TreeView Class

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.

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 that 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.

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, except for the selected TreeNode.

The following code example demonstrates the use of the TreeView control.

// Populates a TreeView control with example nodes. 
private void 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();
}

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 that is named MyWait.cur in the application directory and that you have created an instance of a TreeView control on a Form.

// The basic Customer class.
public class Customer : System.Object
{
   private string custName = "";
   protected ArrayList custOrders = new ArrayList();

   public Customer(string customername)
   {
      this.custName = customername;
   }

   public string CustomerName
   {      
      get{return this.custName;}
      set{this.custName = value;}
   }

   public ArrayList CustomerOrders 
   {
      get{return this.custOrders;}
   }

} // End Customer class 


// The basic customer Order class.
public class Order : System.Object
{
   private string ordID = "";

   public Order(string orderid)
   {
      this.ordID = orderid;
   }

   public string OrderID
   {      
      get{return this.ordID;}
      set{this.ordID = value;}
   }

} // End Order class

// 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();
}

.NET Framework

.NET Framework Client Profile

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

Reference