Custom class inherits DictionaryBase

[Nick]

I am writing an application that uses a custom class which inherits
DictionaryBase so that I can add items with an associated key. When I try to
serialize the object though, I get the following error: The type
BuildingsCollection is not supported because it implements IDictionary. Here
is my class:

Namespace BusinessLogicLayer

<Serializable()> _
Public Class BuildingsCollection
Inherits DictionaryBase

Default Property Item(ByVal key As String) As Building
Get
Return Me.Dictionary.Item(key)
End Get
Set(ByVal Value As Building)
Me.Dictionary.Item(key) = Value
End Set
End Property

Public Sub Add(ByVal item As Building, ByVal key As String)
Dictionary.Add(key, item)
End Sub

Public Function Contains(ByVal key As String) As Boolean
Return Dictionary.Contains(key)
End Function

Public ReadOnly Property Keys() As ICollection
Get
Return Dictionary.Keys
End Get
End Property

Public ReadOnly Property Values() As ICollection
Get
Return Dictionary.Values
End Get
End Property

Public Sub Remove(ByVal key As String)
Me.Dictionary.Remove(key)
End Sub

End Class

End Namespace

Do I have to do anything special to it to allow me to serialize to XML? The
Building object seen in the class is just what I want my collection to be of
so other objects will not work. The building class will work with
serialization. In my main app I have a "Person" class defined with the
following: Private pBuildings as BuildingsCollection, since one person could
have more than one building.

Thanks in advance...

- Nick

[Kevin Yu [MSFT]]

Hi,

First of all, I would like to confirm my understanding of your issue. From
your description, I understand that you're trying to serialize a Collection
object into Xml and get a NotSupportedException. If there is any
misunderstanding, please feel free to let me know.

One of the problems will be that the serialization/deserialization does not
preserve identity, so the keys of the deserialized IDictionary will not
match the original. This is because they will be constructed anew.

Also, XmlSerialization is schema driven, and XmlSerializer will attempt to
infer schema from the given type, however there is no obvious way to infer
schema from IDictionary: it is not strongly typed. A strongly typed
collection that is explicitly stated the type of object it collects.

Moreover, XmlSerializer serializes by reflecting public properties. It
doesn't use the SerializableAttribute/ISerializable framework. IDictionary
doesn't expose each element as a public property, so it can't get at the
items that are contained inside. Also, indexed properties can not be stored
either, because they require the serializer to know all of the keys, which
it can not.

A workaround would be wrap your IDictionary in a class that
serializes/deserializes it into a name/value pair array or a jagged object
array with 2 dimensions or some other convenient structure. In the client,
you can deserialize the object back into something that implements
IDictionary. Your wrapper class only needs to wrap IDictionary, for
serialization.

HTH.

Kevin Yu
=======
"This posting is provided "AS IS" with no warranties, and confers no
rights."

[Kevin Yu [MSFT]]

Hi,

First of all, I would like to confirm my understanding of your issue. From
your description, I understand that you're trying to serialize a Collection
object into Xml and get a NotSupportedException. If there is any
misunderstanding, please feel free to let me know.

One of the problems will be that the serialization/deserialization does not
preserve identity, so the keys of the deserialized IDictionary will not
match the original. This is because they will be constructed anew.

Also, XmlSerialization is schema driven, and XmlSerializer will attempt to
infer schema from the given type, however there is no obvious way to infer
schema from IDictionary: it is not strongly typed. A strongly typed
collection that is explicitly stated the type of object it collects.

Moreover, XmlSerializer serializes by reflecting public properties. It
doesn't use the SerializableAttribute/ISerializable framework. IDictionary
doesn't expose each element as a public property, so it can't get at the
items that are contained inside. Also, indexed properties can not be stored
either, because they require the serializer to know all of the keys, which
it can not.

A workaround would be wrap your IDictionary in a class that
serializes/deserializes it into a name/value pair array or a jagged object
array with 2 dimensions or some other convenient structure. In the client,
you can deserialize the object back into something that implements
IDictionary. Your wrapper class only needs to wrap IDictionary, for
serialization.

HTH.

Kevin Yu
=======
"This posting is provided "AS IS" with no warranties, and confers no
rights."