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DxTreeView.BeforeCollapse Event

Fires when a node is about to be collapsed and allows you to cancel the action.

Namespace: DevExpress.Blazor

Assembly: DevExpress.Blazor.v23.2.dll

NuGet Package: DevExpress.Blazor


public Action<TreeViewNodeCancelEventArgs> BeforeCollapse { get; set; }

Event Data

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

Property Description
Cancel Specifies whether the action that raised the event should be canceled.
CausedByAPI Obsolete. Specifies whether an event was triggered by a user action or programmatically. Inherited from TreeViewNodeEventArgs.
NodeInfo Returns information about a node related to the event. Inherited from TreeViewNodeEventArgs.
Reason Returns the reason why the TreeView node’s state changes. Inherited from TreeViewNodeEventArgs.


The code sample below demonstrates how to prohibit root-level nodes from collapsing.

<DxTreeView BeforeCollapse="@BeforeCollapse">

@code  {
    void BeforeCollapse(TreeViewNodeCancelEventArgs e) {
        if (e.NodeInfo.Level == 0) e.Cancel = true; 
See Also