1. Here is a sample that shows how to add control on a page
var pagemanager = PageManager.GetManager();
var cntrl = pagemanager.CreateControl<PageControl>();
var page = pagemanager.GetPageNodes().First();
2. You can use attributes, value or text properties of the RadTreeNode to make the association with the content item.
Note that if you want persist the controls and the value you set for some properties, this will make database transactions and if there are many users on the website this will cause performance issues.
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