Thanks for using Syncfusion controls.
Query 1 -“My TreeView is linked with a database by a SqlDataSourceControl. Why the TreeView is cleared at each PostBack? And if set "EnabledPersistence" at True, data are incorrect!! it's very strange,”
We unable to reproduce the reported issue, so please share the issue reproducing sample or modify the attached sample and share the same with us with detailed steps with us.
Query 2 -“ I have checkboxes in my TreeView. How get the ID list of nodes which are checked??”
Yes, we can get the selected items text while check the node in ‘OnNodeChecked’ server side events. Please refer the below code snippet:
Dim CheckedNodes As ArrayList = TryCast(e.Arguments("currentCheckedNodes"), ArrayList)
lblChecked.Text = "checked Node List =>"
For Each sample As String In CheckedNodes
lblChecked.Text = lblChecked.Text + sample & Convert.ToString("--")
Unfortunately we unable to get the id in ‘onNodeChecked’ event, in case if you want to collect the id of checked nodes, please report it as feature using Direct Track account.
We prepared the sample solution with reported scenario and attached in a bellow link:
Please let me know if you have any concerns.