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TreeView Class

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

For a list of all members of this type, see TreeView Members.

System.Object
   System.MarshalByRefObject
      System.ComponentModel.Component
         System.Windows.Forms.Control
            System.Windows.Forms.TreeView

[Visual Basic]
Public Class TreeView
   Inherits Control
[C#]
public class TreeView : Control
[C++]
public __gc class TreeView : public Control
[JScript]
public class TreeView extends Control

Thread Safety

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

Remarks

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 object to the ImageList property, and referencing the index value of an Image in the ImageList to assign that Image. Set the ImageIndex property to the index value of the Image that you want to display when a tree node is not selected. Likewise, 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. Each tree node 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.

Note   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 object 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.

Note   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.

Example

[Visual Basic, C#, C++] The following 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 assumes you have a Customer object that can hold a collection of Order objects. It also assumes 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.

[Visual Basic] 
' 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

[C#] 
// Create a new ArrayList to hold the Customer objects.
private ArrayList customerArray = new ArrayList(); 

private void FillMyTreeView()
{
   // Add customers to the ArrayList of Customer objects.
   for(int x=0; x<1000; x++)
   {
      customerArray.Add(new Customer("Customer" + x.ToString()));
   }

   // Add orders to each Customer object in the ArrayList.
   foreach(Customer customer1 in customerArray)
   {
      for(int y=0; y<15; y++)
      {
         customer1.CustomerOrders.Add(new Order("Order" + y.ToString()));    
      }
   }

   // 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.
   foreach(Customer customer2 in customerArray)
   {
      treeView1.Nodes.Add(new TreeNode(customer2.CustomerName));
          
      // Add a child treenode for each Order object in the current Customer object.
      foreach(Order order1 in customer2.CustomerOrders)
      {
         treeView1.Nodes[customerArray.IndexOf(customer2)].Nodes.Add(
           new TreeNode(customer2.CustomerName + "." + order1.OrderID));
      }
   }

   // Reset the cursor to the default for all controls.
   Cursor.Current = Cursors.Default;

   // Begin repainting the TreeView.
   treeView1.EndUpdate();
}

[C++] 
void FillMyTreeView() {
    // Add customers to the ArrayList of Customer objects.
    for (int x=0; x<1000; x++) {
        customerArray->Add(new Customer(String::Concat(S"Customer ", __box(x))));
    }

    // Add orders to each Customer object in the ArrayList.
    IEnumerator* myEnum = customerArray->GetEnumerator();
    while (myEnum->MoveNext()) {
        Customer* customer1 = __try_cast<Customer*>(myEnum->Current);

        for (int y=0; y<15; y++) {
            customer1->CustomerOrders->Add(new Order(String::Concat(S"Order ", __box(y))));
        }
    }

    // Display a wait cursor while the TreeNodes are being created.
    Cursor::Current = new System::Windows::Forms::Cursor(S"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.
    while (myEnum->MoveNext()) {
        Customer* customer2 = __try_cast<Customer*>(myEnum->Current);

        treeView1->Nodes->Add(new TreeNode(customer2->CustomerName));

        // Add a child treenode for each Order object in the current Customer object.
        IEnumerator* myEnum = customer2->CustomerOrders->GetEnumerator();
        while (myEnum->MoveNext()) {
            Order* order1 = __try_cast<Order*>(myEnum->Current);

            treeView1->Nodes->Item[customerArray->IndexOf(customer2)]->Nodes->Add(
                new TreeNode(String::Concat(customer2->CustomerName, S".", order1->OrderID)));
        }
    }

    // Reset the cursor to the default for all controls.
    Cursor::Current = Cursors::Default;

    // Begin repainting the TreeView.
    treeView1->EndUpdate();
}

[JScript] No example is available for JScript. To view a Visual Basic, C#, or C++ example, click the Language Filter button Language Filter in the upper-left corner of the page.

Requirements

Namespace: System.Windows.Forms

Platforms: Windows 98, Windows NT 4.0, Windows Millennium Edition, Windows 2000, Windows XP Home Edition, Windows XP Professional, Windows Server 2003 family, .NET Compact Framework

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

See Also

TreeView Members | System.Windows.Forms Namespace | TreeNode

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