Displays a hierarchical collection of labeled items, each represented by a TreeNode.
Assembly: System.Windows.Forms (in System.Windows.Forms.dll)
The Nodes collection holds all the TreeNode objects that are assigned to the control. The tree nodes in this collection are referred to as the root tree nodes. Any tree node that is subsequently added to a root tree node is referred to as a child node. Because each TreeNode can contain a collection of other TreeNode objects, you might find it difficult to determine your location in the tree structure when you iterate through the collection. You can parse the TreeNode.FullPath string by using the PathSeparator string value to determine where a TreeNode label begins and ends.
You can display images next to the tree nodes by assigning an ImageList to the ImageList property and referencing the index value of an Image in the ImageList to assign that Image. Use the following properties to assign images:
The images referenced by the ImageIndex and SelectedImageIndex property values are the default images displayed by all the tree nodes that are assigned to the Nodes collection. Individual tree nodes can override the default images by setting the TreeNode.ImageIndex and TreeNode.SelectedImageIndex properties.
Tree nodes can be expanded to display the next level of child tree nodes. The user can expand the TreeNode by clicking the plus-sign (+) button, if one is displayed next to the TreeNode, or you can expand the TreeNode by calling the TreeNode.Expand method. To expand all the child tree node levels in the Nodes collection, call the ExpandAll method. You can collapse the child TreeNode level by calling the TreeNode.Collapse method, or the user can press the minus-sign (-) button, if one is displayed next to the TreeNode. You can also call the TreeNode.Toggle method to alternate between the expanded and collapsed states.
Setting the TreeNode.Checked property from within the BeforeCheck or AfterCheck event causes the event to be raised multiple times and can result in unexpected behavior. For example, you might set the Checked property in the event handler when you are recursively updating the child nodes, so the user does not have to expand and check each one individually. To prevent the event from being raised multiple times, add logic to your event handler that only executes your recursive code if the Action property of the TreeViewEventArgs is not set to TreeViewAction.Unknown. For an example of how to do this, see the Example section of the AfterCheck or BeforeCheck events.
You can change the appearance of the control by setting some of its display and style properties. Setting ShowPlusMinus to true displays a plus-sign or minus-sign button next to each TreeNode that can be expanded or collapsed, respectively. Setting the ShowRootLines property to true causes the to display lines that join all the root tree nodes together. You can display lines that connect child tree nodes to their root node by setting the ShowLines property to true. Setting the HotTracking property to true changes the appearance of the tree node labels as the mouse pointer passes over them. When hot-tracked, the tree node labels take on the appearance of a hyperlink. You can also completely customize the appearance of the control. To do this, set the DrawMode property to a value other than TreeViewDrawMode.Normal and handle the DrawNode event.
The following code example demonstrates the use of the control.
' Populates a TreeView control with example nodes. Private Sub InitializeTreeView() treeView1.BeginUpdate() treeView1.Nodes.Add("Parent") treeView1.Nodes(0).Nodes.Add("Child 1") treeView1.Nodes(0).Nodes.Add("Child 2") treeView1.Nodes(0).Nodes(1).Nodes.Add("Grandchild") treeView1.Nodes(0).Nodes(1).Nodes(0).Nodes.Add("Great Grandchild") treeView1.EndUpdate() End Sub
The following, more complex code example displays customer information in a control. The root tree nodes display customer names, and the child tree nodes display the order numbers assigned to each customer. In this example, 1,000 customers are displayed with 15 orders each. The repainting of the is suppressed by using the BeginUpdate and EndUpdate methods, and a wait Cursor is displayed while the creates and paints the TreeNode objects. This example requires that you have a Customer object that can hold a collection of Order objects. It also requires that you have a cursor file named MyWait.cur in the application directory and that you have created an instance of a control on a Form.
Public Class Customer Inherits [Object] Private custName As String = "" Friend custOrders As New ArrayList() Public Sub New(ByVal customername As String) Me.custName = customername End Sub Public Property CustomerName() As String Get Return Me.custName End Get Set(ByVal Value As String) Me.custName = Value End Set End Property Public ReadOnly Property CustomerOrders() As ArrayList Get Return Me.custOrders End Get End Property End Class 'End Customer class Public Class Order Inherits [Object] Private ordID As String Public Sub New(ByVal orderid As String) Me.ordID = orderid End Sub 'New Public Property OrderID() As String Get Return Me.ordID End Get Set(ByVal Value As String) Me.ordID = Value End Set End Property End Class ' End Order class ' Create a new ArrayList to hold the Customer objects. Private customerArray As New ArrayList() Private Sub FillMyTreeView() ' Add customers to the ArrayList of Customer objects. Dim x As Integer For x = 0 To 999 customerArray.Add(New Customer("Customer" + x.ToString())) Next x ' Add orders to each Customer object in the ArrayList. Dim customer1 As Customer For Each customer1 In customerArray Dim y As Integer For y = 0 To 14 customer1.CustomerOrders.Add(New Order("Order" + y.ToString())) Next y Next customer1 ' Display a wait cursor while the TreeNodes are being created. Cursor.Current = New Cursor("MyWait.cur") ' Suppress repainting the TreeView until all the objects have been created. treeView1.BeginUpdate() ' Clear the TreeView each time the method is called. treeView1.Nodes.Clear() ' Add a root TreeNode for each Customer object in the ArrayList. Dim customer2 As Customer For Each customer2 In customerArray treeView1.Nodes.Add(New TreeNode(customer2.CustomerName)) ' Add a child TreeNode for each Order object in the current Customer object. Dim order1 As Order For Each order1 In customer2.CustomerOrders treeView1.Nodes(customerArray.IndexOf(customer2)).Nodes.Add( _ New TreeNode(customer2.CustomerName + "." + order1.OrderID)) Next order1 Next customer2 ' Reset the cursor to the default for all controls. Cursor.Current = System.Windows.Forms.Cursors.Default ' Begin repainting the TreeView. treeView1.EndUpdate() End Sub 'FillMyTreeView
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The .NET Framework and .NET Compact Framework do not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.