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.v24.2.dll

NuGet Package: DevExpress.Blazor

Declaration

[Parameter]
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.

Remarks

The following code snippet prohibits root-level nodes from collapsing.

<DxTreeView BeforeCollapse="@BeforeCollapse">
    ...
</DxTreeView>

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