问如何确定路径是否完全合格？

EN

Public Class PathEx
    Public Shared Function IsPathFullyQualified(path As String) As Boolean
        If path Is Nothing Then
            Throw New ArgumentNullException(NameOf(path))
        End If

        Return Not IsPartiallyQualified(path)
    End Function

    Private Shared Function IsPartiallyQualified(path As String) As Boolean
        If path.Length < 2 Then
            ' It isn't fixed, it must be relative.  There is no way to specify a fixed
            ' path with one character (or less).
            Return True
        End If

        If IsDirectorySeparator(path.Chars(0)) Then
            ' There is no valid way to specify a relative path with two initial slashes or
            ' \? as ? isn't valid for drive relative paths and \??\ is equivalent to \\?\
            Return Not (path.Chars(1) = "?"c OrElse IsDirectorySeparator(path.Chars(1)))
        End If

        ' The only way to specify a fixed path that doesn't begin with two slashes
        ' is the drive, colon, slash format- i.e. C:\
        Return Not ((path.Length >= 3) AndAlso
                    (path.Chars(1) = IO.Path.VolumeSeparatorChar) AndAlso
                    IsDirectorySeparator(path.Chars(2)) AndAlso
                    IsValidDriveChar(path.Chars(0)))
        '           ^^^^^^^^^^^^^^^^
        ' To match old behavior we'll check the drive character for validity as
        ' the path is technically not qualified if you don't have a valid drive.
        ' "=:\" is the "=" file's default data stream.
    End Function

    Private Shared Function IsDirectorySeparator(c As Char) As Boolean
        Return c = Path.DirectorySeparatorChar OrElse c = Path.AltDirectorySeparatorChar
    End Function

    Private Shared Function IsValidDriveChar(value As Char) As Boolean
        Return (value >= "A"c AndAlso value <= "Z"c) OrElse
               (value >= "a"c AndAlso value <= "z"c)
    End Function
End Class

Console.WriteLine(PathEx.IsPathFullyQualified("C:Documents"))    ' False
Console.WriteLine(PathEx.IsPathFullyQualified("/Documents"))     ' False
Console.WriteLine(PathEx.IsPathFullyQualified("C:\Documents"))   ' True

public static bool IsPathFullyQualified(string path)
{
    if (path == null)
        throw new ArgumentNullException(nameof(path));
    return path.Length >= 3 && path[1] == System.IO.Path.VolumeSeparatorChar && ( path[2] == System.IO.Path.DirectorySeparatorChar | path[2] == System.IO.Path.AltDirectorySeparatorChar );
}

public static bool IsPathFullyQualified(string path)
        {
            if (path == null) throw new ArgumentNullException(nameof(path));
            if (path.Length < 2) return false; //There is no way to specify a fixed path with one character (or less).
            if (path.Length == 2 && IsValidDriveChar(path[0]) && path[1] == System.IO.Path.VolumeSeparatorChar) return true; //Drive Root C:
            if (path.Length >= 3 && IsValidDriveChar(path[0]) &&  path[1] == System.IO.Path.VolumeSeparatorChar && IsDirectorySeperator(path[2])) return true; //Check for standard paths. C:\
            if (path.Length >= 3 && IsDirectorySeperator(path[0]) && IsDirectorySeperator(path[1])) return true; //This is start of a UNC path
            return false; //Default
        }

        private static bool IsDirectorySeperator(char c) => c == System.IO.Path.DirectorySeparatorChar | c == System.IO.Path.AltDirectorySeparatorChar;
        private static bool IsValidDriveChar(char c) => c >= 'A' && c <= 'Z' || c >= 'a' && c <= 'z';