Feeding Change events up a hierachy

[mandelbrot]

Dear All,

 

 

This is my first post in the forum, though I've posted loads of times in XVBT, so I'll make this a nice meaty one for the experts (I hope).

 

Presently, I have defined a data tree structure to hold diary information. The structure works something like:

 

Event (container)
|
+- Event (container)
|
+- Action (container)
|   |
|   +- Causality
|
+- Causality

 

Basically, each event can contain further events or an action or causality. Actions can only contain causalities.

 

Each object that changes invokes a change event. Each container that changes invokes a change event.

 

My problem is that I don't know how to promote change events up the hierachy :confused:. If anyone could point me in the right direction, I would really appreciate it.

 

 

Many thanks in advance,

Paul.

[Machaira]

Off the top of my head:

 

Each object could contain a Parent property that gets assigned when you create the object. Raise the Change event to the parent.

 

Am I missing something?

 

Here's some quick code:

 

Public Class BaseObject

   Private _parent As BaseObject
   Private _name As String
   Private _children As New Collection

   Public Property Parent() As BaseObject
       Get
           Return _parent
       End Get
       Set(ByVal Value As BaseObject)
           If _parent Is Nothing Then _parent = New BaseObject
           _parent = Value
       End Set
   End Property

   Public Property Name() As String
       Get
           Return _name
       End Get
       Set(ByVal Value As String)
           _name = Value
       End Set
   End Property

   Public Property Children()
       Get
           Return _children
       End Get
       Set(ByVal Value)

       End Set
   End Property

   Public Sub AddChild(ByVal child As Object)
       child.Parent = Me
       _children.Add(child)
   End Sub
   Public Sub Change()
       Debug.WriteLine("Change handled by BaseObject: " & Name)
   End Sub

End Class

Public Class EventObject
   Inherits BaseObject

   Public Shadows Sub Change()
       Debug.WriteLine("Change event handled by EventObject: " & Name)
       Me.Parent.Change()
   End Sub

End Class

Public Class ActionObject
   Inherits BaseObject

   Public Shadows Sub Change()
       Debug.WriteLine("Change event handled by ActionObject: " & Name)
       Me.Parent.Change()
   End Sub
End Class

Public Class CasualtyObject

   Private _parent As ActionObject
   Private _name As String

   Public Sub New()
       _parent = New ActionObject
   End Sub

   Public Property Parent() As ActionObject
       Get
           Return _parent
       End Get
       Set(ByVal Value As ActionObject)
           _parent = Value
       End Set
   End Property

   Public Property Name() As String
       Get
           Return _name
       End Get
       Set(ByVal Value As String)
           _name = Value
       End Set
   End Property

   Public Sub Change()
       Me.Parent.Change()
   End Sub
End Class

'test bed
       Dim obj As New EventObject
       Dim child As Object
       Dim child2 As Object

       obj.Name = "Parent"

       child = New EventObject
       CType(child, EventObject).Name = "Child 1"

       obj.AddChild(child)

       child = New ActionObject
       CType(child, ActionObject).Name = "Child 2"

       child2 = New CasualtyObject
       CType(child2, CasualtyObject).Name = "Child 3"

       child.AddChild(child2)
       obj.AddChild(child)

       CType(child2, CasualtyObject).Change()

Edited July 1, 2005 by Machaira

[mandelbrot]

I can see where you're coming from, Machaira, the only problem there is that, if branch C contains D, E and F, then even if one of the nodes fires a Change event, how does B, the parent of C know that the change event has been fired?

 

I suppose one option is to use the idea you have and include a reference to the ultimate parent - this would fire a change. It sounds a little messy, but it might work.

 

Trust me, Machaira - you know more than I at this stage! LOL!

 

 

Paul.

[mandelbrot]

Machaira,

 

 

I've just read the code you've added there - that does make sense. You've defied a base class that is inherited by each object...

 

I can see that working, after all, it's only the ultimate parent that needs to be referenced for change.

 

I'll give that a go, and see how it works!

 

Please accept my profuse thanks! :)

 

 

Paul.

[Machaira]

NP. Free free to post any follow-up if you have problems with it. I whipped it up in a few minutes so there might be some gotchas that develop. :)