[英]DateTime.TryParseExact only working in “One Way”
Scope: 范围:
I have been trying to develop a super-tolerant
DateTime.Parse routine, so I decided to give most "widely-used" formats a try to better understand the format masks
. 我一直在尝试开发一个
super-tolerant
DateTime.Parse例程,因此我决定尝试使用大多数“广泛使用”的格式来更好地理解format masks
。
Problem: 问题:
I have defined a specific format (String) which I use as myDate.ToString(format)
, and it works wonders. 我已经定义了一个特定的格式(String),我用它作为
myDate.ToString(format)
,它可以myDate.ToString(format)
奇迹。 The problem is, If I get this same String (result of the .ToString(format)
operation), and feed it back to DateTime.TryParseExact (...)
it fails. 问题是,如果我得到相同的String(
.ToString(format)
操作的结果),并将其反馈给DateTime.TryParseExact (...)
则失败。
Code / Test: 代码/测试:
System.Globalization.CultureInfo provider = System.Globalization.CultureInfo.InvariantCulture;
// Defining Format and Testing it via "DateTime.ToString(format)"
string format = "MM/dd/yyyy HH:mm:ss tt";
string dtNow = DateTime.Now.ToString (format);
Console.WriteLine (dtNow);
// Trying to Parse DateTime on the same Format defined Above
DateTime time;
if (DateTime.TryParseExact (dtNow, format, provider, System.Globalization.DateTimeStyles.None, out time))
{
// If TryParseExact Worked
Console.WriteLine ("Result: " + time.ToString ());
}
else
{
// If TryParseExact Failed
Console.WriteLine ("Failed to Parse Date");
}
Output is : "Failed to Parse Date".
输出为:
"Failed to Parse Date".
Question: 题:
Why can I use the format
string to format a certain date as text, but I can't use the same format
to feed the string back to a date object ? 为什么我可以使用
format
字符串将某个日期格式化为文本,但是我不能使用相同的format
将字符串反馈给日期对象?
EDIT: 编辑:
I have added part of my method to this example , and I would like to know why the "ParseDate" method fails to return a proper date, given that the "String" is in the right format. 我已将此方法的一部分添加到此示例中 ,并且我想知道为什么“ParseDate”方法无法返回正确的日期,因为“String”的格式正确。
Since you use DateTime.ToString()
method without any IFormatProvider
, this method will use your CurrentCulture
settings. 由于您使用
DateTime.ToString()
方法而没有任何IFormatProvider
,因此此方法将使用您的CurrentCulture
设置。
That's why your 这就是你的原因
string dtNow = DateTime.Now.ToString (format);
line might generate a different string representation than MM/dd/yyyy HH:mm:ss tt
format. line 可能会生成与
MM/dd/yyyy HH:mm:ss tt
格式不同的字符串表示形式。
Three things can cause this issue; 有三件事可能导致这个问题;
CurrentCulture
has a different DateSeparator
than /
CurrentCulture
有一个不同的DateSeparator
不是/
CurrentCulture
has a different TimeSeparator
than :
CurrentCulture
具有与以下不同的TimeSeparator
:
CurrentCulture
has a different or empty string as a AMDesignator
and/or PMDesignator
CurrentCulture
有一个不同的或空的字符串作为AMDesignator
和/或PMDesignator
Since you try to parse your string with provider
(which is InvariantCulture
) on your DateTime.TryParseExact
method, generate your string based on that provider as well. 由于您尝试使用
DateTime.TryParseExact
方法的provider
(即InvariantCulture
)解析字符串,因此也要根据该提供程序生成字符串。
string dtNow = DateTime.Now.ToString(format, provider);
You told your CurrentCulture
is pt-BR
and this culture has empty string ""
as a AMDesignator
and PMDesignator
. 你告诉你的
CurrentCulture
是pt-BR
,这种文化有空字符串""
作为AMDesignator
和PMDesignator
。 That's why your dtNow
string will not have any AM or PM designator on it's representation part. 这就是为什么你的
dtNow
字符串在其表示部分没有任何AM或PM指示符的原因。
Here a demonstration
. 这是一个
demonstration
。
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