VB.net how do I combine lists and classses? - vb.net

Question

Here are my definitions:
Public Class RouteDetails
Public strRoad As String
Public strToLane As String
Public strToDirection As String
End Class
Public Class Route
Public lstRouteDetails As List(Of RouteDetails)
End Class
ByVal lstRouteList As List(Of Route) (part of a function definition)
Sorry I tried to put the definitions section into a code block but, for some reason, it's not working.
Here is a section of the code, from that function, that I'm having problems with:
rlcRoute = New Route
lstRouteList.Add(rlcRoute)
rdcRouteStep.strRoad = sdrNextJunction.GetValue(3)
rdcRouteStep.strToLane = sdrNextJunction.GetValue(2)
rdcRouteStep.strToDirection = sdrNextJunction.GetValue(1)
For intloop = 0 To lstRouteList.Count - 1
lstRouteList(intloop).lstRouteDetails.Add(rdcRouteStep)
Next
The line, within the for loop, fails with:
System.NullReferenceException: 'Object reference not set to an
instance of an object.'
System.Collections.Generic.List.this[int].get.lstRouteDetails was
Nothing.
If I understand the error correctly then it's telling me that I haven't created an instance of lstRouteDetails for this instance of Route? If that's correct then I would
appreciate some advice on how to achieve this? I've tried a few combinations. The structure I'm trying to have is as follows:
RouteList is a list of objects of type route
Each Route object contains several objects of type RouteDetails
Thanks

Answer 1

You don't need a class for you list. You can just create one in your form.
I added a custom constructor to your class so you can set all the properties of the class in one line as demonstrated in the BuildList Sub. I had to add back the default constructor (no parameters). With the default constructor the properties are set individually. I also added an override of the .ToString method so we could use it in the Form. (See the OPCode method)
The Class
Public Class RouteDetails
Public strRoad As String
Public strToLane As String
Public strToDirection As String
Public Sub New()
End Sub
Public Sub New(Road As String, ToLane As String, Direction As String)
strRoad = Road
strToLane = ToLane
strToDirection = Direction
End Sub
Public Overrides Function ToString() As String
Return $"Road is {strRoad}, Lane is {strToLane}, Direction is {strToDirection}"
End Function
End Class
The Form
Private RouteList As New List(Of RouteDetails)
Private Sub BuildList_Click(sender As Object, e As EventArgs) Handles MyBase.Load
Dim Route As New RouteDetails()
Route.strRoad = "Main Street"
Route.strToLane = "Park Lane"
Route.strToDirection = "North East"
RouteList.Add(Route)
'or with the custom constructor
Dim Route2 As New RouteDetails("Wall Steet", "Mulberry Lane", "South West")
RouteList.Add(Route2)
End Sub
You can refer to the items in the list anywhere in the form.
Private Sub OPCode()
MessageBox.Show(RouteList(1).strToLane)
For Each item As RouteDetails In RouteList
ListBox1.Items.Add(item) 'The ListBox calls .ToString on the item for display
Next
End Sub
EDIT
Expanded Code
Public Class Route
Public RouteDetailsList As New List(Of RouteDetails)
Public Name As String
Public Sub New(RDL As List(Of RouteDetails), nme As String)
RouteDetailsList = RDL
Name = nme
End Sub
Public Sub New()
End Sub
Public Overrides Function ToString() As String
Return Name
End Function
End Class
To test the code
In the Form_Load call BuildRouteList
Private RouteList As New List(Of Route)
Private Sub BuildRouteList()
Dim Details = {New RouteDetails("MainStreet", "Park Lane", "North East"), New RouteDetails("Wall Steet", "Mulberry Lane", "South West")}
'Uses the construtor List(Of T)(IEnumerable<T>)
Dim R As New Route(New List(Of RouteDetails)(Details), "1")
RouteList.Add(R)
Dim Details2 = {New RouteDetails("Wall Street", "Strawberry Lane", "South West"), New RouteDetails("Pine Street", "Little Maid Lawnd", "North")}
Dim R2 As New Route(New List(Of RouteDetails)(Details2), "2")
RouteList.Add(R2)
End Sub
In a button click call OPCode1 (assumes a ListBox1 is present
Private Sub OPCode1()
MessageBox.Show(RouteList(0).RouteDetailsList(1).strToLane) 'shows Mulberry Lane
For Each item As Route In RouteList
ListBox1.Items.Add(item)
For Each route In item.RouteDetailsList
ListBox1.Items.Add(route) 'The ListBox calls .ToString on the item for display
Next
Next
End Sub