How to validate GUID is a GUID

How to determine if a string contains a GUID vs just a string of numbers.

will a GUID always contain at least 1 alpha character?

See if these helps :-

1. Guid.Parse - Docs

Guid guidResult = Guid.Parse(inputString)

2. Guid.TryParse - Docs

bool isValid = Guid.TryParse(inputString, out guidOutput)

When I'm just testing a string to see if it is a GUID, I don't really want to create a Guid object that I don't need. So...

public static class GuidEx
{
    public static bool IsGuid(string value)
    {
        Guid x;
        return Guid.TryParse(value, out x);
    }
}

And here's how you use it:

string testMe = "not a guid";
if (GuidEx.IsGuid(testMe))
{
...
}

A GUID is a 16-byte (128-bit) number, typically represented by a 32-character hexadecimal string. A GUID (in hex form) need not contain any alpha characters, though by chance it probably would. If you are targeting a GUID in hex form, you can check that the string is 32-characters long (after stripping dashes and curly brackets) and has only letters A-F and numbers.

There is certain style of presenting GUIDs (dash-placement) and regular expressions can be used to check for this, e.g.,

@"^(\{{0,1}([0-9a-fA-F]){8}-([0-9a-fA-F]){4}-([0-9a-fA-F]){4}-([0-9a-fA-F]){4}-([0-9a-fA-F]){12}\}{0,1})$"

from http://www.geekzilla.co.uk/view8AD536EF-BC0D-427F-9F15-3A1BC663848E.htm. That said, it should be emphasized that the GUID really is a 128-bit number and could be represented in a number of different ways.

There is no guarantee that a GUID contains alpha characters. FFFFFFFF-FFFF-FFFF-FFFF-FFFFFFFFFFFF is a valid GUID so is 00000000-0000-0000-0000-000000000000 and anything in between.

If you are using .NET 4.0, you can use the answer above for the Guid.Parse and Guid.TryParse. Otherwise, you can do something like this:

public static bool TryParseGuid(string guidString, out Guid guid)
{
    if (guidString == null) throw new ArgumentNullException("guidString");
    try
    {
        guid = new Guid(guidString);
        return true;
    }
    catch (FormatException)
    {
        guid = default(Guid);
        return false;
    }
}

This is a fairly clean, modern C# approach that suppresses the out variable:

var isValid = Guid.TryParse(inputString, out _);

Based on the accepted answer I created an Extension method as follows:

public static Guid ToGuid(this string aString)
{
    Guid newGuid;

    if (string.IsNullOrWhiteSpace(aString))
    {
        return MagicNumbers.defaultGuid;
    }

    if (Guid.TryParse(aString, out newGuid))
    {
        return newGuid;
    }

    return MagicNumbers.defaultGuid;
}

Where "MagicNumbers.defaultGuid" is just "an empty" all zero Guid "00000000-0000-0000-0000-000000000000".

In my case returning that value as the result of an invalid ToGuid conversion was not a problem.

if(MyGuid != Guid.Empty) 
{
   // Valid Guid
} 
else
{
   // Invalid Guid
}

see http://en.wikipedia.org/wiki/Globally_unique_identifier

There is no guarantee that an alpha will actually be there.

Will return the Guid if it is valid Guid, else it will return Guid.Empty

if (!Guid.TryParse(yourGuidString, out yourGuid)){
          yourGuid= Guid.Empty;
}

Use GUID constructor standard functionality

Public Function IsValid(pString As String) As Boolean

    Try
        Dim mGuid As New Guid(pString)
    Catch ex As Exception
        Return False
    End Try
    Return True

End Function