Hi thomas kuang,
Thank you for the clarification. In order to display the tooltip only when the RadTreeViewItem is cropped you can implement the following:
(parentTreeViewItem.DesiredSize.Width == parentTreeViewItem.ActualWidth)
parentTreeViewItem.ToolTip = ((parentTreeViewItem.Header
We modified the project to implement this approach. Take a look at it and let me know if it works for you.
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