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TreeView Class

Displays a hierarchical collection of labeled items, each represented by a TreeNode.

Namespace:  System.Windows.Forms
Assembly:  System.Windows.Forms (in System.Windows.Forms.dll)

'Declaration
<ComVisibleAttribute(True)> _
<DockingAttribute(DockingBehavior.Ask)> _
<ClassInterfaceAttribute(ClassInterfaceType.AutoDispatch)> _
Public Class TreeView _
	Inherits Control
'Usage
Dim instance As TreeView

The Nodes collection holds all the TreeNode objects that are assigned to the TreeView 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:

  • Set the ImageIndex property to the index value of the Image that you want to display when a tree node is not selected.

  • Set the SelectedImageIndex property to the index value of the Image that you want to display when a tree node is selected.

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.

Tree nodes can optionally display check boxes. To display the check boxes, set the CheckBoxes property of the TreeView to true. The Checked property is set to true for tree nodes that are in a checked state.

NoteNote:

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 TreeView 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 TreeView 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 TreeView control. To do this, set the DrawMode property to a value other than TreeViewDrawMode.Normal and handle the DrawNode event.

NoteNote:

When setting the CheckBoxes, Scrollable, ImageIndex, and SelectedImageIndex properties at run time, the TreeView handle is recreated (see Control.RecreateHandle) to update the control's appearance. This causes all tree nodes to be collapsed, with the exception of the selected TreeNode.

The following code example demonstrates the use of the TreeView 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 TreeView 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 TreeView is suppressed by using the BeginUpdate and EndUpdate methods, and a wait Cursor is displayed while the TreeView 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 TreeView 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

Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.

Windows 7, Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98, Windows CE, Windows Mobile for Smartphone, Windows Mobile for Pocket PC

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.

.NET Framework

Supported in: 3.5, 3.0, 2.0, 1.1, 1.0

.NET Compact Framework

Supported in: 3.5, 2.0, 1.0

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