Persisting the Expanded State
The TreeView enables you to define and persist the expanded state of its nodes when the component is re-rendered.
Basics
The TreeView exposes the following options to control the expand state:
isExpanded(function)—Determines if a given node is expanded.collapse(event)—Fired when a given node is about to be collapsed.expand(event)—Fired when a given node is about to be expanded.
The following example demonstrates how to manually control the expand state of TreeView nodes by implementing the isExpanded function and handling the expand and collapse events.
Built-in Directives
To persist the expanded state of the TreeView, either:
Using the Built-In Directive
By default, the built-in ExpandDirective persists the expanded items based on their hierarchical index.
The TreeView renders the expand icons only after the
childrenandhasChildrenfunctions are defined.
The following example demonstrates how to use the built-in ExpandDirective to automatically persist the expanded state of TreeView nodes by their hierarchical index.
Setting an Item Field
You can also persist the expanded state of the TreeView by item field—for example, the id field.
Expand Disabled Nodes
The component can be configured to allow exapnding disabled nodes by setting the expandDisabledNodes option to true.