TreeListView.NodeExpanding Event

Occurs before a node is expanded.

Namespace: DevExpress.Xpf.Grid

Assembly: DevExpress.Xpf.Grid.v21.1.dll


public event TreeListNodeAllowEventHandler NodeExpanding

Event Data

The NodeExpanding event's data class is TreeListNodeAllowEventArgs. The following properties provide information specific to this event:

Property Description
Allow Gets or sets whether the operation is allowed.
Handled Gets or sets a value that indicates the present state of the event handling for a routed event as it travels the route. Inherited from RoutedEventArgs.
Node Gets the processed node. Inherited from TreeListNodeEventArgs.
OriginalSource Gets the original reporting source as determined by pure hit testing, before any possible Source adjustment by a parent class. Inherited from RoutedEventArgs.
RoutedEvent Gets or sets the RoutedEvent associated with this RoutedEventArgs instance. Inherited from RoutedEventArgs.
Row Gets the processed row. Inherited from TreeListNodeEventArgs.
Source Gets or sets a reference to the object that raised the event. Inherited from RoutedEventArgs.

The event data class exposes the following methods:

Method Description
InvokeEventHandler(Delegate, Object) When overridden in a derived class, provides a way to invoke event handlers in a type-specific way, which can increase efficiency over the base implementation. Inherited from RoutedEventArgs.
OnSetSource(Object) When overridden in a derived class, provides a notification callback entry point whenever the value of the Source property of an instance changes. Inherited from RoutedEventArgs.


Handle this event to:

  • Cancel the action by setting the event parameter’s TreeListNodeAllowEventArgs.Allow property to false;
  • Dynamically create child nodes. In this instance, when expanding a node, you do not know whether it has child nodes or not. If the node has no child nodes, hide the expand button by setting the TreeListNode.IsExpandButtonVisible property to false.

After a node has been expanded, the TreeListView.NodeExpanded event is raised.

To learn more, see Expanding and Collapsing Nodes .


In this example, the TreeListView displays the file/folder tree. Child nodes that correspond to sub folders or files contained within a folder are dynamically created when a parent node is being expanded.

View Example

<Window x:Class="DynamicNodeLoading.MainWindow"
        Title="MainWindow" Height="350" Width="525" xmlns:dxg="">
        <dxg:GridControl Name="grid">
                <dxg:GridColumn FieldName="Name" />
                <dxg:GridColumn FieldName="ItemType" />
                <dxg:GridColumn FieldName="Size" />
                <dxg:GridColumn FieldName="FullName" />
                <dxg:TreeListView Name="treeListView1" AutoWidth="True"
See Also