TreeList.BeforeCollapse Event

The event handler receives an argument of type BeforeCollapseEventArgs containing data related to this event.

By default, the following actions result in collapsing a parent node:

• An end-user user has clicked the node's collapse button, double-clicked its corresponding indicator cell or pressed the PLUS or CTRL + LEFT ARROW keys when the node is focused.
• The node has been collapsed in code via the TreeListNode.Expanded property, the CollapseToLevel or CollapseAll method.

Each time a node is about to be collapsed, the BeforeCollapse event fires. Write a handler for this event to specify whether the node is allowed to be collapsed. You must set the event's BeforeCollapseEventArgs.CanCollapse parameter to false to prohibit this action.

You can use the event for the following purposes:

• Prohibit the ability to collapse a specific node(s).
• Allow the ability to collapse nodes only when certain conditions are met.

If you want specific actions to be performed each time a node is collapsed, consider using the AfterCollapse event.

Example

using DevExpress.XtraTreeList;

private void treeList1_BeforeCollapse(object sender, BeforeCollapseEventArgs e) {
   if (e.Node.Level == 0) e.CanCollapse = false;
}

Imports DevExpress.XtraTreeList

Private Sub TreeList1_BeforeCollapse(ByVal sender As Object, _
ByVal e As BeforeCollapseEventArgs) Handles TreeList1.BeforeCollapse
   If e.Node.Level = 0 Then e.CanCollapse = False 
End Sub