TreeView.BeforeExpand Event

 

Occurs before the tree node is expanded.

Namespace:   System.Windows.Forms
Assembly:  System.Windows.Forms (in System.Windows.Forms.dll)

member BeforeExpand : IEvent<TreeViewCancelEventHandler,
    TreeViewCancelEventArgs>

For more information about how to handle events, see Handling and Raising Events.

The following code example demonstrates how to change the collapse state of a TreeView so that all the checked nodes are visible. First, all the nodes are collapsed, and a handler is added for the BeforeExpand event. Next, all the nodes are expanded. The BeforeExpand event handler determines whether a given node has child nodes that are checked. If a node does not have checked children, the expansion is canceled for that node. In order to allow standard node expansion when the plus sign next to a node is clicked, the BeforeExpand event handler is then removed.

This behavior can also be implemented by handling the BeforeCollapse event, as illustrated in the example for that topic.

For the complete example, see the CheckBoxes reference topic.

No code example is currently available or this language may not be supported.

.NET Framework
Available since 1.1
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