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TreeViewCancelEventHandler (Delegado)

Representa el método que controlará el evento BeforeCheck, BeforeCollapse, BeforeExpand o BeforeSelect de TreeView.

Espacio de nombres: System.Windows.Forms
Ensamblado: System.Windows.Forms (en system.windows.forms.dll)

public delegate void TreeViewCancelEventHandler (
	Object sender,
	TreeViewCancelEventArgs e
)
/** @delegate */
public delegate void TreeViewCancelEventHandler (
	Object sender, 
	TreeViewCancelEventArgs e
)
No aplicable.

Parámetros

sender

Origen del evento.

e

TreeViewCancelEventArgs que contiene los datos del evento.

Cuando se crea un delegado de TreeViewCancelEventArgs, se identifica el método que controlará el evento. Para asociar el evento con el controlador del evento, hay que agregar una instancia del delegado al evento. Siempre que se produce el evento, se llama al controlador del evento, a menos que se quite el delegado. Para obtener más información acerca de delegados del controlador de eventos, vea Eventos y delegados.

En el siguiente ejemplo se muestra cómo cambiar el estado de contracción de TreeView de modo que se vean todos los nodos activados. Primero, todos los nodos están contraídos y se agrega un controlador al evento TreeView.BeforeExpand. A continuación, se expanden todos los nodos. El controlador de eventos TreeView.BeforeExpand determina si un nodo dado tiene nodos secundarios que están activados. Si un nodo no tiene nodos secundarios activados, se cancela la expansión para dicho nodo. Para que un nodo normal se expanda cuando se hace clic en el signo más situado junto al nodo, se quita el controlador de eventos TreeView.BeforeExpand.

Este comportamiento se puede implementar también controlando el evento TreeView.BeforeCollapse, tal y como se muestra en el ejemplo correspondiente a dicho tema.

using System;
using System.Drawing;
using System.Windows.Forms;

public class Form1 : Form
{
    private TreeView treeView1;
    private Button showCheckedNodesButton;
    private TreeViewCancelEventHandler checkForCheckedChildren;

    public Form1()
    {
        treeView1 = new TreeView();
        showCheckedNodesButton = new Button();
        checkForCheckedChildren = 
            new TreeViewCancelEventHandler(CheckForCheckedChildrenHandler);

        this.SuspendLayout();

        // Initialize treeView1.
        treeView1.Location = new Point(0, 25);
        treeView1.Size = new Size(292, 248);
        treeView1.Anchor = AnchorStyles.Top | AnchorStyles.Left | 
            AnchorStyles.Bottom | AnchorStyles.Right;
        treeView1.CheckBoxes = true;

        // Add nodes to treeView1.
        TreeNode node;
        for (int x = 0; x < 3; ++x)
        {
            // Add a root node.
            node = treeView1.Nodes.Add(String.Format("Node{0}", x*4));
            for (int y = 1; y < 4; ++y)
            {
                // Add a node as a child of the previously added node.
                node = node.Nodes.Add(String.Format("Node{0}", x*4 + y));
            }
        }

        // Set the checked state of one of the nodes to
        // demonstrate the showCheckedNodesButton button behavior.
        treeView1.Nodes[1].Nodes[0].Nodes[0].Checked = true;

        // Initialize showCheckedNodesButton.
        showCheckedNodesButton.Size = new Size(144, 24);
        showCheckedNodesButton.Text = "Show Checked Nodes";
        showCheckedNodesButton.Click += 
            new EventHandler(showCheckedNodesButton_Click);

        // Initialize the form.
        this.ClientSize = new Size(292, 273);
        this.Controls.AddRange(new Control[] 
            { showCheckedNodesButton, treeView1 } );

        this.ResumeLayout(false);
    }

    [STAThreadAttribute()]
    static void Main() 
    {
        Application.Run(new Form1());
    }

    private void showCheckedNodesButton_Click(object sender, EventArgs e)
    {
        // Disable redrawing of treeView1 to prevent flickering 
        // while changes are made.
        treeView1.BeginUpdate();

        // Collapse all nodes of treeView1.
        treeView1.CollapseAll();

        // Add the checkForCheckedChildren event handler to the BeforeExpand event.
        treeView1.BeforeExpand += checkForCheckedChildren;

        // Expand all nodes of treeView1. Nodes without checked children are 
        // prevented from expanding by the checkForCheckedChildren event handler.
        treeView1.ExpandAll();

        // Remove the checkForCheckedChildren event handler from the BeforeExpand 
        // event so manual node expansion will work correctly.
        treeView1.BeforeExpand -= checkForCheckedChildren;

        // Enable redrawing of treeView1.
        treeView1.EndUpdate();
    }

    // Prevent expansion of a node that does not have any checked child nodes.
    private void CheckForCheckedChildrenHandler(object sender, 
        TreeViewCancelEventArgs e)
    {
        if (!HasCheckedChildNodes(e.Node)) e.Cancel = true;
    }

    // Returns a value indicating whether the specified 
    // TreeNode has checked child nodes.
    private bool HasCheckedChildNodes(TreeNode node)
    {
        if (node.Nodes.Count == 0) return false;
        foreach (TreeNode childNode in node.Nodes)
        {
            if (childNode.Checked) return true;
            // Recursively check the children of the current child node.
            if (HasCheckedChildNodes(childNode)) return true;
        }
        return false;
    }

}

import System.*;
import System.Drawing.*;
import System.Windows.Forms.*;

public class Form1 extends Form
{
    private TreeView treeView1;
    private Button showCheckedNodesButton;
    private TreeViewCancelEventHandler checkForCheckedChildren;

    public Form1()
    {
        treeView1 = new TreeView();
        showCheckedNodesButton = new Button();
        checkForCheckedChildren =
            new TreeViewCancelEventHandler(CheckForCheckedChildrenHandler);

        this.SuspendLayout();
        // Initialize treeView1.
        treeView1.set_Location(new Point(0, 25));
        treeView1.set_Size(new Size(292, 248));
        treeView1.set_Anchor(AnchorStyles.Top | AnchorStyles.Left
            | AnchorStyles.Bottom | AnchorStyles.Right);
        treeView1.set_CheckBoxes(true);
        // Add nodes to treeView1.
        TreeNode node;
        for (int x = 0; x < 3; ++x) {
            // Add a root node.
            node = treeView1.get_Nodes().Add(String.Format
                ("Node{0}", (Int32)(x * 4)));
            for (int y = 1; y < 4; ++y) {
                // Add a node as a child of the previously added node.
                node = node.get_Nodes().Add(String.Format
                    ("Node{0}", (Int32)(x * 4 + y)));
            }
        }
        // Set the checked state of one of the nodes to
        // demonstrate the showCheckedNodesButton button behavior.
        treeView1.get_Nodes().get_Item(1).get_Nodes().get_Item(0).
            get_Nodes().get_Item(0).set_Checked(true);
        // Initialize showCheckedNodesButton.
        showCheckedNodesButton.set_Size(new Size(144, 24));
        showCheckedNodesButton.set_Text("Show Checked Nodes");
        showCheckedNodesButton.add_Click(
            new EventHandler(showCheckedNodesButton_Click));
        // Initialize the form.
        this.set_ClientSize(new Size(292, 273));
        this.get_Controls().AddRange(new Control[]
            { showCheckedNodesButton, treeView1 });

        this.ResumeLayout(false);
    } //Form1

    public static void main(String[] args)
    {
        Application.Run(new Form1());
    } //main

    private void showCheckedNodesButton_Click(Object sender, EventArgs e)
    {
        // Disable redrawing of treeView1 to prevent flickering 
        // while changes are made.
        treeView1.BeginUpdate();
        // Collapse all nodes of treeView1.
        treeView1.CollapseAll();
        // Add the checkForCheckedChildren event handler to the
        // BeforeExpand event.
        treeView1.add_BeforeExpand(checkForCheckedChildren);
        // Expand all nodes of treeView1. Nodes without checked children are 
        // prevented from expanding by the checkForCheckedChildren event handler.
        treeView1.ExpandAll();
        // Remove the checkForCheckedChildren event handler from
        // the BeforeExpand 
        // event so manual node expansion will work correctly.
        treeView1.remove_BeforeExpand(checkForCheckedChildren);
        // Enable redrawing of treeView1.
        treeView1.EndUpdate();
    } //showCheckedNodesButton_Click

    // Prevent expansion of a node that does not have any checked child nodes.
    private void CheckForCheckedChildrenHandler(Object sender,
        TreeViewCancelEventArgs e)
    {
        if (!(HasCheckedChildNodes(e.get_Node()))) {
            e.set_Cancel(true);
        }
    } //CheckForCheckedChildrenHandler

    // Returns a value indicating whether the specified 
    // TreeNode has checked child nodes.
    private boolean HasCheckedChildNodes(TreeNode node)
    {
        if (node.get_Nodes().get_Count() == 0) {
            return false;
        }
        for (int iCtr = 0; iCtr < node.get_Nodes().get_Count(); iCtr++) {
            TreeNode childNode = node.get_Nodes().get_Item(iCtr);
            if (childNode.get_Checked()) {
                return true;
            }
            // Recursively check the children of the current child node.
            if (HasCheckedChildNodes(childNode)) {
                return true;
            }
        }
        return false;
    } //HasCheckedChildNodes
} //Form1

Windows 98, Windows 2000 Service Pack 4, Windows CE, Windows Millennium, Windows Mobile para Pocket PC, Windows Mobile para Smartphone, Windows Server 2003, Windows XP Media Center, Windows XP Professional x64, Windows XP SP2, Windows XP Starter

Microsoft .NET Framework 3.0 es compatible con Windows Vista, Microsoft Windows XP SP2 y Windows Server 2003 SP1.

.NET Framework

Compatible con: 3.0, 2.0, 1.1, 1.0

.NET Compact Framework

Compatible con: 2.0, 1.0
Mostrar:
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