Persistence of Classes

[honeybee]

I want to create a COM for my project which has one creatable class and more subclasses which are not creatable, all of them being public.

Class Parent:  Public/Creatable
   |
   |---- Class Child1     Public/Not Creatable
   |             |
   |             |---- Class Child2     Public/Not Creatable

The hierarchy operates somewhat like the ListView control, where the ListItems collection exposes the ListItem objects. The Parent class will have a collection that stores Child1 class objects, and each Child1 class will have a collection that holds the Child2 objects.

Since the Persistable property is available only for public creatable classes, I can use this property only for the Parent class. But I actually want to store the properties of the Child1 and Child2 classes.

Any ideas?

.

[Edneeis]

You can use a property bag to easily write the data to disk and persist it that way.

[honeybee]

No, you didn't get the question or I was not clear enough.

I know how I can persist a class, but I am facing a problem. The classes which I want to persist are PublicNotCreatable. Since a class has to be public and creatable in order to be persistable, I cannot directly make these classes persist.

.

[Edneeis]

Can't you just have the parent that is creatable Load/Save the Non Createable classes?

[honeybee]

And how can I do that? Unless the child classes are persistable, I cannot use the PropertyBag object in them, can I?

I have an idea: In my Parent class, I have a property which is a collection of Child1 objects:

Parent.Child1Objects

If I make the Parent class persistable, do you think it would allow me to save this property, and in turn the objects in the collection Child1Objects be saved?

.

[Edneeis]

I've never actually used the Persistable property of a class before. Hardly ever have to persist a class unless it is saving the data to some form of media. BUT does the Persistable property actually do the work of persisting the object or just give you the extra Events like a control to have you do it yourself (i.e. InitProperties, Read/WriteProperties)?

Also you can use a propertybag anywhere so if it turns out that is what you need to do then it'll work fine. You could do it pretty much just like a control using the events that the Public class gives you since its persistable.

[honeybee]

In an ActiveX control, you can use the PropertyBag almost all the time. Not so in ordinary classes.

Also I think you need the ReadProperties, WriteProperties methods and the PropertyChanged event to be available in your class, for which it has to be publicly creatable, which an ActiveX "control" is.

.

[Edneeis]

Although a PropertyBag is used a lot in controls it can be used anywhere, its just another object. I use it all the time to serialize objects. Also since the Parent class is persistable you can use its Read/Write events and the property bag to serialize and persist the items in the collections. You would do it pretty much just like an activeX control, only you may need to store the data somewhere between uses (i.e. a file, database, registry, etc...)

Even without the class being persistable you can use the Initialize and Terminate events if you need to.

If you need code for the property bag part then let me know but it works the same as when it is used in an activeX control only you want to store the PropertyBag.Contents somewhere. If you try it I bet it'll work.

[LucianoBraatz]

I had a situation like that previously and solved making a loop inside the subclasses' objects and writing the their properties in the parent class PropertyBag.

Private Sub UserControl_WriteProperties(ByRef PBag As PropertyBag)
Dim Index1 as Integer,Index2 as Integer
With PBag
        'First save the Parent class properties 
        .WriteProperty "Property1",Property1
             .
        .WriteProperty "Propertyn",Propertyn
        'Then save the ChildClass1 collection object's number 
        .WriteProperty "ChildClass1Count",ChildClass1.Count
        For Index1=1 To ChildClass1.Count
                 'Save the properties of each Object in the ChildClass1 Collection 
                .WriteProperty "ChildClass1[" & Index1 & "]Property1",ChildClass1(Index1).Property1
                     .
                .WriteProperty "ChildClass1[" & Index1 & "]Propertyn",,ChildClass1(Index1).Propertyn
                 'Then save the ChildClass2 collection object's number of the current object in ChildClass1 collection
                .WriteProperty "ChildClass1[" & Index1 & "].ChildClass2Count",ChildClass1(Index1).ChildClass2.Count
                For Index2=1 To ChildClass2.Count
                         'Save the properties of each Object in the ChildClass2 Collection of the current object in ChildClass1 collection
                        .WriteProperty "ChildClass1[" & Index1 & "]ChildClass2[" & Index2 & "]Property1",ChildClass2(Index1).ChildClass2(Index2).Property1
                             .
                        .WriteProperty "ChildClass1[" & Index1 & "]ChildClass2[" & Index2 & "]Propertyn",ChildClass1(Index1).ChildClass2(Index2).Propertyn
                Next Index2
        Next Index1
End With
End Sub
 
Private Sub UserControl_ReadProperties(ByRef PBag As PropertyBag)
Dim Index1 as Integer,Index2 as Integer
Dim Max1 as Integer, Max2 as Integer
Dim oCCO1 as ChildClassObject1,oCCO2 as ChildClassObject2
With PBag
        'First read the Parent class properties 
        Property1=.ReadProperty("Property1")
                  .
        Propertyn=.ReadProperty("Propertyn")
        'Then get the ChildClass1 collection object's number into Max1 variable
        Max1=.ReadProperty("ChildClass1Count")
        'Clears the ChildClass1 properties
        Set ChildClass1=Nothing
        Set ChildClass1 = New ChildClass1
        For Index1=1 To Max1
                'Create a object contained in ChildClass1 Collection
                Set oCCO1=New ChildClassObject1
                'Reads its properties
                oCCO1.Property1=.ReadProperty("ChildClass1[" & Index1 & "]Property1")
                     .
                oCCO1.Propertyn=.ReadProperty("ChildClass1[" & Index1 & "]Propertyn")
                'Then get the ChildClass2 collection object's number for current object "oCCO1" into Max2 variable
                Max2=.ReadProperty("ChildClass1[" & Index1 & "].ChildClass2Count")
                'Clears the ChildClass2 collection inside oCCO1
                Set oCCO1.ChildClass2=Nothing
                Set oCCO1.ChildClass2=New ChildClass2
                For Index2=1 To Max2
                        'Create a object contained in ChildClass2 Collection
                        Set oCCO2= New ChildClassObject2
                        'Reads its properties  
                        oCCO2.Property1=.ReadProperty("ChildClass1[" & Index1 & "]ChildClass2[" & Index2 & "]Property1")
                             .
                        oCCO2.Propertyn=.ReadProperty("ChildClass1[" & Index1 & "]ChildClass2[" & Index2 & "]Propertyn")
                        'Save the object in ChildClass2 inside oCCO1
                        oCCO1.ChildClass2.AddObject oCCO2
                Next Index2
                'Save the object in ChildClass1 
                ChildClass1.AddObject oCCO1
        Next Index1
End With
End Sub