xmlserializer and IDIctionary

[Chris Hickman]

Hello,

I wrote this code a while back to solve the problem of serializing
hashtables that can hold complex types (as long as you know what types
it may hold ahead of time).

Public Class SerializableHashtable
Inherits System.Collections.Hashtable
Implements IXmlSerializable

Private _EntrySerializer As XmlSerializer

Public Sub New()
Dim HashInfo As System.Reflection.MemberInfo = Me.GetType
Dim InclAttrs As XmlIncludeAttribute() =
CType(HashInfo.GetCustomAttributes(GetType(XmlIncl udeAttribute),
True), XmlIncludeAttribute())
Dim InclTypes(InclAttrs.Length - 1) As Type
For idx As Integer = 0 To InclAttrs.Length - 1
InclTypes(idx) = InclAttrs(idx).Type
Next
_EntrySerializer = New XmlSerializer(GetType(HashEntry),
InclTypes)
End Sub

Public Sub WriteXml(ByVal writer As System.Xml.XmlWriter)
Implements System.Xml.Serialization.IXmlSerializable.WriteXml
For Each key As Object In MyBase.Keys
Dim entry As New HashEntry
entry.Key = key
entry.Value = Me.Item(key)
_EntrySerializer.Serialize(writer, entry)
Next
End Sub

Public Sub ReadXml(ByVal reader As System.Xml.XmlReader)
Implements System.Xml.Serialization.IXmlSerializable.ReadXml
' skip empty node
If reader.IsEmptyElement = True Then
reader.Read()
Return
End If

' skip start tag
reader.Read()
reader.MoveToContent()
While ((Not reader.EOF) AndAlso (reader.Name = "HashEntry"))
Dim entry As HashEntry =
CType(_EntrySerializer.Deserialize(reader), HashEntry)
Me.Add(entry.Key, entry.Value)
reader.MoveToContent()
End While
reader.ReadEndElement()
End Sub

Public Function GetSchema() As System.Xml.Schema.XmlSchema
Implements System.Xml.Serialization.IXmlSerializable.GetSchem a
Return Nothing
End Function

Class HashEntry
Public Key As Object
Public Value As Object
End Class

End Class
To make use of it simply derive your new type from it and mark it with
xmlincludes() for any types it may hold...
<XmlInclude(GetType(SomeClass), XmlInclude(GetType(SomeOtherClass))> _
Public Class ExampleHashTable
Inherits Utility.SerializableHashtable
End Class

Feel free to use/modify for your own purposes. Please share if you can
improve it.

[Alex Maghen]

Chris -

Hi. I'm pretty much exclusively a C# guy and I'm trying to do something that I thought would be really simple - XMLSerialize a Hashtable. I'm getting a runtime "Reflection" error. The class I'm trying to serialize is nothing but two string members and one hashtable (all Public). And I get this error even when the Hashtable hasn't even been populated.

Ideas?

"Chris Hickman" wrote:

Hello,

I wrote this code a while back to solve the problem of serializing
hashtables that can hold complex types (as long as you know what types
it may hold ahead of time).

Public Class SerializableHashtable
Inherits System.Collections.Hashtable
Implements IXmlSerializable

Private _EntrySerializer As XmlSerializer

Public Sub New()
Dim HashInfo As System.Reflection.MemberInfo = Me.GetType
Dim InclAttrs As XmlIncludeAttribute() =
CType(HashInfo.GetCustomAttributes(GetType(XmlIncl udeAttribute),
True), XmlIncludeAttribute())
Dim InclTypes(InclAttrs.Length - 1) As Type
For idx As Integer = 0 To InclAttrs.Length - 1
InclTypes(idx) = InclAttrs(idx).Type
Next
_EntrySerializer = New XmlSerializer(GetType(HashEntry),
InclTypes)
End Sub

Public Sub WriteXml(ByVal writer As System.Xml.XmlWriter)
Implements System.Xml.Serialization.IXmlSerializable.WriteXml
For Each key As Object In MyBase.Keys
Dim entry As New HashEntry
entry.Key = key
entry.Value = Me.Item(key)
_EntrySerializer.Serialize(writer, entry)
Next
End Sub

Public Sub ReadXml(ByVal reader As System.Xml.XmlReader)
Implements System.Xml.Serialization.IXmlSerializable.ReadXml
' skip empty node
If reader.IsEmptyElement = True Then
reader.Read()
Return
End If

' skip start tag
reader.Read()
reader.MoveToContent()
While ((Not reader.EOF) AndAlso (reader.Name = "HashEntry"))
Dim entry As HashEntry =
CType(_EntrySerializer.Deserialize(reader), HashEntry)
Me.Add(entry.Key, entry.Value)
reader.MoveToContent()
End While
reader.ReadEndElement()
End Sub

Public Function GetSchema() As System.Xml.Schema.XmlSchema
Implements System.Xml.Serialization.IXmlSerializable.GetSchem a
Return Nothing
End Function

Class HashEntry
Public Key As Object
Public Value As Object
End Class

End Class
To make use of it simply derive your new type from it and mark it with
xmlincludes() for any types it may hold...
<XmlInclude(GetType(SomeClass), XmlInclude(GetType(SomeOtherClass))> _
Public Class ExampleHashTable
Inherits Utility.SerializableHashtable
End Class

Feel free to use/modify for your own purposes. Please share if you can
improve it.

[fritz]

Alex Maghen wrote:

Chris -

Hi. I'm pretty much exclusively a C# guy and I'm trying to do something
that I thought would be really simple - XMLSerialize a Hashtable. I'm
getting a runtime "Reflection" error. The class I'm trying to serialize is
nothing but two string members and one hashtable (all Public). And I get
this error even when the Hashtable hasn't even been populated.

Ideas?

"Chris Hickman" wrote:

Hello,

I wrote this code a while back to solve the problem of serializing
hashtables that can hold complex types (as long as you know what types
it may hold ahead of time).

Public Class SerializableHashtable
Inherits System.Collections.Hashtable
Implements IXmlSerializable

Private _EntrySerializer As XmlSerializer

Public Sub New()
Dim HashInfo As System.Reflection.MemberInfo = Me.GetType
Dim InclAttrs As XmlIncludeAttribute() =
CType(HashInfo.GetCustomAttributes(GetType(XmlIncl udeAttribute),
True), XmlIncludeAttribute())
Dim InclTypes(InclAttrs.Length - 1) As Type
For idx As Integer = 0 To InclAttrs.Length - 1
InclTypes(idx) = InclAttrs(idx).Type
Next
_EntrySerializer = New XmlSerializer(GetType(HashEntry),
InclTypes)
End Sub

Public Sub WriteXml(ByVal writer As System.Xml.XmlWriter)
Implements System.Xml.Serialization.IXmlSerializable.WriteXml
For Each key As Object In MyBase.Keys
Dim entry As New HashEntry
entry.Key = key
entry.Value = Me.Item(key)
_EntrySerializer.Serialize(writer, entry)
Next
End Sub

Public Sub ReadXml(ByVal reader As System.Xml.XmlReader)
Implements System.Xml.Serialization.IXmlSerializable.ReadXml
' skip empty node
If reader.IsEmptyElement = True Then
reader.Read()
Return
End If

' skip start tag
reader.Read()
reader.MoveToContent()
While ((Not reader.EOF) AndAlso (reader.Name = "HashEntry"))
Dim entry As HashEntry =
CType(_EntrySerializer.Deserialize(reader), HashEntry)
Me.Add(entry.Key, entry.Value)
reader.MoveToContent()
End While
reader.ReadEndElement()
End Sub

Public Function GetSchema() As System.Xml.Schema.XmlSchema
Implements System.Xml.Serialization.IXmlSerializable.GetSchem a
Return Nothing
End Function

Class HashEntry
Public Key As Object
Public Value As Object
End Class

End Class
To make use of it simply derive your new type from it and mark it with
xmlincludes() for any types it may hold...
<XmlInclude(GetType(SomeClass), XmlInclude(GetType(SomeOtherClass))> _
Public Class ExampleHashTable
Inherits Utility.SerializableHashtable
End Class

Feel free to use/modify for your own purposes. Please share if you can
improve it.

Problem here is that the hashcode are really not 'duplicable', they are
unique. So you must write your own ISerializable and your own deserialize
to build the Hashtable again!