ansaurus

Question

Sorting an array of folder names like Windows Explorer (Numerically and Alphabetically) - VB.NET

Answer 1

A:

Array.Sort has an IComparer parameter too, you can override sorting behavior if you don't like the default. see Array.Sort Method (T[], IComparer) how to do it

ArsenMkrt 2010-06-23 07:13:32

Answer 2

+4 A:

You would need to implement an IComparer, as opposed to creating a class that implements IComparable. The difference is that an IComparer has the necessary "knowledge" to compare two objects whereas IComparable is implemented by a class that knows how to compare itself against something else.

And the way Windows Explorer sorts filenames is using a function called StrCmpLogicalW. You can use this function in your own IComparer to get the same sort behavior as Windows Explorer. This function treats numeric parts of strings as numbers so that 1 sorts before 10.

public class MyComparer : IComparer<string> {

    [DllImport("shlwapi.dll", CharSet=CharSet.Unicode, ExactSpelling=true)]
    static extern int StrCmpLogicalW(String x, String y);

    public int Compare(string x, string y) {
        return StrCmpLogicalW(x, y);
    }

}

Array.Sort(unsortedNames, new MyComparer());

And since I just noticed the question is tagged VB... Forgive my rusty VB!

Public Class MyComparer
    Implements IComparer(Of String)

    Declare Unicode Function StrCmpLogicalW Lib "shlwapi.dll" ( _
        ByVal s1 As String, _
        ByVal s2 As String) As Int32

    Public Function Compare(Byval x as String, Byval y as String) As Integer _
        Implements System.Collections.Generic.IComparer(Of String).Compare

        Return StrCmpLogicalW(x, y)

    End Function

End Class

Josh Einstein 2010-06-23 07:20:00

Wow .... works really well ... thanks Josh ! ...Just one concern though ... what I'm working on will be sold as a part of a product. Now will this library be available on all servers running ASP.Net 2.0+ .. sorry if the question sounds stupid. Just wanted to make sure I won't run into problems in cases where this library is not available. Is it possible to check if this library exists and then apply the sorting ... and skip if it doesn't exist.Thank you so much Josh ... would've taken me years to figure this one out by myself.

Norman 2010-06-23 07:58:26

According to the doc page it's supported on XP and up, and Server 2003 and up. For down-level platforms I suppose you could swap in an implementation that resorted to plain alpha sorting.

Josh Einstein 2010-06-23 08:02:18

There was a small problem in the code (possibly because of conversion to VB) Line 8 works if it is ;Public Function Compare(ByVal x As String, ByVal y As String) As Integer Implements System.Collections.Generic.IComparer(Of String).Compare--- Is there a way to check if the library exists? Ignore if you think this was a stupid questionThanks,Norman.

Norman 2010-06-23 08:23:13

Sorry Norman I wasn't trying to ignore. I think you can use the GetProcAddress API to determine if the function exists but I'm not really a PInvoke expert. Thanks for the heads up about the glitch in the VB snippet. I'll update it.

Josh Einstein 2010-06-26 14:47:20

ansaurus

tags:

views:

answers:

Sorting an array of folder names like Windows Explorer (Numerically and Alphabetically) - VB.NET

related questions