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TreeView.OnTreeNodePopulate Method

Raises the TreeNodePopulate event of the TreeView control.

Namespace:  System.Web.UI.WebControls
Assembly:  System.Web (in System.Web.dll)

protected virtual void OnTreeNodePopulate(
	TreeNodeEventArgs e


Type: System.Web.UI.WebControls.TreeNodeEventArgs
A TreeNodeEventArgs that contains event data.

Sometimes, it is not practical to statically predefine the tree structure due to data size or custom content that depends on user input. Because of this, the TreeView control supports dynamic node population. When the PopulateOnDemand property for a node is set to true, that node gets populated at run time when the node is expanded.

To populate a node dynamically, first set the PopulateOnDemand property for the node to true. Next, define an event-handling method for the TreeNodePopulate event that programmatically populates the node. A typical event-handling method retrieves node data from a data source, places the data into a node structure, and then adds the node structure to the ChildNodes collection of the node being populated. A node structure is created by adding TreeNode objects to the ChildNodes collection of a parent node.


When the PopulateOnDemand property for a node is set to true, the node must be populated dynamically. You cannot declaratively nest another node below it; otherwise, an error will occur on the page.

Supported browsers (Microsoft Internet Explorer 4.0-compatible browsers and later) can also take advantage of client-side node population. When enabled, this allows the TreeView control to populate a node on the client dynamically when that node is expanded, which prevents the need to post back to the server. For more information on client-side node population, see PopulateNodesFromClient.

Raising an event invokes the event handler through a delegate. For more information, see Consuming Events.

The OnTreeNodePopulate method also allows derived classes to handle the event without attaching a delegate. This is the preferred technique for handling the event in a derived class.

Notes to Inheritors

When overriding the OnTreeNodePopulate method in a derived class, be sure to call the OnTreeNodePopulate method for the base class so that registered delegates receive the event.

.NET Framework

Supported in: 4, 3.5, 3.0, 2.0

Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows XP SP2 x64 Edition, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.