TreeViewCancelEventHandler Delegato

Definizione

Rappresenta il metodo che gestirà l'evento BeforeCheck, BeforeCollapse, BeforeExpand o BeforeSelect di un controllo TreeView.Represents the method that will handle the BeforeCheck, BeforeCollapse, BeforeExpand, or BeforeSelect event of a TreeView.

public delegate void TreeViewCancelEventHandler(System::Object ^ sender, TreeViewCancelEventArgs ^ e);
public delegate void TreeViewCancelEventHandler(object sender, TreeViewCancelEventArgs e);
type TreeViewCancelEventHandler = delegate of obj * TreeViewCancelEventArgs -> unit
Public Delegate Sub TreeViewCancelEventHandler(sender As Object, e As TreeViewCancelEventArgs)

Parametri

sender
Object

Origine dell'evento.The source of the event.

e
TreeViewCancelEventArgs

Oggetto TreeViewCancelEventArgs che contiene i dati dell'evento.A TreeViewCancelEventArgs that contains the event data.

Esempio

Nell'esempio seguente viene illustrato come modificare lo stato di compressione di un oggetto in TreeView modo che tutti i nodi controllati siano visibili.The following example demonstrates how to change the collapse state of a TreeView so that all the checked nodes are visible. Prima di tutto, tutti i nodi vengono compressi e viene aggiunto un gestore all' TreeView.BeforeExpand evento.First, all the nodes are collapsed, and a handler is added to the TreeView.BeforeExpand event. Quindi, tutti i nodi vengono espansi.Next, all the nodes are expanded. Il TreeView.BeforeExpand gestore eventi determina se un determinato nodo dispone di nodi figlio che sono controllati.The TreeView.BeforeExpand event handler determines whether a given node has child nodes that are checked. Se un nodo non dispone di elementi figlio controllati, l'espansione viene annullata per tale nodo.If a node does not have checked children, the expansion is canceled for that node. Per consentire l'espansione normale del nodo quando si fa clic sul segno più accanto a un nodo, il TreeView.BeforeExpand gestore eventi viene quindi rimosso.In order to allow normal node expansion when the plus sign next to a node is clicked, the TreeView.BeforeExpand event handler is then removed.

Questo comportamento può essere implementato anche gestendo l' TreeView.BeforeCollapse evento, come illustrato nell'esempio relativo a tale argomento.This behavior can also be implemented by handling the TreeView.BeforeCollapse event, as illustrated in the example for that topic.

#using <System.dll>
#using <System.Windows.Forms.dll>
#using <System.Drawing.dll>

using namespace System;
using namespace System::Drawing;
using namespace System::Windows::Forms;
public ref class Form1: public Form
{
private:
   TreeView^ treeView1;
   Button^ showCheckedNodesButton;
   TreeViewCancelEventHandler^ checkForCheckedChildren;

public:
   Form1()
   {
      treeView1 = gcnew TreeView;
      showCheckedNodesButton = gcnew Button;
      checkForCheckedChildren = gcnew TreeViewCancelEventHandler( this, &Form1::CheckForCheckedChildrenHandler );
      this->SuspendLayout();
      
      // Initialize treeView1.
      treeView1->Location = Point(0,25);
      treeView1->Size = System::Drawing::Size( 292, 248 );
      treeView1->Anchor = static_cast<AnchorStyles>(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 = System::Drawing::Size( 144, 24 );
      showCheckedNodesButton->Text = "Show Checked Nodes";
      showCheckedNodesButton->Click += gcnew EventHandler( this, &Form1::showCheckedNodesButton_Click );
      
      // Initialize the form.
      this->ClientSize = System::Drawing::Size( 292, 273 );
      array<Control^>^temp0 = {showCheckedNodesButton,treeView1};
      this->Controls->AddRange( temp0 );
      this->ResumeLayout( false );
   }

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.
   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.
   bool HasCheckedChildNodes( TreeNode^ node )
   {
      if ( node->Nodes->Count == 0 )
            return false;

      System::Collections::IEnumerator^ myEnum = node->Nodes->GetEnumerator();
      while ( myEnum->MoveNext() )
      {
         TreeNode^ childNode = safe_cast<TreeNode^>(myEnum->Current);
         if ( childNode->Checked )
                  return true;

         // Recursively check the children of the current child node.
         if ( HasCheckedChildNodes( childNode ) )
                  return true;
      }

      return false;
   }
};

int main()
{
   Application::Run( gcnew Form1 );
}
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;
    }
}
Imports System.Drawing
Imports System.Windows.Forms

Public Class Form1
    Inherits Form
    Private treeView1 As TreeView
    Private showCheckedNodesButton As Button

    Public Sub New()
        treeView1 = New TreeView
        showCheckedNodesButton = New Button

        Me.SuspendLayout()

        ' Initialize treeView1.
        treeView1.Location = New Point(0, 25)
        treeView1.Size = New Size(292, 248)
        treeView1.Anchor = AnchorStyles.Top Or AnchorStyles.Left Or AnchorStyles.Bottom Or AnchorStyles.Right
        treeView1.CheckBoxes = True

        ' Add nodes to treeView1.
        Dim node As TreeNode
        Dim x As Integer
        For x = 0 To 3
            ' Add a root node.
            node = treeView1.Nodes.Add(String.Format("Node{0}", x * 4))
            Dim y As Integer
            For y = 1 To 4
                ' Add a node as a child of the previously added node.
                node = node.Nodes.Add(String.Format("Node{0}", x * 4 + y))
            Next y
        Next x

        ' 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"
        AddHandler showCheckedNodesButton.Click, AddressOf showCheckedNodesButton_Click

        ' Initialize the form.
        Me.ClientSize = New Size(292, 273)
        Me.Controls.AddRange(New Control() {showCheckedNodesButton, treeView1})

        Me.ResumeLayout(False)
    End Sub

    <STAThreadAttribute()> _
    Shared Sub Main()
        Application.Run(New Form1)
    End Sub

    Private Sub showCheckedNodesButton_Click(ByVal sender As Object, ByVal e As EventArgs)
        ' 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.
        AddHandler treeView1.BeforeExpand, AddressOf 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.
        RemoveHandler treeView1.BeforeExpand, AddressOf CheckForCheckedChildren

        ' Enable redrawing of treeView1.
        treeView1.EndUpdate()
    End Sub

    ' Prevent expansion of a node that does not have any checked child nodes.
    Private Sub CheckForCheckedChildren(ByVal sender As Object, ByVal e As TreeViewCancelEventArgs)
        If Not HasCheckedChildNodes(e.Node) Then
            e.Cancel = True
        End If
    End Sub

    ' Returns a value indicating whether the specified 
    ' TreeNode has checked child nodes.
    Private Function HasCheckedChildNodes(ByVal node As TreeNode) As Boolean
        If node.Nodes.Count = 0 Then
            Return False
        End If
        Dim childNode As TreeNode
        For Each childNode In node.Nodes
            If childNode.Checked Then
                Return True
            End If
            ' Recursively check the children of the current child node.
            If HasCheckedChildNodes(childNode) Then
                Return True
            End If
        Next childNode
        Return False
    End Function 'HasCheckedChildNodes

End Class

Commenti

Quando si crea un delegato TreeViewCancelEventArgs, si identifica il metodo che gestirà l'evento.When you create a TreeViewCancelEventArgs delegate, you identify the method that will handle the event. Per associare l'evento al gestore eventi in uso, aggiungere all'evento un'istanza del delegato.To associate the event with your event handler, add an instance of the delegate to the event. Il gestore eventi viene chiamato ogni volta che si verifica l'evento, a meno che non venga rimosso il delegato.The event handler is called whenever the event occurs, unless you remove the delegate. Per ulteriori informazioni sui delegati del gestore eventi, vedere gestione e generazione di eventi.For more information about event handler delegates, see Handling and Raising Events.

Metodi di estensione

GetMethodInfo(Delegate)

Ottiene un oggetto che rappresenta il metodo rappresentato dal delegato specificato.Gets an object that represents the method represented by the specified delegate.

Si applica a

Vedi anche