Bagikan melalui

TreeView.BeforeCheck Kejadian

  • Referensi

Definisi

Ruang nama:
System.Windows.Forms
Rakitan:
System.Windows.Forms.dll

Terjadi sebelum kotak centang simpul pohon dicentang.

public:
 event System::Windows::Forms::TreeViewCancelEventHandler ^ BeforeCheck;
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

Jenis Acara

TreeViewCancelEventHandler

Contoh

Contoh kode berikut memperbarui semua simpul TreeNode pohon anak saat pengguna mengubah status diperiksa. Kode ini mengharuskan Anda memiliki Form dengan yang memiliki TreeNode objek di dalamnyaTreeNodeCollectionTreeView. TreeNodeCollection harus memiliki simpul pohon dengan simpul anak.

// 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

Keterangan

Catatan

TreeNode.Checked Mengatur properti dari dalam BeforeCheck atau AfterCheck peristiwa menyebabkan peristiwa dinaikkan beberapa kali dan dapat mengakibatkan perilaku yang tidak terduga. Misalnya, Anda dapat mengatur Checked properti di penanganan aktivitas saat memperbarui simpul anak secara rekursif, sehingga pengguna tidak perlu memperluas dan memeriksa masing-masing simpul satu per satu. Untuk mencegah peristiwa dinaikkan beberapa kali, tambahkan logika ke penanganan aktivitas Anda yang hanya menjalankan kode rekursif Anda jika Action properti TreeViewEventArgs tidak diatur ke TreeViewAction.Unknown.

Untuk informasi selengkapnya tentang cara menangani peristiwa, lihat Menangani dan Menaikkan Peristiwa.

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