TreeViewCancelEventHandler-Delegat
Stellt die Methode dar, die das BeforeCheck-Ereignis, das BeforeCollapse-Ereignis, das BeforeExpand-Ereignis oder das BeforeSelect-Ereignis von TreeView behandelt.
Namespace: System.Windows.Forms
Assembly: System.Windows.Forms (in system.windows.forms.dll)
Syntax
'Declaration
Public Delegate Sub TreeViewCancelEventHandler ( _
sender As Object, _
e As TreeViewCancelEventArgs _
)
'Usage
Dim instance As New TreeViewCancelEventHandler(AddressOf HandlerMethod)
public delegate void TreeViewCancelEventHandler (
Object sender,
TreeViewCancelEventArgs e
)
public delegate void TreeViewCancelEventHandler (
Object^ sender,
TreeViewCancelEventArgs^ e
)
/** @delegate */
public delegate void TreeViewCancelEventHandler (
Object sender,
TreeViewCancelEventArgs e
)
JScript unterstützt die Verwendung von Delegaten, aber nicht die Deklaration von neuen Delegaten.
Parameter
- sender
Die Quelle des Ereignisses.
- e
Ein TreeViewCancelEventArgs, das die Ereignisdaten enthält.
Hinweise
Beim Erstellen eines TreeViewCancelEventArgs-Delegaten bestimmen Sie die Methode für die Ereignisbehandlung. Um das Ereignis dem Ereignishandler zuzuordnen, fügen Sie dem Ereignis eine Instanz des Delegaten hinzu. Der Ereignishandler wird bei jedem Eintreten des Ereignisses aufgerufen, sofern der Delegat nicht entfernt wird. Weitere Informationen über Ereignishandlerdelegaten finden Sie unter Ereignisse und Delegaten.
Beispiel
Im folgenden Beispiel wird das Ändern des Zustands einer TreeView veranschaulicht, um alle aktivierten Knoten anzuzeigen. Zu Beginn sind alle Knoten reduziert, und dem TreeView.BeforeExpand-Ereignis wird ein Handler zugeordnet. Anschließend werden alle Knoten erweitert. Der TreeView.BeforeExpand-Ereignishandler bestimmt, ob ein bestimmter Knoten über aktivierte untergeordnete Knoten verfügt. Wenn ein Knoten über keine aktivierten untergeordneten Knoten verfügt, wird die Erweiterung an dem Knoten beendet. Damit Knoten wieder normal über das Klicken auf das Pluszeichen neben dem Knoten erweitert werden können, wird der TreeView.BeforeExpand-Ereignishandler anschließend entfernt.
Dieses Verhalten können Sie auch durch Behandeln des TreeView.BeforeCollapse-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.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 'showCheckedNodesButton_Click
' 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 '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.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;
}
}
#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 );
}
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
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.
Versionsinformationen
.NET Framework
Unterstützt in: 2.0, 1.1, 1.0
.NET Compact Framework
Unterstützt in: 2.0, 1.0
Siehe auch
Referenz
System.Windows.Forms-Namespace
TreeViewCancelEventArgs-Klasse
TreeView-Klasse