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.