TreeView-Konstruktor

Artikel
08/20/2007

Initialisiert eine neue Instanz der TreeView-Klasse.

Namespace: System.Windows.Forms
Assembly: System.Windows.Forms (in system.windows.forms.dll)

Syntax

'Declaration
Public Sub New
'Usage
Dim instance As New TreeView

public TreeView ()

public:
TreeView ()

public TreeView ()

public function TreeView ()

Beispiel

Im folgenden Codebeispiel wird das Ändern des Zustands einer TreeView veranschaulicht, um alle aktivierten Knoten anzuzeigen. Zu Beginn sind alle Knoten erweitert, und für das BeforeCollapse-Ereignis wird ein Handler hinzugefügt. Anschließend werden alle Knoten reduziert. Der BeforeCollapse-Ereignishandler bestimmt, ob ein bestimmter Knoten über aktivierte untergeordnete Knoten verfügt. Wenn ein Knoten über aktivierte untergeordnete Knoten verfügt, wird die Reduzierung an dem Knoten beendet. Damit Knoten wieder standardmäßig über Klicken auf das Minuszeichen neben dem Knoten reduziert werden können, wird der BeforeCollapse-Ereignishandler anschließend entfernt.

Dieses Verhalten können Sie auch durch Behandeln des BeforeExpand-Ereignisses implementieren. Das entsprechende Vorgehen wird im Beispiel zu dem Thema veranschaulicht.

Imports System
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 'New
    
    <STAThreadAttribute()> _
    Shared Sub Main()
        Application.Run(New Form1())
    End Sub 'Main
    
    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.ExpandAll()

        ' Add the CheckForCheckedChildren event handler to the BeforeExpand event.
        AddHandler treeView1.BeforeCollapse, AddressOf CheckForCheckedChildren

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

        ' Remove the checkForCheckedChildren event handler from the BeforeExpand 
        ' event so manual node expansion will work correctly.
        RemoveHandler treeView1.BeforeCollapse, AddressOf CheckForCheckedChildren
        ' Enable redrawing of treeView1.
        treeView1.EndUpdate()
    End Sub 'showCheckedNodesButton_Click


    ' Prevent collapse of a node that has checked child nodes.
    Private Sub CheckForCheckedChildren(ByVal sender As Object, ByVal e As TreeViewCancelEventArgs)
        If HasCheckedChildNodes(e.Node) Then
            e.Cancel = True
        End If
    End Sub 'CheckForCheckedChildren

    ' 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 '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.ExpandAll();

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

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

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

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

    // Prevent collapse of a node that has 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;
    }

}

#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^>^temp1 = {showCheckedNodesButton,treeView1};
      this->Controls->AddRange( temp1 );
      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->ExpandAll();
      
      // Add the checkForCheckedChildren event handler to the BeforeExpand event.
      treeView1->BeforeCollapse += checkForCheckedChildren;
      
      // Expand all nodes of treeView1. Nodes without checked children are 
      // prevented from expanding by the checkForCheckedChildren event handler.
      treeView1->CollapseAll();
      
      // Remove the checkForCheckedChildren event handler from the BeforeExpand 
      // event so manual node expansion will work correctly.
      treeView1->BeforeCollapse -= checkForCheckedChildren;
      
      // Enable redrawing of treeView1.
      treeView1->EndUpdate();
   }

   // Prevent collapse of a node that has 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 );
}

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.ExpandAll();
        // Add the checkForCheckedChildren event handler to the 
        // BeforeExpand event.
        treeView1.add_BeforeCollapse(checkForCheckedChildren);
        // Expand all nodes of treeView1. Nodes without checked children are 
        // prevented from expanding by the checkForCheckedChildren event handler.
        treeView1.CollapseAll();
        // Remove the checkForCheckedChildren event handler from the
        // BeforeExpand event so manual node expansion will work correctly.
        treeView1.remove_BeforeCollapse(checkForCheckedChildren);
        // Enable redrawing of treeView1.
        treeView1.EndUpdate();
    } //showCheckedNodesButton_Click

    // Prevent collapse of a node that has 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

Plattformen

Windows 98, Windows 2000 SP4, Windows CE, Windows Millennium Edition, Windows Mobile für Pocket PC, Windows Mobile für Smartphone, Windows Server 2003, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP SP2, Windows XP Starter Edition

.NET Framework unterstützt nicht alle Versionen sämtlicher Plattformen. Eine Liste der unterstützten Versionen finden Sie unter Systemanforderungen.

Freigeben über

TreeView-Konstruktor

Syntax

Beispiel

Plattformen

Versionsinformationen

.NET Framework

.NET Compact Framework

Siehe auch

Referenz

Zusätzliche Ressourcen