Writing my own IsDate function in VB - vb.net

Question

I have had problems with VB.NET IsDate function - it returns true on string values that are not a valid date, such as "367 7" and "10,600" etc. So I have decided to write my own function and wanted to hear some feedback on possible improvements. Would really appreciate valuable input.
Function IsValidDate(ByVal str As String) As Boolean
str = str.Replace(" ", "").Trim()
'If (str Is Nothing) Then
' Return False
'End If
'If IsNumeric(str) Then
' Return False
'End If
'If Regex.IsMatch(str, "^[A-Za-z ]+$") Then
' Return False
'End If
If Regex.IsMatch(str, "^(0[1-9]|1[012])[- /.](0[1-9]|[12][0-9]|3[01])[- /.](19|20)\d\d$") Then
''mm/dd/yyyy or mm-dd-yyyy
Return True
ElseIf Regex.IsMatch(str, "^(0[1-9]|1[012])[- /.](0[1-9]|[12][0-9]|3[01])[- /.]\d\d$") Then
''mm/dd/yy or mm-dd-yy
Return True
ElseIf Regex.IsMatch(str, "^(0[1-9]|[12][0-9]|3[01])[- /.](0[1-9]|1[012])[- /.](19|20)\d\d$") Then
''dd-mm-yyyy or dd/mm/yyyy
Return True
ElseIf Regex.IsMatch(str, "^(19|20)\d\d[- /.](0[1-9]|1[012])[- /.](0[1-9]|[12][0-9]|3[01])$") Then
''yyyy-mm-dd or yyyy/mm/dd
Return True
End If
Return False
End Function
I took care of a possible space in the numeric string (ex.: "367 7", then I made sure it returns false if the value is numeric or nothing. I also eliminated strings that are all alphanumeric. Please let me know what do you think. Thank you
P.S> Edit: I commented out a few lines in the beginning as I felt they could be eliminated since if the string does not match one of the regexes, it will return false anyway

Answer 1

Have tried something like this?
Function IsValidDate(ByVal str As String) As Boolean
Dim test As Date
If Date.TryParseExact(str, "yyyy/MM/dd HH:mm:ss", System.Globalization.CultureInfo.CurrentCulture, Globalization.DateTimeStyles.None, test) Then
Return True
Else
Return False
End If
End Function
From here you can just change the format in the quotes.
!EDIT!
I can't add comments because of my reputation, but if have your array of formats like in your comment and use my code, instead of the format I have in there, put your array formats in its' place. It worked fine for me.
Dim test As Date
Dim formats As String() = {"MM/dd/yyyy", "MM-dd-yyyy", "MM/dd/yy", "MM-dd-yy", "M-d-yyyy", "M/d/yyyy", "M/d/yyyy h:mm:ss tt", "M/d/yyyy h:mm tt", "MM/dd/yyyy hh:mm:ss", "M/d/yyyy h:mm:ss", "M/d/yyyy hh:mm tt", "M/d/yyyy hh tt", _
"M/d/yyyy h:mm", "M/d/yyyy h:mm", "MM/dd/yyyy hh:mm", "M/dd/yyyy hh:mm"}
If Date.TryParseExact(str, formats, System.Globalization.CultureInfo.CurrentCulture, Globalization.DateTimeStyles.None, test) Then
Return True
Else
Return False
End If
This won't reorganize your input, but rather just a Boolean return to see if it matches the format you specify, which is what you originally wanted correct?

Answer 2

Running into this situation in my own code, I found that the 'TryParseExact' function is significantly slower than using a series of 'Regex.Match' calls.
This is the function that I wrote to check the formats I am looking for and it ran about 10x faster than TryParseExact.
The downside of this over TryParseExact is that it does not check all of the edge cases, such as '31 is not a valid day in November' or '29 is not a valid day in Feb on certain years'. So as long as you are willing to give up those catches, then this is faster.
Public Shared Function ChkDate(ByVal Value As Object) As Boolean
If Value.GetType().Name = "DateTime" Then
Return True
ElseIf Not String.IsNullOrWhiteSpace(Value.ToString()) Then
Dim TempStr As String = Value.ToString()
' Please speed test before making any changes to this function, the below version is much faster than Date.TryParse or Date.TryParseExact
If InStr(TempStr, ".") <> 0 AndAlso TempStr.Split({"."c}).Length = 3 Then ' d.M.yyyy
Dim TempArray() As String = TempStr.Split({"."c})
Dim NewString As String = TempArray(1) & "/" & TempArray(0) & "/" & TempArray(2)
ElseIf InStr(TempStr, "/") <> 0 AndAlso RegularExpressions.Regex.IsMatch(TempStr, "\A[01]{0,1}[0-9]{1}/[0123]{0,1}[0-9]{1}/[0-9]{4}\z") Then ' M/d/yyyy
Return True
ElseIf InStr(TempStr, "-") <> 0 AndAlso RegularExpressions.Regex.IsMatch(TempStr, "\A[0-9]{4}-[01]{0,1}[0-9]{1}-[0123]{0,1}[0-9]{1}\z") Then ' yyyy-M-d
Return True
ElseIf InStr(TempStr, "-") <> 0 AndAlso InStr(TempStr, ":") <> 0 AndAlso RegularExpressions.Regex.IsMatch(TempStr, "\A[0-9]{4}-[01]{0,1}[0-9]{1}-[0123]{0,1}[0-9]{1} [01]{0,1}[0-9]{1}:[01]{0,1}[0-6]{1}:[01]{0,1}[0-6]{1}\z") Then ' yyyy-M-d H:mm:ss
Return True
ElseIf InStr(TempStr, "/") <> 0 AndAlso InStr(TempStr, ":") <> 0 AndAlso RegularExpressions.Regex.IsMatch(TempStr, "\A[01]{0,1}[0-9]{1}/[0123]{0,1}[0-9]{1}/[0-9]{4} [01]{0,1}[0-9]{1}:[01]{0,1}[0-6]{1}\z") Then ' M/d/yyyy h:mm
Return True
ElseIf RegularExpressions.Regex.IsMatch(TempStr, "\A[0-9]{4}[01]{1}[0-9]{1}[0123]{1}[0-9]{1}\z") Then ' yyyyMMdd
Return True
ElseIf RegularExpressions.Regex.IsMatch(TempStr, "\A[0-9]{4}[01]{0,1}[0-9]{1}[0123]{0,1}[0-9]{1}[01]{0,1}[0-9]{1}[01]{0,1}[0-6]{1}\z") Then ' yyyyMMddHHmm
Return True
Else
Return IsDate(TempStr)
End If
End If
Return False
End Function

Answer 3

Rather than using the Regexes, have you looked at DateTime.ParseExact? It lets you define the exact formats you support.