Virtual Mode

In addition to bound and unbound modes, the DevExpress ASP.NET Tree List (ASPxTreeList) can operate in Virtual Mode. This mode is useful when binding to large data sets.

In virtual mode, a tree is created on demand. In this case, child nodes are created and initialized when the parent node is expanded.

The ASPxTreeList fires the following two events, which you should process in code.

• VirtualModeCreateChildren;
• VirtualModeNodeCreating.

Within the VirtualModeCreateChildren event handler, create a list of business objects that correspond to the child nodes owned by the processed node.

The VirtualModeNodeCreating event is raised for each node object created within the VirtualModeCreateChildren event handler. This event enables you to initialize the corresponding node in a tree. Here, you should specify the node's key value and cell values. If you are certain that the processed node has no child nodes, set the event parameter's e.IsLeaf property to true.

In the demo, the ASPxTreeList control uses this data binding method to display the file/folder tree of this demo web site.