c# - 带有 TryParseExact 的 FormatException

Question

我想将输入的时间格式化为特定标准:

private String CheckTime(String value)
{
    String[] formats = { "HH mm", "HHmm", "HH:mm", "H mm", "Hmm", "H:mm", "H" };
    DateTime expexteddate;
    if (DateTime.TryParseExact(value, formats, System.Globalization.CultureInfo.InvariantCulture, System.Globalization.DateTimeStyles.None, out expexteddate))
       return expexteddate.ToString("HH:mm");
    else
       throw new Exception(String.Format("Not valid time inserted, enter time like: {0}HHmm", Environment.NewLine));
}

当用户输入时:“09 00”、“0900”、“09:00”、“9 00”、“9:00”
但是当用户输入类似:"900" 或 "9" 时，系统无法格式化它，为什么？它们是我接受的默认格式。

string str = CheckTime("09:00"); // works
str = CheckTime("900");          // FormatException at TryParseExact

Answer 1

Hmm 匹配“0900”，H 匹配“09”，你必须给出 2 个数字。

你可以这样改变用户输入:

private String CheckTime(String value)
{
    // change user input into valid format
    if(System.Text.RegularExpressions.Regex.IsMatch(value, "(^\\d$)|(^\\d{3}$)"))
        value = "0"+value;

    String[] formats = { "HH mm", "HHmm", "HH:mm", "H mm", "Hmm", "H:mm", "H" };
    DateTime expexteddate;
    if (DateTime.TryParseExact(value, formats, System.Globalization.CultureInfo.InvariantCulture,     System.Globalization.DateTimeStyles.None, out expexteddate))
       return expexteddate.ToString("HH:mm");
    else
       throw new Exception(String.Format("Not valid time inserted, enter time like:     {0}HHmm", Environment.NewLine));
}