C＃可为空 <DateTime> 串

Question

I have a DateTime? variable, sometimes the value is null , how can I return an empty string "" when the value is null or the DateTime value when not null ?

Answer 1

Though many of these answers are correct, all of them are needlessly complex. The result of calling ToString on a nullable DateTime is already an empty string if the value is logically null. Just call ToString on your value; it will do exactly what you want.

Answer 2

string date = myVariable.HasValue ? myVariable.Value.ToString() : string.Empty;

Answer 3

Actually, this is the default behaviour for Nullable types, that without a value they return nothing:

public class Test {
    public static void Main() {
        System.DateTime? dt = null;
        System.Console.WriteLine("<{0}>", dt.ToString());
        dt = System.DateTime.Now;
        System.Console.WriteLine("<{0}>", dt.ToString());
    }
}

this yields

<>
<2009-09-18 19:16:09>

Answer 4

在null的Nullable<T>上调用.ToString()将返回一个空字符串。

Answer 5

You could write an extension method

public static string ToStringSafe(this DateTime? t) {
  return t.HasValue ? t.Value.ToString() : String.Empty;
}

...
var str = myVariable.ToStringSafe();

Answer 6

All you need to do is to just simply call .ToString() . It handles Nullable<T> object for null value.

Here is the source of .NET Framework for Nullable<T>.ToString() :

public override string ToString() {
    return hasValue ? value.ToString() : "";
}

Answer 7

DateTime? d;
// stuff manipulating d;
return d != null ? d.Value.ToString() : String.Empty;

Answer 8

DateTime? MyNullableDT;
....
if (MyNullableDT.HasValue)
{
    return MyNullableDT.Value.ToString();
}
return "";

Answer 9

if (aDate.HasValue)
    return aDate;
else
    return string.Empty;

Answer 10

DateTime d?;
string s = d.HasValue ? d.ToString() : string.Empty;

Answer 11

According to Microsoft's documentation :

The text representation of the value of the current Nullable object if the HasValue property is true, or an empty string ("") if the HasValue property is false.