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ItemDragEventHandler Delegate

Represents the method that will handle the ItemDrag event of a ListView or TreeView control.

Namespace:  System.Windows.Forms
Assembly:  System.Windows.Forms (in System.Windows.Forms.dll)

public delegate void ItemDragEventHandler(
	Object^ sender, 
	ItemDragEventArgs^ e
)

Parameters

sender
Type: System::Object
The source of the event.
e
Type: System.Windows.Forms::ItemDragEventArgs
An ItemDragEventArgs that contains the event data.

When you create an ItemDragEventHandler delegate, you identify the method that will handle the event. To associate the event with your event handler, add an instance of the delegate to the event. The event handler is called whenever the event occurs, unless you remove the delegate. For more information about event handler delegates, see Events and Delegates.

The following example demonstrates how to enable drag-and-drop operations within a TreeView control. In the example, any node can be dragged to another node that is not a descendant of the dragged node. The dragged node, including all of its descendant nodes, becomes a child of the destination node. When the left mouse button is used, the dragged node is moved to the destination node. When the right mouse button is used, the dragged node is copied to the destination node.


#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;

public:
   Form1()
   {
      treeView1 = gcnew TreeView;
      this->SuspendLayout();

      // Initialize treeView1.
      treeView1->AllowDrop = true;
      treeView1->Dock = DockStyle::Fill;

      // Add nodes to treeView1.
      TreeNode^ node;
      for ( int x = 0; x < 3; ++x )
      {

         // Add a root node to treeView1.
         node = treeView1->Nodes->Add( String::Format( "Node{0}", x * 4 ) );
         for ( int y = 1; y < 4; ++y )
         {

            // Add a child node to the previously added node.
            node = node->Nodes->Add( String::Format( "Node{0}", x * 4 + y ) );

         }
      }

      // Add event handlers for the required drag events.
      treeView1->ItemDrag += gcnew ItemDragEventHandler( this, &Form1::treeView1_ItemDrag );
      treeView1->DragEnter += gcnew DragEventHandler( this, &Form1::treeView1_DragEnter );
      treeView1->DragOver += gcnew DragEventHandler( this, &Form1::treeView1_DragOver );
      treeView1->DragDrop += gcnew DragEventHandler( this, &Form1::treeView1_DragDrop );

      // Initialize the form.
      this->ClientSize = System::Drawing::Size( 292, 273 );
      this->Controls->Add( treeView1 );
      this->ResumeLayout( false );
   }

private:
   void treeView1_ItemDrag( Object^ /*sender*/, ItemDragEventArgs^ e )
   {

      // Move the dragged node when the left mouse button is used.
      if ( e->Button == ::MouseButtons::Left )
      {
         DoDragDrop( e->Item, DragDropEffects::Move );
      }
      // Copy the dragged node when the right mouse button is used.
      else

      // Copy the dragged node when the right mouse button is used.
      if ( e->Button == ::MouseButtons::Right )
      {
         DoDragDrop( e->Item, DragDropEffects::Copy );
      }
   }

   // Set the target drop effect to the effect 
   // specified in the ItemDrag event handler.
   void treeView1_DragEnter( Object^ /*sender*/, DragEventArgs^ e )
   {
      e->Effect = e->AllowedEffect;
   }

   // Select the node under the mouse pointer to indicate the 
   // expected drop location.
   void treeView1_DragOver( Object^ /*sender*/, DragEventArgs^ e )
   {
      // Retrieve the client coordinates of the mouse position.
      Point targetPoint = treeView1->PointToClient( Point(e->X,e->Y) );

      // Select the node at the mouse position.
      treeView1->SelectedNode = treeView1->GetNodeAt( targetPoint );
   }

   void treeView1_DragDrop( Object^ /*sender*/, DragEventArgs^ e )
   {
      // Retrieve the client coordinates of the drop location.
      Point targetPoint = treeView1->PointToClient( Point(e->X,e->Y) );

      // Retrieve the node at the drop location.
      TreeNode^ targetNode = treeView1->GetNodeAt( targetPoint );

      // Retrieve the node that was dragged.
      TreeNode^ draggedNode = dynamic_cast<TreeNode^>(e->Data->GetData( TreeNode::typeid ));

      // Confirm that the node at the drop location is not 
      // the dragged node or a descendant of the dragged node.
      if (  !draggedNode->Equals( targetNode ) &&  !ContainsNode( draggedNode, targetNode ) )
      {

         // If it is a move operation, remove the node from its current 
         // location and add it to the node at the drop location.
         if ( e->Effect == DragDropEffects::Move )
         {
            draggedNode->Remove();
            targetNode->Nodes->Add( draggedNode );
         }
         // If it is a copy operation, clone the dragged node 
         // and add it to the node at the drop location.
         else

         // If it is a copy operation, clone the dragged node 
         // and add it to the node at the drop location.
         if ( e->Effect == DragDropEffects::Copy )
         {
            targetNode->Nodes->Add( dynamic_cast<TreeNode^>(draggedNode->Clone()) );
         }

         // Expand the node at the location 
         // to show the dropped node.
         targetNode->Expand();
      }
   }

   // Determine whether one node is a parent 
   // or ancestor of a second node.
   bool ContainsNode( TreeNode^ node1, TreeNode^ node2 )
   {
      // Check the parent node of the second node.
      if ( node2->Parent == nullptr )
            return false;

      if ( node2->Parent->Equals( node1 ) )
            return true;

      // If the parent node is not null or equal to the first node, 
      // call the ContainsNode method recursively using the parent of 
      // the second node.
      return ContainsNode( node1, node2->Parent );
   }
};

[STAThread]
int main()
{
   Application::Run( gcnew Form1 );
}


.NET Framework

Supported in: 4, 3.5, 3.0, 2.0, 1.1, 1.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows XP SP2 x64 Edition, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

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