c# - 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;
}

Answer 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.