The TreeNode Editor

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'Add Root' will add a root element (one with no parent e.g., World in the above window). 'Add Child' will add a child node to the selected element. The label of the nodes can be changed using the text box labeled 'Label'. A node can be deleted using the 'Delete' button.

Adding/Removing items at runtime

Items can be added to or removed from the tree view using the TreeNode editor at design time, but most of the time we need to add/remove items at runtime using our code. The TreeView class contains a property called 'Nodes' which provides access to the individual nodes of the control. The Add() method of the Nodes collection can be used to add a text item or a TreeNode object which itself may have child tree nodes. The following code adds a sample tree hierarchy on the form's Load event.

private void MyForm_Load(object sender, System.EventArgs e)

{

treeView1.Nodes.Clear();

treeView1.Nodes.Add("Programming Languages");

TreeNode node = new TreeNode("Object Oriented Programming Languages");

node.Nodes.Add("C++");

TreeNode subnode = node.Nodes.Add("Framework and runtime based languages");

subnode.Nodes.Add("Java");

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subnode.Nodes.Add("C#");

treeView1.Nodes[0].Nodes.Add(node);

}

First we have added a root node labeled 'Programming Languages'. We then created a new TreeNode and added sub nodes to it. Finally we added this node to the root node. When we execute the program, the following screen is produced.

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Tree View Events

Tree View has a number of important events, some of which are listed below.

The following event handler will show the label of the node in a Message box whenever it is selected.

private void treeView1_AfterSelect(object sender, System.Windows.Forms.TreeViewEventArgs e)

{

MessageBox.Show("'" + e.Node.Text + "' node selected", "Selected Node");

}

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