如何在C＃中将日期格式用作常量？

Question

I'm using "yyyy-MM-dd" several time in the code for date formatting

For example :

var targetdate = Date.ToString("yyyy-MM-dd");

Is it possible to declare the format as constant, so that use of the code again and again can be avoided

Answer 1

Use an extension method without declare any format again and again like this:

public static class DateExtension
{
    public static string ToStandardString(this DateTime value)
    {
        return value.ToString(
            "yyyy-MM-dd", 
            System.Globalization.CultureInfo.InvariantCulture);
    }
}

So you use it in this way

var targetdate = Date.ToStandardString();

Answer 2

Use this as

const string dateFormat = "yyyy-MM-dd";

//Use 
var targetdate = Date.ToString(dateFormat);

OR

//for public scope
public static readonly string DateFormat = "yyyy-MM-dd";

//Use
var targetdate = Date.ToString(DateFormat);
//from outside the class, you have to use in this way
var targetdate = Date.ToString(ClassName.DateFormat);

Answer 3

Another option that you can do is use the DateTimeFormatInfo overload on .ToString(...) rather than the string overload.

public static readonly System.Globalization.DateTimeFormatInfo MyDateTimeFormatInfo
    = new System.Globalization.DateTimeFormatInfo()
{
    ShortDatePattern = "yyyy-MM-dd",
    LongTimePattern = "",
};

Now you can do var targetdate = DateTime.Now.ToString(MyDateTimeFormatInfo); which is much the same as using string, but you have a lot more control over many other formatting properties.