Question Searching a generic list

[goldford]

Hi,

I have been reading extensively about searching generic lists in VB.NET with the usage of delegates. However, I still cannot seem to grasp how to achieve what I want to, which I believe is frustratingly simple!

I have a list populated with instances of an object with three parameters (fields/variables). When I receive a new object to add to the list I want to search the list for the "layer" field. If the field matches then I will replace that row (object) in the list with the new object, if no match is found then I will add it to the list.

My object:

Public Class LayertoAdd
Public Layer As String
Public QuanField As String
Public ClsField As String

Public Sub New(ByVal layer As String, ByVal QuanField As string, ByValClsField As String)

me.Layer = layer
Me.QuanField = QuanField
Me.ClsField = ClsField

End Sub
End Class

My List Variable:

Private m_LayersFields As List(Of LayerToAdd) = New List(Of LayerToAdd)

This list is going to be a property of the object. The property:

Public Property LHabParamList()

Get
Return m_LayersFields
End Get

Set (ByVal value)

Dim pLayerToAdd As LayerToAdd
pLayerToadd = value

 ' Here is where I am confused.  I just want a boolean return 
' true if the list contains a match in the .layer field of the LayerToAdd object
If m_LayersFields.Contains(...) = True Then
Else m_LayersFields.Add(pLayerToAdd)
End If

End Set
End Property

So I have not come up with the predicate function yet. I am stumped!

 

[TyB]

Possible useful link

This looks promising.

Usefulness of List.Find in VB.net

Ty

 

[MattP]

I would suggest you take a look at this link:

How to Use the Action and Predicate Delegates

Private pLayerToAdd As LayerToAdd
Private ListLayerToAdd As New List(Of LayerToAdd)

pLayerToAdd = New LayerToAdd("somevalue", "someothervalue", "anothervalue")
Dim idx As Integer = ListLayerToAdd.FindIndex(AddressOf FindByLayer)
If idx = -1 Then
     ListLayerToAdd.Add(pLayerToAdd)
Else
     ListLayerToadd.Item(idx) = pLayerToAdd
End If

Private Function FindByLayer(ByVal layer As LayerToAdd) As Boolean
     Return layer.Layer = pLayerToAdd.Layer
End Function

 

[goldford]

Thanks, Ty. That article was just what I was looking for.

Also, thx MattP. I had seen this article but will take a closer look at it in the coming days.