Cannot implicitly convert type 'System.DateTime?' to 'System.DateTime'. An explicit conversion exists

Question

I am trying to convert DateTime? to DateTime but I get this Error:

Error 7 Cannot implicitly convert type 'System.DateTime?' to 'System.DateTime'. An explicit conversion exists

Here is my code:

public string ConvertToPersianToShow(DateTime?  datetime)
{
  DateTime dt;
  string date;
  dt = datetime;
    
  string year = Convert.ToString(persian_date.GetYear(dt));
  string month = Convert.ToString(persian_date.GetMonth(dt));
  string day = Convert.ToString(persian_date.GetDayOfMonth(dt));
    
  if (month.Length == 1)
  {
     month = "0" + Convert.ToString(persian_date.GetMonth(dt));
  }
  if (day.Length == 1)
  {
     day = "0" + Convert.ToString(persian_date.GetDayOfMonth(dt));
  }

  //date = Convert.ToString(persian_date.GetYear(dt)) + "/" + 
  Convert.ToString(persian_date.GetMonth(dt)) + "/" +
  //Convert.ToString(persian_date.GetDayOfMonth(dt));
  date = year + "/" + month + "/" + day+"("+dt.Hour+":"+dt.Minute+")";

  return date;
}

Solution 1

You have 3 options:

1) Get default value

dt = datetime??DateTime.Now;

it will assign DateTime.Now (or any other value which you want) if datetime is null

2) Check if datetime contains value and if not return empty string

if(!datetime.HasValue) return "";
dt = datetime.Value;

3) Change signature of method to

public string ConvertToPersianToShow(DateTime  datetime)

It's all because DateTime? means it's nullable DateTime so before assigning it to DateTime you need to check if it contains value and only then assign.

Solution 2

dt is nullable you need to access its Value

if (datetime.HasValue)
    dt = datetime.Value;

It is important to remember that it can be NULL. That is why the nullablestruct has the HasValue property that tells you if it is NULL or not.

You can also use the null-coalescing operator ?? to assign a default value

dt = datetime ?? DateTime.Now;

This will assign the value on the right if the value on the left is NULL

Solution 3

The problem is that you are passing a nullable type to a non-nullable type.

You can do any of the following solution:

A. Declare your dt as nullable

DateTime? dt = dateTime;

B. Use Value property of the the DateTime? datetime

DateTime dt = datetime.Value;

C. Cast it

DateTime dt = (DateTime) datetime;

Solution 4

you should be using the .Value of the datetime parameter. All Nullable structs have a value property which returns the concrete type of the object. but you must check to see if it is null beforehand otherwise you will get a runtime error.

i.e:

datetime.Value

but check to see if it has a value first!

if (datetime.HasValue)
{
   // work with datetime.Value
}

View more solutions

Comments

[Piotr Justyna]

This is your problem: dt = datetime; You should check if the datetime has value (HasValue) and then try to get it, or act accordingly if the value is not there.

[Admin]

I changed it some thing like that :DateTime dt=DateTime.Now;

[Kamil Budziewski]

@EhsanAkbar maybe change it to DateTime dt = datetime??DateTime.Now?

[David Pilkington]

Yes, as I mentioned in my answer. That way you get to keep your value if there is one

[Millie Smith]

I don't think ?? works here. Datetime on the left still can't be converted. I think you have to do datetime.HasValue ? datetime.Value : DateTime.Now

[Kamil Budziewski]

@MillieSmith nope, ?? means it, exactly datetime.HasValue ? datetime.Value : DateTime.Now it's just short version of that

[Millie Smith]

I know that. I just don't remember the compiler figuring that out (even though it should be able to).

[Cromwell]

?? works like a charm but we are using current date as the default. what is i want to assign, for example, 1.1.2000 as default date?

[Kamil Budziewski]

@Cromwell use dt = datetime??new DateTime(2000,1,1);