How do you implement a IEqualityComparer<T> in VB.NET? - vb.net

Question

I have the following function that loops through a directory and checks for a specified folder and file:
Private Function VerifyPath(ByVal root As String, ByVal folder As String, _
ByVal file As String) As Boolean
Dim folders As New List(Of String), files As New List(Of String)
Dim oDir As New IO.DirectoryInfo(root)
For Each dir As IO.DirectoryInfo In oDir.GetDirectories
folders.Add(dir.Name.ToLower)
Next
If folders.Contains(folder) Then
For Each item As IO.FileInfo In oDir.GetFiles
files.Add(item.Name.ToLower)
Next
If files.Contains(file) Then
Return True
End If
End If
Return False
End Function
The reason I did this method is so I could make sure that the items in each list and the passed file/folder were all lower case, otherwise I would have done something like this:
If oDir.GetDirectories.Contains( _
New IO.DirectoryInfo(String.Format("{0}\{1}", root, folder))) Then
If oDir.GetFiles.Contains( _
New IO.FileInfo(String.Format("{0}\{1}", root, file))) Then
Return True
End If
End If
Return False
My colleague mentioned something to me earlier about being able to ignore case by using a comparer. The .Contains extension can have a comparer argument along with the value. I did some searching on google and MSDN, and came up with the following comparer:
Public Class dirCompare
Implements IEqualityComparer(Of IO.DirectoryInfo)
Dim theCompare As CaseInsensitiveComparer
Sub New()
theCompare = CaseInsensitiveComparer.DefaultInvariant
End Sub
Sub New(ByVal culture As CultureInfo)
theCompare = New CaseInsensitiveComparer(culture)
End Sub
Public Function Equals1(ByVal x As System.IO.DirectoryInfo, ByVal y As System.IO.DirectoryInfo) As Boolean Implements System.Collections.Generic.IEqualityComparer(Of System.IO.DirectoryInfo).Equals
If theCompare.Compare(x.name, y.name) = 0 Then
Return True
Else
Return False
End If
End Function
Public Function GetHashCode1(ByVal obj As System.IO.DirectoryInfo) As Integer Implements System.Collections.Generic.IEqualityComparer(Of System.IO.DirectoryInfo).GetHashCode
Return obj.ToString.ToLower.GetHashCode
End Function
End Class
When it gets to the theCompare(x.name, y.name) = 0 line, it errors out and this is the error message:
At least one object must implement IComparable.
Anyone know what this error means and how to go about correcting it?

Answer 1

Well you could implement a comparer, but that would be the hard way in this case. You have a couple other options available instead.
The first is that there is already a case-insensitive comparer you can use. There are a couple actually. Look in your intellisense prompts under System.StringComparer.
The second is that strings already have a built-in way to specify a case-insensitive compare:
Dim s As String = "a"
Dim t As String = "A"
If s.Equals(t, StringComparison.InvariantCultureIgnoreCase) Then
''//...
End If
And a third is that any searchPattern passed to Directory.GetFiles() or Directory.GetDirectories() is passed directly to the operating system, and Windows is only case-aware for file names, not case-sensitive. So you can pass your folder and file as a search pattern and do your lookup that way.