Best way to get the list of XML files

Question

I'm a newbie in the use of LinqToXml and I wonder if I can improve this snippet.

 Shared Function GetListByType(ByVal intIndex As Integer) As List(Of FileInfo)
 Dim strWorkingPath As DirectoryInfo = New DirectoryInfo(GetWorkspaceDir)
 Dim lstAllFiles As FileInfo() = strWorkingPath.GetFiles("*.xml", SearchOption.AllDirectories)
 Dim lstFiltredList As New List(Of FileInfo)
 Dim xelement As XElement
 Dim contratTypeIndex As String
 Dim contratVersion As Integer
 For Each fic In lstAllFiles
 xelement = xelement.Load(fic.FullName)
 contratTypeIndex = xelement.Element("TypeIndex").Value
 contratVersion = xelement.Element("Version").Value
 If (contratTypeIndex = intIndex.ToString And contratVersion = 0) Then
 lstFiltredList.Add(fic)
 End If
 Next
 Return lstFiltredList.Distinct.ToList
 End Function

Answer 1

Option Strict

You should always set Option Strict = On.

Short circuit evaluation

You should use the AndAlso operator instead of the And operator. By using And both conditions will be evaluated. By using AndAlso the second condition will only be evaluated if the first returns true.

List(Of FileInfo)

Instead of returning a List(Of FileInfo) you should consider to return an IEnumerable(Of FileInfo).

Naming

You shouldn't prefix your variables like strWorkingPath or lstAllFiles.

GetFiles() vs EnumerateFiles()

From the docs

The EnumerateFiles and GetFiles methods differ as follows: When you use EnumerateFiles, you can start enumerating the collection of names before the whole collection is returned; when you use GetFiles, you must wait for the whole array of names to be returned before you can access the array. Therefore, when you are working with many files and directories, EnumerateFiles can be more efficient.

Refactoring

First we will extract the loading of the file and reading the properties to separate methods and add a private class holding the TypeIndex and Version properties of the xml file.

Private Shared Function DoesFileMatch(file As FileInfo, index As String) As Boolean
 Dim version As XmlVersion = GetXmlVersion(file)
 Return (version.Version = "0" AndAlso version.TypeIndex = index)
End Function
Private Shared Function GetXmlVersion(file As FileInfo) As XmlVersion
 Return New XmlVersion(XElement.Load(file.FullName))
End Function
Private Class XmlVersion
 Public Property TypeIndex As String
 Public Property Version As String
 Public Sub New(element As XElement)
 TypeIndex = element.Element("TypeIndex").Value
 Version = element.Element("Version").Value
 End Sub
End Class

Next we add an overloaded GetListByType() method which takes a DirectoryInfo and a String as input parameter.

Shared Function GetListByType(directory As DirectoryInfo, ByVal typeIndex As String) As IEnumerable(Of FileInfo)
End Function

Which we call in our former method like

Shared Function GetListByType(ByVal typeIndex As Integer) As IEnumerable(Of FileInfo)
 Return GetListByType(typeIndex.ToString(), New DirectoryInfo(GetWorkspaceDir))
End Function 

The overloaded method can then be simplified, using all above, to

Private Shared Function GetListByType(directory As DirectoryInfo, ByVal typeIndex As String) As IEnumerable(Of FileInfo)
 Dim filteredFiles As New List(Of FileInfo)
 For Each fic In directory.EnumerateFiles("*.xml", SearchOption.AllDirectories)
 If (DoesFileMatch(fic, typeIndex)) Then
 filteredFiles.Add(fic)
 End If
 Next
 Return filteredFiles.Distinct()
End Function

But wait, we can do this a lot more lambda like

Private Shared Function GetListByType(directory As DirectoryInfo, ByVal typeIndex As String) As IEnumerable(Of FileInfo)
 Return directory.EnumerateFiles("*.xml", SearchOption.AllDirectories) _
 .Where(Function(x) DoesFileMatch(x, typeIndex)) _
 .Distinct()
End Function

Answer 2

I am impressed by the above answer but would like to add some minor things:

You should almost always set Option Infer On:

Private Shared Function DoesFileMatch(file As FileInfo, index As String) As Boolean
 Dim version = GetXmlVersion(file)
 Return version.Version = "0" AndAlso version.TypeIndex = index
End Function

Don't use unnecessary parentheses (that's for C# programmers).