FormatException与TryParseExact

Question

我想将输入的时间格式化为特定的标准：

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));
}

当用户键入"09 00“、"0900”、"09:00“、"9 00”、"9:00“时

但是当用户输入它时："900"或"9"，系统无法格式化它，为什么？它们是默认格式。

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

Answer 1

嗯，匹配"0900“和H匹配"09”，你必须给出2位数字。

您可以这样更改用户输入：

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));
}

Answer 2

字符串时间= "900".PadLeft(4，'0')；

如果值为0900,900,9，甚至0，请注意上面的行;)