TreeView.BeforeCheck TreeView.BeforeCheck TreeView.BeforeCheck TreeView.BeforeCheck Event

Definición

Se produce antes de activarse la casilla del nodo de árbol.Occurs before the tree node check box is checked.

public:
 event System::Windows::Forms::TreeViewCancelEventHandler ^ BeforeCheck;
public event System.Windows.Forms.TreeViewCancelEventHandler BeforeCheck;
member this.BeforeCheck : System.Windows.Forms.TreeViewCancelEventHandler 
Public Custom Event BeforeCheck As TreeViewCancelEventHandler 

Ejemplos

En el ejemplo de código siguiente se actualiza todos los nodos de árbol secundarios de un TreeNode cuando el usuario cambia su estado de activación.The following code example updates all the child tree nodes of a TreeNode when the user changes its checked state. Este código requiere que haya un Form con un TreeView cuya TreeNode objetos en su TreeNodeCollection.This code requires that you have a Form with a TreeView that has TreeNode objects in its TreeNodeCollection. El TreeNodeCollection deben tener nodos de árbol con nodos secundarios.The TreeNodeCollection should have tree nodes with child nodes.

// Updates all child tree nodes recursively.
void CheckAllChildNodes( TreeNode^ treeNode, bool nodeChecked )
{
   IEnumerator^ myEnum = treeNode->Nodes->GetEnumerator();
   while ( myEnum->MoveNext() )
   {
      TreeNode^ node = safe_cast<TreeNode^>(myEnum->Current);
      node->Checked = nodeChecked;
      if ( node->Nodes->Count > 0 )
      {
         
         // If the current node has child nodes, call the CheckAllChildsNodes method recursively.
         this->CheckAllChildNodes( node, nodeChecked );
      }
   }
}

// NOTE   This code can be added to the BeforeCheck event handler instead of the AfterCheck event.
// After a tree node's Checked property is changed, all its child nodes are updated to the same value.
void node_AfterCheck( Object^ /*sender*/, TreeViewEventArgs^ e )
{
   // The code only executes if the user caused the checked state to change.
   if ( e->Action != TreeViewAction::Unknown )
   {
      if ( e->Node->Nodes->Count > 0 )
      {
         /* Calls the CheckAllChildNodes method, passing in the current
             Checked value of the TreeNode whose checked state changed. */
         this->CheckAllChildNodes( e->Node, e->Node->Checked );
      }
   }
}
// Updates all child tree nodes recursively.
private void CheckAllChildNodes(TreeNode treeNode, bool nodeChecked)
{
   foreach(TreeNode node in treeNode.Nodes)
   {
      node.Checked = nodeChecked;
      if(node.Nodes.Count > 0)
      {
         // If the current node has child nodes, call the CheckAllChildsNodes method recursively.
         this.CheckAllChildNodes(node, nodeChecked);
      }
   }
}

// NOTE   This code can be added to the BeforeCheck event handler instead of the AfterCheck event.
// After a tree node's Checked property is changed, all its child nodes are updated to the same value.
private void node_AfterCheck(object sender, TreeViewEventArgs e)
{
   // The code only executes if the user caused the checked state to change.
   if(e.Action != TreeViewAction.Unknown)
   {
      if(e.Node.Nodes.Count > 0)
      {
         /* Calls the CheckAllChildNodes method, passing in the current 
         Checked value of the TreeNode whose checked state changed. */
         this.CheckAllChildNodes(e.Node, e.Node.Checked);
      }
   }
}
' Updates all child tree nodes recursively.
Private Sub CheckAllChildNodes(treeNode As TreeNode, nodeChecked As Boolean)
   Dim node As TreeNode
   For Each node In  treeNode.Nodes 
      node.Checked = nodeChecked
      If node.Nodes.Count > 0 Then
         ' If the current node has child nodes, call the CheckAllChildsNodes method recursively.
         Me.CheckAllChildNodes(node, nodeChecked)
      End If
   Next node
End Sub
      
' NOTE   This code can be added to the BeforeCheck event handler instead of the AfterCheck event.
' After a tree node's Checked property is changed, all its child nodes are updated to the same value.
Private Sub node_AfterCheck(sender As Object, e As TreeViewEventArgs) Handles treeView1.AfterCheck
   ' The code only executes if the user caused the checked state to change.
   If e.Action <> TreeViewAction.Unknown Then 
      If e.Node.Nodes.Count > 0 Then
         ' Calls the CheckAllChildNodes method, passing in the current 
         ' Checked value of the TreeNode whose checked state changed. 
         Me.CheckAllChildNodes(e.Node, e.Node.Checked)
      End If
   End If
End Sub 

Comentarios

Nota

Establecer el TreeNode.Checked propiedad desde la BeforeCheck o AfterCheck eventos hace que el evento se provoca varias veces y puede provocar un comportamiento inesperado.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. Por ejemplo, puede establecer el Checked propiedad en el controlador de eventos cuando se están actualizando los nodos secundarios, de forma recursiva para que el usuario no tiene que expandir y comprobar cada una de ellas individualmente.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. Para evitar que el evento que se va a provocar varias veces, agregar lógica al controlador de eventos que solo se ejecuta el código recursivo si la Action propiedad de la TreeViewEventArgs no está establecido en TreeViewAction.Unknown.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.

Para obtener más información acerca de cómo controlar eventos, vea controlar y provocar eventos.For more information about how to handle events, see Handling and Raising Events.

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