nullable