XmlDataDocument Events Working in VB.NET
In this article I will explain working with XmlDataDocument Events in ADO.NET.
The XmlDataDocument events are useful when your application needs to notify you when changes are being made to an XmlDataDocument object. XmlDocument defines XmlDataDocument events (see Table 9-6).
Table 9-6. XmlDataDocument Events
|
EVENT
|
DESCRIPTION
|
|
NodeChanged
|
Occurs when the value of a node has been changed
|
|
NodeChanging
|
Occurs when the value of a node is changing
|
|
NodeInserted
|
Occurs when a node inserted into another node
|
|
NodeInserting
|
Occurs when a node inserting to another node
|
|
NodeRemove
|
Occurs when a node has been removed
|
|
NodeRemoving
|
Occurs when a node is being removed
|
The XmlNodeChangedEventHandler method handles the events listed in Table 9-6. The XmlNodeChangedEventHandler is as follows:
Public Delegate Sub XmlNodeChangedEventHandler(ByVal senderAs Object,ByVal e As XmlNodeChangedEventArgs)
Where sender is the source of the event and e is an XmlNodeChangedEventArgs that contains the event
data
. XmlNodeChangedEventArgs defines properties (see Table 9-7).
|
PROPERTY
|
DESCRIPTION
|
|
Action
|
Returns a value indicating the type of node changed event
|
|
NewParent
|
Returns a value of parent node after the operation is finished
|
|
Node
|
Returns the node that is being added, removed, or changed
|
|
OldParent
|
Returns the value of the parent node before operation started
|
Listing 9-11. Handles XmlDataDocument events. The XmlDocumentBtn_Click method creates event handlers for the NodeChanged, NodeInserted, and NodeRemoved events. The MyNodeChangedEvent, MyNodeInsertEvent, and MyNodeRemoved event handlers execute when these events fire. I used LoadXml to load an XML fragment and then used the ReplaceChild and RemoveChild methods to replace and remove document nodes.
Listing 9-11. The XmlDataDocument event handling sample
Private Sub XmlDocumentBtn_Click(ByVal sender As Object,ByVal e As System.EventArgs)
Dim xmlDoc As New XmlDocument()
xmlDoc.LoadXml("<Record> Some Value </Record>")
' Create the event handlers.
AddHandler xmlDoc.NodeChanged,AddressOf Me.MyNodeChangedEvent
AddHandler xmlDoc.NodeInserted,AddressOf Me.MyNodeInsertedEvent
AddHandler xmlDoc.NodeRemoved,AddressOf Me.MyNodeRemovedEvent
Dim root As XmlElement = xmlDoc.DocumentElement
Dim str As String = root.ToString()
Dim xmlDocFragmentAs XmlDocumentFragment = xmlDoc.CreateDocumentFragment()
xmlDocFragment.InnerXml = "<Fragment><SomeDate>Fragment Data</SomeDate></Fragment>"
' Replace Node
Dim rootNodeAs XmlElement = xmlDoc.DocumentElement
rootNode.ReplaceChild(xmlDocFragment, rootNode.LastChild)
'Remove Node
Dim nodeAs XmlNode = xmlDoc.LastChild
xmlDoc.RemoveChild(node)
End Sub
Listing 9-12. Shows the NodeChangedEvent handler. The Node property of XmlNodeChangedEventArgs returns XmlNode. Using the Node property you can get more information about a node such as its parent node, value, name, namespace, and so on.
Listing 9-12. The NodeChanged event handler
Public Sub MyNodeChangedEvent(ByVal srcAs Object,ByVal args As XmlNodeChangedEventArgs)
MessageBox.Show("Node Changed Event Fired for node " & args.Node.Name)
If args.Node.ValueIsNot Nothing Then
MessageBox.Show(args.Node.Value)
End If
End Sub
Similar to listing 9-12, Listing 9-13 and 9-14 show event handlers for the NodeInserted and NodeRemoved events.
Listing 9-13. The NodeInserted event handler
Public Sub MyNodeInsertedEvent(ByVal src As Object,ByVal args As XmlNodeChangedEventArgs)
MessageBox.Show("Node Inserted event fired for node " & args.Node.Name)
If args.Node.Value IsNot Nothing Then
MessageBox.Show(args.Node.Value)
End If
End Sub
Listing 9-14.The NodeRemoved event handler
Public Sub MyNodeRemovedEvent(ByVal src As Object,ByVal args As XmlNodeChangedEventArgs)
MessageBox.Show("Node Removed event fired for node " & args.Node.Name)
If args.Node.ValueIsNot Nothing Then
MessageBox.Show(args.Node.Value)
End If
End Sub
Conclusion
Hope this article would have helped you in understanding working with XmlDataDocument Events in ADO.NET. See other articles on the website also for further reference.