使用DateTime的ParseExact方法实现特殊日期时间的方法详解（转）-阿里云开发者社区

本篇文章是对使用DateTime的ParseExact方法实现特殊日期时间的方法进行了详细的分析介绍，需要的朋友参考下
今天遇到一个特别的需求，需要从下面的字符串中转换成一个DateTime对象：

[07-13 15:50:42]

主要问题是这个时间不是标准的时间，而是自定义的格式，即开头是月-日，然后是时间。
使用最常用的DateTime.Parse(string dateTimeStr)无法转换，问题就在于这个自定义格式上。
搜索了之后，我找到了下面的方法：

public static DateTime ParseExact(
 string s,
 string format,
 IFormatProvider provider
)

使用例子如下：

var dateTimeStr = "07-13 15:50:42";
var dateTime = DateTime.ParseExact(dateTimeStr, "MM-dd HH:mm:ss", CultureInfo.InvariantCulture);

使用效果如下:

如果你使用的其它特殊语言，比如美国或者日文啥的，最后的参数你可能需要获取下对应的Culture。
注意：
•如果dateTimeStr或者format 是null，会抛出ArgumentNullException异常。
•如果dateTimeStr或者format 是空字符串，则抛出FormatException异常。

DateTime.ParseExact Method (String, String, IFormatProvider)

Converts the specified string representation of a date and time to its DateTime equivalent using the specified format and culture-specific format information. The format of the string representation must match the specified format exactly.

public static DateTime ParseExact(
    string s,
    string format,
    IFormatProvider provider
)

Parameters
s
Type: System.String
A string that contains a date and time to convert.
format
Type: System.String
A format specifier that defines the required format of s. For more information, see the Remarks section.
provider
Type: System.IFormatProvider
An object that supplies culture-specific format information about s.
Return Value
Type: System.DateTime
An object that is equivalent to the date and time contained in s, as specified by format and provider.

Exception
Condition

ArgumentNullException

s or format is null.

FormatException

s or format is an empty string.

-or-

s does not contain a date and time that corresponds to the pattern specified in format.

-or-

The hour component and the AM/PM designator in s do not agree.

The DateTime.ParseExact(String, String, IFormatProvider) method parses the string representation of a date, which must be in the format defined by the formatparameter. It also requires that the <Date> and <Time> elements of the string representation of a date and time appear in the order specified by format, and that shave no white space other than that permitted by format. If format defines a date with no time element and the parse operation succeeds, the resulting DateTimevalue has a time of midnight (00:00:00). If format defines a time with no date element and the parse operation succeeds, the resulting DateTime value has a date ofDateTime.Now.Date.

If s does not represent a time in a particular time zone and the parse operation succeeds, the Kind property of the returned DateTime value isDateTimeKind.Unspecified. If s does represent the time in a particular time zone and format allows time zone information to be present (for example, if format is equal to the "o", "r", or "u" standard format specifiers, or if it contains the "z", "zz", or "zzz" custom format specifiers), the Kind property of the returned DateTimevalue is DateTimeKind.Local.

The format parameter is a string that contains either a single standard format specifier, or one or more custom format specifiers that define the required format of s. For details about valid formatting codes, see Standard Date and Time Format Strings or Custom Date and Time Format Strings.

Note Note

If format is a custom format pattern that does not include date or time separators (such as "yyyyMMdd HHmm"), use the invariant culture for the providerparameter and the widest form of each custom format specifier. For example, if you want to specify hours in the format pattern, specify the wider form, "HH", instead of the narrower form, "H".

The particular date and time symbols and strings (such as names of the days of the week in a particular language) used in s are defined by the provider parameter, as is the precise format of s if format is a standard format specifier string. The provider parameter can be any of the following:

A CultureInfo object that represents the culture used to interpret s. The DateTimeFormatInfo object returned by its DateTimeFormat property defines the symbols and formatting in s.
A DateTimeFormatInfo object that defines the format of date and time data.
A custom IFormatProvider implementation whose GetFormat method returns either the CultureInfo object or the DateTimeFormatInfo object that provides formatting information.

If provider is null, the CultureInfo object that corresponds to the current culture is used.

Notes to Callers

In the .NET Framework 4, the ParseExact method throws a FormatException if the string to be parsed contains an hour component and an AM/PM designator that are not in agreement. In the .NET Framework 3.5 and earlier versions, the AM/PM designator is ignored.

using System;
using System.Globalization;

public class Example
{
   public static void Main()
   {
      string dateString, format;  
      DateTime result;
      CultureInfo provider = CultureInfo.InvariantCulture;

      // Parse date-only value with invariant culture.
      dateString = "06/15/2008";
      format = "d";
      try {
         result = DateTime.ParseExact(dateString, format, provider);
         Console.WriteLine("{0} converts to {1}.", dateString, result.ToString());
      }
      catch (FormatException) {
         Console.WriteLine("{0} is not in the correct format.", dateString);
      } 

      // Parse date-only value without leading zero in month using "d" format.
      // Should throw a FormatException because standard short date pattern of  
      // invariant culture requires two-digit month.
      dateString = "6/15/2008";
      try {
         result = DateTime.ParseExact(dateString, format, provider);
         Console.WriteLine("{0} converts to {1}.", dateString, result.ToString());
      }
      catch (FormatException) {
         Console.WriteLine("{0} is not in the correct format.", dateString);
      }

      // Parse date and time with custom specifier.
      dateString = "Sun 15 Jun 2008 8:30 AM -06:00";
      format = "ddd dd MMM yyyy h:mm tt zzz";
      try {
         result = DateTime.ParseExact(dateString, format, provider);
         Console.WriteLine("{0} converts to {1}.", dateString, result.ToString());
      }
      catch (FormatException) {
         Console.WriteLine("{0} is not in the correct format.", dateString);
      }

      // Parse date and time with offset but without offset's minutes. 
      // Should throw a FormatException because "zzz" specifier requires leading  
      // zero in hours.
      dateString = "Sun 15 Jun 2008 8:30 AM -06";
      try {
         result = DateTime.ParseExact(dateString, format, provider);
         Console.WriteLine("{0} converts to {1}.", dateString, result.ToString());
      }   
      catch (FormatException) {
         Console.WriteLine("{0} is not in the correct format.", dateString);
      } 

      dateString = "15/06/2008 08:30";
      format = "g";
      provider = new CultureInfo("fr-FR");
      try {
         result = DateTime.ParseExact(dateString, format, provider);
         Console.WriteLine("{0} converts to {1}.", dateString, result.ToString());
      }   
      catch (FormatException) {
         Console.WriteLine("{0} is not in the correct format.", dateString);
      } 
   }
}
// The example displays the following output: 
//       06/15/2008 converts to 6/15/2008 12:00:00 AM. 
//       6/15/2008 is not in the correct format. 
//       Sun 15 Jun 2008 8:30 AM -06:00 converts to 6/15/2008 7:30:00 AM. 
//       Sun 15 Jun 2008 8:30 AM -06 is not in the correct format. 
//       15/06/2008 08:30 converts to 6/15/2008 8:30:00 AM.

使用DateTime的ParseExact方法实现特殊日期时间的方法详解（转）

DateTime.ParseExact Method (String, String, IFormatProvider)

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