How To Detect Whether a New Symbol Or Shape Has Been Added / Removed From A Diagram

29 Feb 2016 / 2 minutes to read

You can make use of the Diagram.Model.EventSink.NodeCollectionChanged to detect whether a new node (symbol, shape or link) has been added/removed from a diagram. The event’s CollectionExEventArgs argument provides information about the node ensuing the add / remove operation.

The following code snippet updates a label with information on the type of the node that is added/deleted from the diagram.

diagram1.Model.EventSink.NodeCollectionChanged += new CollectionExEventHandler(EventSink_NodeCollectionChanged);

//ChildrenChangeComplete Event

//Update Label2 depending on whether a Shape is added or deleted from the Diagram

 private void EventSink_NodeCollectionChanged(CollectionExEventArgs evtArgs)

 {

	Node n = evtArgs.Element as Node;



	//ChangeType specifies whether the Collection change is Insertion/Removal

	if (evtArgs.ChangeType == CollectionExChangeType.Insert)

	{

		this.label2.ForeColor = Color.Blue;



		//Gets the Name of the inserted element

		this.label2.Text = "Last Node Added : " + n.Name.ToString();

	}

	else if (evtArgs.ChangeType == CollectionExChangeType.Remove)

	{

		this.label2.ForeColor = Color.Red;



		//Gets the Name of the removed element

		this.label2.Text = "Last Node Removed : " + n.Name.ToString();

	}

 }
EventSink.NodeCollectionChanged += new CollectionExEventHandler(EventSink_NodeCollectionChanged)

Me.Diagram1.Model.EventSink.NodeCollectionChanged+=New CollectionExEventHandler(EventSink_NodeCollectionChanged)

 'ChildrenChangeComplete Event

 'Update Label2 depending on whether a Shape is added or deleted from the Diagram

 Private Sub Model_ChildrenChangeComplete(ByVal evtArgs As CollectionExEventArgs)

	Dim n As Node = TryCast(evtArgs.Element, Node)

	'ChangeType specifies whether the Collection change is Insertion/Removal

	If evtArgs.ChangeType = CollectionExChangeType.Insert Then

		Me.label2.ForeColor = Color.Blue



		'Gets the Name of the inserted element

		Me.label2.Text = "Last Node Added: " + n.Name.ToString()

	ElseIf evtArgs.ChangeType = CollectionExChangeType.Remove Then

		Me.label2.ForeColor = Color.Red



		'Gets the Name of the removed element

		Me.label2.Text = "Last Node Removed: " + n.Name.ToString()

	End If

End Sub