ASP.NET: How to Create an Expandable Empty TreeNode

Question

I need to populate the TreeNode.ChildNodes on the event of TreeView.TreeNodeExpanded. The problem is the node is empty before the event gets fired

Answer 1

Three steps to do the trick:

1 - Set the TreeView.ExpandDepth to 0. This eliminates the expansion of the added TreeNode objects in the TreeView and shows the expansion symbol [+] next to each TreeNode that has the TreeNode.PopulateOnDemand property set to true.

2- Set the TreeNode.PopulateOnDemand to True for each branch TreeNode. When the TreeNode.ChildNodes collection is empty, the expansion symbol [+] will be showed only next to TreeNode objects that has TreeNode.PopulateOnDemand property set to true.

3- Handle the TreeView.TreeNodePopulate event to poulate branch nodes on expansion. This event will be fired when a TreeNode - with the TreeNode.PopulateOnDemand set to true - has been expanded right before the TreeView.TreeNodeExpanded event gets fired.

Answer 2

I suggest editing the template of the node. Have a look at An ASP.NET AJAX TreeView control with templates.

Answer 3

Not sure and do not have time to try but I guess what you are after is the TreeNode.PopulateOnDemand property and TreeView.TreeNodePopulate event.