How to obtain the node value after onselectednodechanged is dynamically loaded in Treeview with ontreenodepopulate

In section 2.0, the Treeview uses ontreenodepopulate to dynamically load data. The data can be loaded. But how can I obtain a specific node VALUE OF THE Treeview?
In addition, as long as the page is PostBack, no data is loaded by the Treeview.
How can I solve these problems? In addition, as long as the page is PostBack, no data is loaded by the Treeview.
Your binding has been put in the wrong place. Do not place it in if (! Ispostback) The Treeview in section 2.0 uses ontreenodepopulate to dynamically load data. The data can be loaded, but how can we get the specific node value of the Treeview?
----------------
Use treeview1.nodes [0]. Value to obtain the value of the corresponding node. If it is a subnode, use:
This. treeview1.nodes [0]. childnodes [I]. Value
This. treeview1.nodes [0]. childnodes [I]. childnodes [I]. Value