Collection Class

[Doug Bulmer]

Can anyone point out what is wrong with the following code. I add 3 container objects to the ship object. When I try to get any container object back from the ship object it always returnd the last container object that was added.

Thanks

'PBWIN 9.00 - WinApi 05/2008 - XP Pro SP3
'OOP example by Steve Pringles
' ======================================================================================================
CLASS cContainer
  INSTANCE m_Width    AS SINGLE
  INSTANCE m_Length   AS SINGLE
  INSTANCE m_height   AS SINGLE
  INTERFACE iContainer
    INHERIT IDISPATCH
    PROPERTY GET WIDTH () AS SINGLE
      PROPERTY = m_Width
    END PROPERTY
    PROPERTY SET WIDTH (BYVAL Value AS SINGLE)
      m_Width = Value
    END PROPERTY
    PROPERTY GET Length() AS SINGLE
      PROPERTY = m_Length
    END PROPERTY
    PROPERTY SET Length(BYVAL Value AS SINGLE)
      m_Length = Value
    END PROPERTY
    PROPERTY GET Height() AS SINGLE
      PROPERTY = m_Height
    END PROPERTY
    PROPERTY SET Height(BYVAL Value AS SINGLE)
      m_Height = Value
    END PROPERTY
  END INTERFACE
END CLASS

CLASS cShip
  INSTANCE m_ContainerCount   AS WORD
  INSTANCE m_Volume           AS SINGLE
  INSTANCE m_VolumeUsed       AS SINGLE
  INSTANCE m_Containers()     AS iContainer
  CLASS METHOD CREATE()
    REDIM m_Containers(0) AS INSTANCE iContainer
  END METHOD
  INTERFACE iShip
    INHERIT IDISPATCH
    METHOD SetMaxSize(BYVAL nLength AS SINGLE, BYVAL nWidth AS SINGLE, BYVAL nHeight AS SINGLE)
      m_Volume = nLength * nWidth * nHeight
    END METHOD
    METHOD AddContainer(BYVAL iC AS iContainer) AS LONG
      LOCAL ContainerVolume AS SINGLE
      IF ISOBJECT(iC) THEN
        IF IC.Width AND iC.Height AND iC.Length THEN
          ContainerVolume = iC.Width * iC.Height * iC.Length
          IF ContainerVolume + m_VolumeUsed <= m_Volume THEN
            INCR m_ContainerCount
            REDIM PRESERVE m_Containers(m_ContainerCount - 1) AS INSTANCE iContainer
            m_Containers(m_ContainerCount - 1) = iC
            m_VolumeUsed = m_VolumeUsed + ContainerVolume
            METHOD = 1
          ELSE
            METHOD = 0
          END IF
        END IF
      END IF
    END METHOD
    METHOD GetVolumeUsed() AS SINGLE
      METHOD = m_VolumeUsed
    END METHOD
    METHOD GetCapacityLeft() AS SINGLE
      METHOD = m_Volume - m_VolumeUsed
    END METHOD
    METHOD GetContainerCount() AS WORD
      METHOD = m_ContainerCount
    END METHOD
    METHOD GetContainer(BYVAL nItem AS WORD) AS iContainer
      IF nItem > 0 AND nItem <= m_ContainerCount THEN
        METHOD = m_Containers(nItem - 1)
      ELSE
        METHOD = NOTHING
      END IF
    END METHOD
  END INTERFACE
END CLASS

FUNCTION PBMAIN() AS LONG
  LOCAL cCont  AS iContainer
  LOCAL cBoat  AS iShip
  LOCAL s$
  cBoat = CLASS "cShip"
  cCont = CLASS "cContainer"
  cBoat.SetMaxSize(20, 20, 40)

  cCont.Length = 1
  cCont.Width  = 1
  cCont.Height = 1
  cBoat.AddContainer(cCont)

  cCont.Length = 2
  cCont.Width  = 2
  cCont.Height = 2
  cBoat.AddContainer(cCont)

  cCont.Length = 3
  cCont.Width  = 3
  cCont.Height = 3
  cBoat.AddContainer(cCont)
  
  s$ =  "Str$(cBoat.GetContainerCount()) = " & STR$(cBoat.GetContainerCount()) & $CRLF

  cCont = cBoat.GetContainer(1)
  s$ = s$ & "Volume used  : " & FORMAT$(cBoat.GetVolumeUsed) & " square feet" & $CRLF
  s$ = s$ & "Capacity left: " & FORMAT$(cBoat.GetCapacityLeft) & " square feet" & $CRLF
  s$ = s$ & "Width of first container = " & FORMAT$(cCont.Width) & $CRLF

  cCont = cBoat.GetContainer(2)
  s$ = s$ & "Width of Second container = " & FORMAT$(cCont.Width) & $CRLF

  cCont = cBoat.GetContainer(3)
  s$ = s$ & "Width of Third container = " & FORMAT$(cCont.Width) & $CRLF

  ?s$
  
END FUNCTION

[Charles Dietz]

How about this, Doug?

FUNCTION PBMAIN() AS LONG
  LOCAL cCont, cCont1, cCont2, cCont3  AS iContainer
  LOCAL cBoat  AS iShip
  LOCAL cContArr() AS iContainer
  LOCAL s$
  cBoat = CLASS "cShip"
  cCont = CLASS "cContainer"
  cBoat.SetMaxSize(20, 20, 40)
  
  cCont1 = CLASS "cContainer"
  cCont1.Length = 1
  cCont1.WIDTH  = 1
  cCont1.Height = 1
  cBoat.AddContainer(cCont1)
  
  cCont2 = CLASS "cContainer"
  cCont2.Length = 2
  cCont2.WIDTH  = 2
  cCont2.Height = 2
  cBoat.AddContainer(cCont2)
  
  cCont3 = CLASS "cContainer"
  cCont3.Length = 3
  cCont3.WIDTH  = 3
  cCont3.Height = 3
  cBoat.AddContainer(cCont3)
  ...
  ...

[Doug Bulmer]

The AddContainer method is BYVAL but is acting like BYREF

    METHOD AddContainer(BYVAL iC AS iContainer) AS LONG

Also if I recreate that container object between each add it seems to correct the problem.

 LOCAL cCont  AS iContainer
  LOCAL cBoat  AS iShip
  LOCAL s$
  cBoat = CLASS "cShip"
  cBoat.SetMaxSize(20, 20, 40)

  cCont = CLASS "cContainer"
  cCont.Length = 1
  cCont.Width  = 1
  cCont.Height = 1
  cBoat.AddContainer(cCont)
  cCont = NOTHING
  
  cCont = CLASS "cContainer"
  cCont.Length = 2
  cCont.Width  = 2
  cCont.Height = 2
  cBoat.AddContainer(cCont)
  cCont = NOTHING

  cCont = CLASS "cContainer"
  cCont.Length = 3
  cCont.Width  = 3
  cCont.Height = 3
  cBoat.AddContainer(cCont)
  cCont = NOTHING

  cCont = CLASS "cContainer"

[colin glenn]

Think you might be solving your issue like that, seems that as long as the "parent" object is in existence, any "siblings" or "clones" are connected to the parent, changing the properties of the parent affect the children. When you "destroy" the parent, the reference to the parent is lost by the child and the child becomes independent.

[Steven Pringels 3]

Let me also emphasize that this is not a true collection class since you can only store one particular interface type whereas a true collection doesn't bother with the interface type.