Control.DoDragDrop Metoda

public:
 System::Windows::Forms::DragDropEffects DoDragDrop(System::Object ^ data, System::Windows::Forms::DragDropEffects allowedEffects, System::Drawing::Bitmap ^ dragImage, System::Drawing::Point cursorOffset, bool useDefaultDragImage);

public System.Windows.Forms.DragDropEffects DoDragDrop (object data, System.Windows.Forms.DragDropEffects allowedEffects, System.Drawing.Bitmap? dragImage, System.Drawing.Point cursorOffset, bool useDefaultDragImage);

member this.DoDragDrop : obj * System.Windows.Forms.DragDropEffects * System.Drawing.Bitmap * System.Drawing.Point * bool -> System.Windows.Forms.DragDropEffects

Public Function DoDragDrop (data As Object, allowedEffects As DragDropEffects, dragImage As Bitmap, cursorOffset As Point, useDefaultDragImage As Boolean) As DragDropEffects

Parametry

Návraty

Hodnota z DragDropEffects výčtu, která představuje konečný efekt, který byl proveden během operace přetažení.

Poznámky

Parametr allowedEffects určuje, ke kterým operacím přetažení může dojít. Pokud operace přetažení potřebuje spolupracovat s aplikacemi v jiném procesu, data by měla být základní spravovaná třída (String, Bitmapnebo Metafile) nebo některá Object, která implementuje ISerializable. data může být také libovolný Object, který implementuje IDataObject. dragImage je rastrový obrázek, který se zobrazí během operace přetažení a cursorOffset určuje umístění kurzoru v dragImage, což je posun od levého horního rohu. Zadejte true pro useDefaultDragImage použít obrázek přetažení vrstvy okna s velikostí 96 × 96; jinak false. Všimněte si, že vnější okraje dragImage se prolínají, pokud šířka nebo výška obrázku překročí 300 pixelů.

Vzhledem k tomu, že DoDragDrop(Object, DragDropEffects, Bitmap, Point, Boolean) vždy provádí krok násobení RGB při výpočtu alfa hodnoty, měli byste vždy předat Bitmap bez premultiplied alfa blendingu. Výsledkem žádné chyby nebude předání Bitmap s premultiplied alfa blending, ale tato metoda ji znovu vynásobí a výslednou alfa hodnotu zdvojnásobí.

public:
 System::Windows::Forms::DragDropEffects DoDragDrop(System::Object ^ data, System::Windows::Forms::DragDropEffects allowedEffects);

public System.Windows.Forms.DragDropEffects DoDragDrop (object data, System.Windows.Forms.DragDropEffects allowedEffects);

member this.DoDragDrop : obj * System.Windows.Forms.DragDropEffects -> System.Windows.Forms.DragDropEffects

Public Function DoDragDrop (data As Object, allowedEffects As DragDropEffects) As DragDropEffects

Parametry

Návraty

Hodnota z DragDropEffects výčtu, která představuje konečný efekt, který byl proveden během operace přetažení.

Příklady

Následující příklad kódu ukazuje operaci přetažení mezi dvěma ovládacími prvky ListBox. Příklad volá metodu DoDragDrop při spuštění akce přetažení. Akce přetažení se spustí, pokud se během události MouseDown přesunulo více než SystemInformation.DragSize z umístění myši. Metoda IndexFromPoint slouží k určení indexu položky, která se má přetáhnout během události MouseDown.

Příklad také ukazuje použití vlastních kurzorů pro operaci přetažení. Příklad vyžaduje, aby byly dva soubory kurzoru, 3dwarro.cur a 3dwno.cur, existují v adresáři aplikace pro vlastní přetažení a bez-drop kurzory, v uvedeném pořadí. Vlastní kurzory se použijí, pokud je zaškrtnuté UseCustomCursorsCheckCheckBox. Vlastní kurzory jsou nastaveny v obslužné rutině události GiveFeedback.

Stav klávesnice se vyhodnocuje v obslužné rutině události DragOver pro správnou ListBox, aby bylo možné určit, jaké operace přetažení bude založená na stavu kláves SHIFT, CTRL, ALT nebo CTRL+ALT. Umístění v ListBox, kde dojde k poklesu, je také určeno během DragOver události. Pokud data, která chcete odstranit, nejsou String, je DragEventArgs.Effect nastavena na None v DragDropEffects. Nakonec se stav poklesu zobrazí v DropLocationLabelLabel.

Data, která se mají odstranit pro správný ListBox, se určují v obslužné rutině události DragDrop a hodnota String se přidá na příslušné místo v ListBox. Pokud se operace přetažení přesune mimo hranice formuláře, operace přetažení se zruší v obslužné rutině události QueryContinueDrag.

using namespace System;
using namespace System::Drawing;
using namespace System::Windows::Forms;

namespace Snip_DragNDrop
{
   public ref class Form1: public System::Windows::Forms::Form
   {
   private:
      System::Windows::Forms::ListBox^ ListDragSource;
      System::Windows::Forms::ListBox^ ListDragTarget;
      System::Windows::Forms::CheckBox^ UseCustomCursorsCheck;
      System::Windows::Forms::Label ^ DropLocationLabel;
      Int32 indexOfItemUnderMouseToDrag;
      Int32 indexOfItemUnderMouseToDrop;
      Rectangle dragBoxFromMouseDown;
      Point screenOffset;
      System::Windows::Forms::Cursor^ MyNoDropCursor;
      System::Windows::Forms::Cursor^ MyNormalCursor;

   public:
      Form1()
      {
         this->ListDragSource = gcnew System::Windows::Forms::ListBox;
         this->ListDragTarget = gcnew System::Windows::Forms::ListBox;
         this->UseCustomCursorsCheck = gcnew System::Windows::Forms::CheckBox;
         this->DropLocationLabel = gcnew System::Windows::Forms::Label;
         this->SuspendLayout();
         
         // ListDragSource
         array<Object^>^temp0 = {"five","six","seven","eight","nine","ten"};
         this->ListDragSource->Items->AddRange( temp0 );
         this->ListDragSource->Location = System::Drawing::Point( 10, 17 );
         this->ListDragSource->Size = System::Drawing::Size( 120, 225 );
         this->ListDragSource->MouseDown += gcnew System::Windows::Forms::MouseEventHandler( this, &Form1::ListDragSource_MouseDown );
         this->ListDragSource->QueryContinueDrag += gcnew System::Windows::Forms::QueryContinueDragEventHandler( this, &Form1::ListDragSource_QueryContinueDrag );
         this->ListDragSource->MouseUp += gcnew System::Windows::Forms::MouseEventHandler( this, &Form1::ListDragSource_MouseUp );
         this->ListDragSource->MouseMove += gcnew System::Windows::Forms::MouseEventHandler( this, &Form1::ListDragSource_MouseMove );
         this->ListDragSource->GiveFeedback += gcnew System::Windows::Forms::GiveFeedbackEventHandler( this, &Form1::ListDragSource_GiveFeedback );
         
         // ListDragTarget
         this->ListDragTarget->AllowDrop = true;
         this->ListDragTarget->Location = System::Drawing::Point( 154, 17 );
         this->ListDragTarget->Size = System::Drawing::Size( 120, 225 );
         this->ListDragTarget->DragOver += gcnew System::Windows::Forms::DragEventHandler( this, &Form1::ListDragTarget_DragOver );
         this->ListDragTarget->DragDrop += gcnew System::Windows::Forms::DragEventHandler( this, &Form1::ListDragTarget_DragDrop );
         this->ListDragTarget->DragEnter += gcnew System::Windows::Forms::DragEventHandler( this, &Form1::ListDragTarget_DragEnter );
         this->ListDragTarget->DragLeave += gcnew System::EventHandler( this, &Form1::ListDragTarget_DragLeave );
         
         // UseCustomCursorsCheck
         this->UseCustomCursorsCheck->Location = System::Drawing::Point( 10, 243 );
         this->UseCustomCursorsCheck->Size = System::Drawing::Size( 137, 24 );
         this->UseCustomCursorsCheck->Text = "Use Custom Cursors";
         
         // DropLocationLabel
         this->DropLocationLabel->Location = System::Drawing::Point( 154, 245 );
         this->DropLocationLabel->Size = System::Drawing::Size( 137, 24 );
         this->DropLocationLabel->Text = "None";
         
         // Form1
         this->ClientSize = System::Drawing::Size( 292, 270 );
         array<System::Windows::Forms::Control^>^formControls = {this->ListDragSource,this->ListDragTarget,this->UseCustomCursorsCheck,this->DropLocationLabel};
         this->Controls->AddRange( formControls );
         this->Text = "drag-and-drop Example";
         this->ResumeLayout( false );
      }


   private:
      void ListDragSource_MouseDown( Object^ /*sender*/, System::Windows::Forms::MouseEventArgs^ e )
      {
         
         // Get the index of the item the mouse is below.
         indexOfItemUnderMouseToDrag = this->ListDragSource->IndexFromPoint( e->X, e->Y );
         if ( indexOfItemUnderMouseToDrag != ListBox::NoMatches )
         {
            
            // Remember the point where the mouse down occurred. The DragSize indicates
            // the size that the mouse can move before a drag event should be started.
            System::Drawing::Size dragSize = SystemInformation::DragSize;
            
            // Create a rectangle using the DragSize, with the mouse position being
            // at the center of the rectangle.
            dragBoxFromMouseDown = Rectangle(Point(e->X - (dragSize.Width / 2),e->Y - (dragSize.Height / 2)),dragSize);
         }
         else
                  dragBoxFromMouseDown = Rectangle::Empty;

         
         // Reset the rectangle if the mouse is not over an item in the ListBox.
      }

      void ListDragSource_MouseUp( Object^ /*sender*/, System::Windows::Forms::MouseEventArgs^ /*e*/ )
      {
         
         // Reset the drag rectangle when the mouse button is raised.
         dragBoxFromMouseDown = Rectangle::Empty;
      }


      void ListDragSource_MouseMove( Object^ /*sender*/, System::Windows::Forms::MouseEventArgs^ e )
      {
         if ( (e->Button & ::MouseButtons::Left) == ::MouseButtons::Left )
         {
            
            // If the mouse moves outside the rectangle, start the drag.
            if ( dragBoxFromMouseDown != Rectangle::Empty &&  !dragBoxFromMouseDown.Contains( e->X, e->Y ) )
            {
               
               // Create custom cursors for the drag-and-drop operation.
               try
               {
                  MyNormalCursor = gcnew System::Windows::Forms::Cursor( "3dwarro.cur" );
                  MyNoDropCursor = gcnew System::Windows::Forms::Cursor( "3dwno.cur" );
               }
               catch ( Exception^ ) 
               {
                  // An error occurred while attempting to load the cursors, so use
                  // the standard cursors.
                  this->UseCustomCursorsCheck->Checked = false;
               }
               __finally
               {                  
                  // The screenOffset is used to account for any desktop bands
                  // that may be at the top or left side of the screen when
                  // determining when to cancel the drag drop operation.
                  screenOffset = SystemInformation::WorkingArea.Location;
                  
                  // Proceed with the drag-and-drop, passing in the list item.
                  DragDropEffects dropEffect = this->ListDragSource->DoDragDrop( ListDragSource->Items[ indexOfItemUnderMouseToDrag ], static_cast<DragDropEffects>(DragDropEffects::All | DragDropEffects::Link) );
                  
                  // If the drag operation was a move then remove the item.
                  if ( dropEffect == DragDropEffects::Move )
                  {
                     ListDragSource->Items->RemoveAt( indexOfItemUnderMouseToDrag );
                     
                     // Selects the previous item in the list as long as the list has an item.
                     if ( indexOfItemUnderMouseToDrag > 0 )
                                          ListDragSource->SelectedIndex = indexOfItemUnderMouseToDrag - 1;
                     else
                     if ( ListDragSource->Items->Count > 0 )
                                          
                     // Selects the first item.
                     ListDragSource->SelectedIndex = 0;
                  }
                  
                  // Dispose of the cursors since they are no longer needed.
                  if ( MyNormalCursor != nullptr )
                                    delete MyNormalCursor;
                  if ( MyNoDropCursor != nullptr )
                                    delete MyNoDropCursor;
               }
            }
         }
      }

      void ListDragSource_GiveFeedback( Object^ /*sender*/, System::Windows::Forms::GiveFeedbackEventArgs^ e )
      {
         // Use custom cursors if the check box is checked.
         if ( UseCustomCursorsCheck->Checked )
         {
            // Sets the custom cursor based upon the effect.
            e->UseDefaultCursors = false;
            if ( (e->Effect & DragDropEffects::Move) == DragDropEffects::Move )
                        ::Cursor::Current = MyNormalCursor;
            else
                        ::Cursor::Current = MyNoDropCursor;
         }
      }

      void ListDragTarget_DragOver( Object^ /*sender*/, System::Windows::Forms::DragEventArgs^ e )
      {
         // Determine whether string data exists in the drop data. If not, then
         // the drop effect reflects that the drop cannot occur.
         if (  !e->Data->GetDataPresent( System::String::typeid ) )
         {
            e->Effect = DragDropEffects::None;
            DropLocationLabel->Text = "None - no string data.";
            return;
         }

         // Set the effect based upon the KeyState.
         if ( (e->KeyState & (8 + 32)) == (8 + 32) && ((e->AllowedEffect & DragDropEffects::Link) == DragDropEffects::Link) )
         {
            // KeyState 8 + 32 = CTRL + ALT
            // Link drag-and-drop effect.
            e->Effect = DragDropEffects::Link;
         }
         else
         if ( (e->KeyState & 32) == 32 && ((e->AllowedEffect & DragDropEffects::Link) == DragDropEffects::Link) )
         {
            // ALT KeyState for link.
            e->Effect = DragDropEffects::Link;
         }
         else
         if ( (e->KeyState & 4) == 4 && ((e->AllowedEffect & DragDropEffects::Move) == DragDropEffects::Move) )
         {
            // SHIFT KeyState for move.
            e->Effect = DragDropEffects::Move;
         }
         else
         if ( (e->KeyState & 8) == 8 && ((e->AllowedEffect & DragDropEffects::Copy) == DragDropEffects::Copy) )
         {
            // CTRL KeyState for copy.
            e->Effect = DragDropEffects::Copy;
         }
         else
         if ( (e->AllowedEffect & DragDropEffects::Move) == DragDropEffects::Move )
         {
            // By default, the drop action should be move, if allowed.
            e->Effect = DragDropEffects::Move;
         }
         else
                  e->Effect = DragDropEffects::None;





         
         // Get the index of the item the mouse is below.
         // The mouse locations are relative to the screen, so they must be
         // converted to client coordinates.
         indexOfItemUnderMouseToDrop = ListDragTarget->IndexFromPoint( ListDragTarget->PointToClient( Point(e->X,e->Y) ) );
         
         // Updates the label text.
         if ( indexOfItemUnderMouseToDrop != ListBox::NoMatches )
         {
            DropLocationLabel->Text = String::Concat( "Drops before item # ", (indexOfItemUnderMouseToDrop + 1) );
         }
         else
                  DropLocationLabel->Text = "Drops at the end.";
      }

      void ListDragTarget_DragDrop( Object^ /*sender*/, System::Windows::Forms::DragEventArgs^ e )
      {
         // Ensure that the list item index is contained in the data.
         if ( e->Data->GetDataPresent( System::String::typeid ) )
         {
            Object^ item = dynamic_cast<Object^>(e->Data->GetData( System::String::typeid ));
            
            // Perform drag-and-drop, depending upon the effect.
            if ( e->Effect == DragDropEffects::Copy || e->Effect == DragDropEffects::Move )
            {
               // Insert the item.
               if ( indexOfItemUnderMouseToDrop != ListBox::NoMatches )
                              ListDragTarget->Items->Insert( indexOfItemUnderMouseToDrop, item );
               else
                              ListDragTarget->Items->Add( item );
            }
         }

         // Reset the label text.
         DropLocationLabel->Text = "None";
      }

      void ListDragSource_QueryContinueDrag( Object^ sender, System::Windows::Forms::QueryContinueDragEventArgs^ e )
      {
         // Cancel the drag if the mouse moves off the form.
         ListBox^ lb = dynamic_cast<ListBox^>(sender);
         if ( lb != nullptr )
         {
            Form^ f = lb->FindForm();

            // Cancel the drag if the mouse moves off the form. The screenOffset
            // takes into account any desktop bands that may be at the top or left
            // side of the screen.
            if ( ((Control::MousePosition.X - screenOffset.X) < f->DesktopBounds.Left) || ((Control::MousePosition.X - screenOffset.X) > f->DesktopBounds.Right) || ((Control::MousePosition.Y - screenOffset.Y) < f->DesktopBounds.Top) || ((Control::MousePosition.Y - screenOffset.Y) > f->DesktopBounds.Bottom) )
            {
               e->Action = DragAction::Cancel;
            }
         }
      }

      void ListDragTarget_DragEnter( Object^ /*sender*/, System::Windows::Forms::DragEventArgs^ /*e*/ )
      {
         // Reset the label text.
         DropLocationLabel->Text = "None";
      }

      void ListDragTarget_DragLeave( Object^ /*sender*/, System::EventArgs^ /*e*/ )
      {
        // Reset the label text.
         DropLocationLabel->Text = "None";
      }
   };
}

/// The main entry point for the application.

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

using System;
using System.Drawing;
using System.Windows.Forms;

namespace Snip_DragNDrop
{
    public class Form1 : Form
    {
        private ListBox ListDragSource;
        private ListBox ListDragTarget;
        private CheckBox UseCustomCursorsCheck;
        private Label DropLocationLabel;

        private int indexOfItemUnderMouseToDrag;
        private int indexOfItemUnderMouseToDrop;

        private Rectangle dragBoxFromMouseDown;
        private Point screenOffset;

        private Cursor MyNoDropCursor;
        private Cursor MyNormalCursor;

        // The main entry point for the application.
        [STAThread]
        static void Main()
        {
            Application.Run(new Form1());
        }

        public Form1()
        {
            this.ListDragSource = new ListBox();
            this.ListDragTarget = new ListBox();
            this.UseCustomCursorsCheck = new CheckBox();
            this.DropLocationLabel = new Label();

            this.SuspendLayout();

            // ListDragSource
            this.ListDragSource.Items.AddRange(new object[] {"one", "two", "three", "four",
                                                             "five", "six", "seven", "eight",
                                                             "nine", "ten"});
            this.ListDragSource.Location = new Point(10, 17);
            this.ListDragSource.Size = new Size(120, 225);
            this.ListDragSource.MouseDown += this.ListDragSource_MouseDown;
            this.ListDragSource.QueryContinueDrag += this.ListDragSource_QueryContinueDrag;
            this.ListDragSource.MouseUp += this.ListDragSource_MouseUp;
            this.ListDragSource.MouseMove += this.ListDragSource_MouseMove;
            this.ListDragSource.GiveFeedback += this.ListDragSource_GiveFeedback;

            // ListDragTarget
            this.ListDragTarget.AllowDrop = true;
            this.ListDragTarget.Location = new Point(154, 17);
            this.ListDragTarget.Size = new Size(120, 225);
            this.ListDragTarget.DragOver += this.ListDragTarget_DragOver;
            this.ListDragTarget.DragDrop += this.ListDragTarget_DragDrop;
            this.ListDragTarget.DragEnter += this.ListDragTarget_DragEnter;
            this.ListDragTarget.DragLeave += this.ListDragTarget_DragLeave;

            // UseCustomCursorsCheck
            this.UseCustomCursorsCheck.Location = new Point(10, 243);
            this.UseCustomCursorsCheck.Size = new Size(137, 24);
            this.UseCustomCursorsCheck.Text = "Use Custom Cursors";

            // DropLocationLabel
            this.DropLocationLabel.Location = new Point(154, 245);
            this.DropLocationLabel.Size = new Size(137, 24);
            this.DropLocationLabel.Text = "None";

            // Form1
            this.ClientSize = new Size(292, 270);
            this.Controls.AddRange(new Control[] {
                this.ListDragSource,
                this.ListDragTarget,
                this.UseCustomCursorsCheck,
                this.DropLocationLabel});
            this.Text = "drag-and-drop Example";

            this.ResumeLayout(false);
        }

        private void ListDragSource_MouseDown(object sender, MouseEventArgs e)
        {
            // Get the index of the item the mouse is below.
            indexOfItemUnderMouseToDrag = ListDragSource.IndexFromPoint(e.X, e.Y);

            if (indexOfItemUnderMouseToDrag != ListBox.NoMatches)
            {
                // Remember the point where the mouse down occurred. The DragSize indicates
                // the size that the mouse can move before a drag event should be started.
                Size dragSize = SystemInformation.DragSize;

                // Create a rectangle using the DragSize, with the mouse position being
                // at the center of the rectangle.
                dragBoxFromMouseDown = new Rectangle(
                    new Point(e.X - (dragSize.Width / 2),
                              e.Y - (dragSize.Height / 2)),
                    dragSize);
            }
            else
            {
                // Reset the rectangle if the mouse is not over an item in the ListBox.
                dragBoxFromMouseDown = Rectangle.Empty;
            }
        }

        private void ListDragSource_MouseUp(object sender, MouseEventArgs e)
        {
            // Reset the drag rectangle when the mouse button is raised.
            dragBoxFromMouseDown = Rectangle.Empty;
        }

        private void ListDragSource_MouseMove(object sender, MouseEventArgs e)
        {
            if ((e.Button & MouseButtons.Left) == MouseButtons.Left)
            {
                // If the mouse moves outside the rectangle, start the drag.
                if (dragBoxFromMouseDown != Rectangle.Empty &&
                    !dragBoxFromMouseDown.Contains(e.X, e.Y))
                {
                    // Create custom cursors for the drag-and-drop operation.
                    try
                    {
                        MyNormalCursor = new Cursor("3dwarro.cur");
                        MyNoDropCursor = new Cursor("3dwno.cur");
                    }
                    catch
                    {
                        // An error occurred while attempting to load the cursors, so use
                        // standard cursors.
                        UseCustomCursorsCheck.Checked = false;
                    }
                    finally
                    {
                        // The screenOffset is used to account for any desktop bands 
                        // that may be at the top or left side of the screen when 
                        // determining when to cancel the drag drop operation.
                        screenOffset = SystemInformation.WorkingArea.Location;

                        // Proceed with the drag-and-drop, passing in the list item.
                        DragDropEffects dropEffect = ListDragSource.DoDragDrop(ListDragSource.Items[indexOfItemUnderMouseToDrag], DragDropEffects.All | DragDropEffects.Link);

                        // If the drag operation was a move then remove the item.
                        if (dropEffect == DragDropEffects.Move)
                        {
                            ListDragSource.Items.RemoveAt(indexOfItemUnderMouseToDrag);

                            // Selects the previous item in the list as long as the list has an item.
                            if (indexOfItemUnderMouseToDrag > 0)
                                ListDragSource.SelectedIndex = indexOfItemUnderMouseToDrag - 1;

                            else if (ListDragSource.Items.Count > 0)
                                // Selects the first item.
                                ListDragSource.SelectedIndex = 0;
                        }

                        // Dispose of the cursors since they are no longer needed.
                        if (MyNormalCursor != null)
                            MyNormalCursor.Dispose();

                        if (MyNoDropCursor != null)
                            MyNoDropCursor.Dispose();
                    }
                }
            }
        }
        private void ListDragSource_GiveFeedback(object sender, GiveFeedbackEventArgs e)
        {
            // Use custom cursors if the check box is checked.
            if (UseCustomCursorsCheck.Checked)
            {
                // Sets the custom cursor based upon the effect.
                e.UseDefaultCursors = false;
                if ((e.Effect & DragDropEffects.Move) == DragDropEffects.Move)
                    Cursor.Current = MyNormalCursor;
                else
                    Cursor.Current = MyNoDropCursor;
            }
        }
        private void ListDragTarget_DragOver(object sender, DragEventArgs e)
        {
            // Determine whether string data exists in the drop data. If not, then
            // the drop effect reflects that the drop cannot occur.
            if (!e.Data.GetDataPresent(typeof(System.String)))
            {
                e.Effect = DragDropEffects.None;
                DropLocationLabel.Text = "None - no string data.";
                return;
            }

            // Set the effect based upon the KeyState.
            if ((e.KeyState & (8 + 32)) == (8 + 32) &&
                (e.AllowedEffect & DragDropEffects.Link) == DragDropEffects.Link)
            {
                // KeyState 8 + 32 = CTRL + ALT

                // Link drag-and-drop effect.
                e.Effect = DragDropEffects.Link;
            }
            else if ((e.KeyState & 32) == 32 &&
                (e.AllowedEffect & DragDropEffects.Link) == DragDropEffects.Link)
            {
                // ALT KeyState for link.
                e.Effect = DragDropEffects.Link;
            }
            else if ((e.KeyState & 4) == 4 &&
                (e.AllowedEffect & DragDropEffects.Move) == DragDropEffects.Move)
            {
                // SHIFT KeyState for move.
                e.Effect = DragDropEffects.Move;
            }
            else if ((e.KeyState & 8) == 8 &&
                (e.AllowedEffect & DragDropEffects.Copy) == DragDropEffects.Copy)
            {
                // CTRL KeyState for copy.
                e.Effect = DragDropEffects.Copy;
            }
            else if ((e.AllowedEffect & DragDropEffects.Move) == DragDropEffects.Move)
            {
                // By default, the drop action should be move, if allowed.
                e.Effect = DragDropEffects.Move;
            }
            else
            {
                e.Effect = DragDropEffects.None;
            }

            // Get the index of the item the mouse is below. 

            // The mouse locations are relative to the screen, so they must be 
            // converted to client coordinates.

            indexOfItemUnderMouseToDrop =
                ListDragTarget.IndexFromPoint(ListDragTarget.PointToClient(new Point(e.X, e.Y)));

            // Updates the label text.
            if (indexOfItemUnderMouseToDrop != ListBox.NoMatches)
            {
                DropLocationLabel.Text = "Drops before item #" + (indexOfItemUnderMouseToDrop + 1);
            }
            else
            {
                DropLocationLabel.Text = "Drops at the end.";
            }
        }
        private void ListDragTarget_DragDrop(object sender, DragEventArgs e)
        {
            // Ensure that the list item index is contained in the data.
            if (e.Data.GetDataPresent(typeof(System.String)))
            {
                Object item = e.Data.GetData(typeof(System.String));

                // Perform drag-and-drop, depending upon the effect.
                if (e.Effect == DragDropEffects.Copy ||
                    e.Effect == DragDropEffects.Move)
                {
                    // Insert the item.
                    if (indexOfItemUnderMouseToDrop != ListBox.NoMatches)
                        ListDragTarget.Items.Insert(indexOfItemUnderMouseToDrop, item);
                    else
                        ListDragTarget.Items.Add(item);
                }
            }
            // Reset the label text.
            DropLocationLabel.Text = "None";
        }
        private void ListDragSource_QueryContinueDrag(object sender, QueryContinueDragEventArgs e)
        {
            // Cancel the drag if the mouse moves off the form.
            ListBox lb = sender as ListBox;

            if (lb != null)
            {
                Form f = lb.FindForm();

                // Cancel the drag if the mouse moves off the form. The screenOffset
                // takes into account any desktop bands that may be at the top or left
                // side of the screen.
                if (((Control.MousePosition.X - screenOffset.X) < f.DesktopBounds.Left) ||
                    ((Control.MousePosition.X - screenOffset.X) > f.DesktopBounds.Right) ||
                    ((Control.MousePosition.Y - screenOffset.Y) < f.DesktopBounds.Top) ||
                    ((Control.MousePosition.Y - screenOffset.Y) > f.DesktopBounds.Bottom))
                {
                    e.Action = DragAction.Cancel;
                }
            }
        }
        private void ListDragTarget_DragEnter(object sender, DragEventArgs e)
        {
            // Reset the label text.
            DropLocationLabel.Text = "None";
        }
        private void ListDragTarget_DragLeave(object sender, EventArgs e)
        {
            // Reset the label text.
            DropLocationLabel.Text = "None";
        }
    }
}

Imports System.Drawing
Imports System.Windows.Forms

Public NotInheritable Class Form1
    Inherits Form

    Friend WithEvents ListDragSource As ListBox
    Friend WithEvents ListDragTarget As ListBox
    Friend WithEvents UseCustomCursorsCheck As CheckBox
    Friend WithEvents DropLocationLabel As Label

    Private indexOfItemUnderMouseToDrag As Integer
    Private indexOfItemUnderMouseToDrop As Integer

    Private dragBoxFromMouseDown As Rectangle
    Private screenOffset As Point

    Private MyNoDropCursor As Cursor
    Private MyNormalCursor As Cursor

    <STAThread()>
    Public Shared Sub Main()
        Application.Run(New Form1())
    End Sub

    Public Sub New()
        MyBase.New()

        Me.ListDragSource = New ListBox()
        Me.ListDragTarget = New ListBox()
        Me.UseCustomCursorsCheck = New CheckBox()
        Me.DropLocationLabel = New Label()

        Me.SuspendLayout()

        ' ListDragSource
        Me.ListDragSource.Items.AddRange(New Object() {"one", "two", "three", "four",
                                                       "five", "six", "seven", "eight",
                                                       "nine", "ten"})
        Me.ListDragSource.Location = New Point(10, 17)
        Me.ListDragSource.Size = New Size(120, 225)

        ' ListDragTarget
        Me.ListDragTarget.AllowDrop = True
        Me.ListDragTarget.Location = New Point(154, 17)
        Me.ListDragTarget.Size = New Size(120, 225)

        ' UseCustomCursorsCheck
        Me.UseCustomCursorsCheck.Location = New Point(10, 243)
        Me.UseCustomCursorsCheck.Size = New Size(137, 24)
        Me.UseCustomCursorsCheck.Text = "Use Custom Cursors"

        ' DropLocationLabel
        Me.DropLocationLabel.Location = New Point(154, 245)
        Me.DropLocationLabel.Size = New Size(137, 24)
        Me.DropLocationLabel.Text = "None"

        ' Form1
        Me.ClientSize = New Size(292, 270)
        Me.Controls.AddRange(New Control() {Me.ListDragSource,
                                            Me.ListDragTarget,
                                            Me.UseCustomCursorsCheck,
                                            Me.DropLocationLabel})

        Me.Text = "drag-and-drop Example"
        Me.ResumeLayout(False)
    End Sub

    Private Sub ListDragSource_MouseDown(ByVal sender As Object, ByVal e As MouseEventArgs) Handles ListDragSource.MouseDown
        ' Get the index of the item the mouse is below.
        indexOfItemUnderMouseToDrag = ListDragSource.IndexFromPoint(e.X, e.Y)

        If (indexOfItemUnderMouseToDrag <> ListBox.NoMatches) Then

            ' Remember the point where the mouse down occurred. The DragSize indicates
            ' the size that the mouse can move before a drag event should be started.
            Dim dragSize As Size = SystemInformation.DragSize

            ' Create a rectangle using the DragSize, with the mouse position being
            ' at the center of the rectangle.
            dragBoxFromMouseDown = New Rectangle(
              New Point(e.X - (dragSize.Width / 2), e.Y - (dragSize.Height / 2)),
              dragSize)
        Else
            ' Reset the rectangle if the mouse is not over an item in the ListBox.
            dragBoxFromMouseDown = Rectangle.Empty
        End If

    End Sub

    Private Sub ListDragSource_MouseUp(ByVal sender As Object, ByVal e As MouseEventArgs) Handles ListDragSource.MouseUp
        ' Reset the drag rectangle when the mouse button is raised.
        dragBoxFromMouseDown = Rectangle.Empty
    End Sub

    Private Sub ListDragSource_MouseMove(ByVal sender As Object, ByVal e As MouseEventArgs) Handles ListDragSource.MouseMove

        If ((e.Button And MouseButtons.Left) = MouseButtons.Left) Then

            ' If the mouse moves outside the rectangle, start the drag.
            If (Rectangle.op_Inequality(dragBoxFromMouseDown, Rectangle.Empty) And
                Not dragBoxFromMouseDown.Contains(e.X, e.Y)) Then

                ' Creates custom cursors for the drag-and-drop operation.
                Try
                    MyNormalCursor = New Cursor("3dwarro.cur")
                    MyNoDropCursor = New Cursor("3dwno.cur")

                Catch
                    ' An error occurred while attempting to load the cursors so use
                    ' standard cursors.
                    UseCustomCursorsCheck.Checked = False
                Finally
                    ' The screenOffset is used to account for any desktop bands 
                    ' that may be at the top or left side of the screen when 
                    ' determining when to cancel the drag drop operation.
                    screenOffset = SystemInformation.WorkingArea.Location

                    ' Proceed with the drag-and-drop, passing in the list item.
                    Dim dropEffect As DragDropEffects = ListDragSource.DoDragDrop(
                      ListDragSource.Items(indexOfItemUnderMouseToDrag),
                      DragDropEffects.All Or DragDropEffects.Link)

                    ' If the drag operation was a move then remove the item.
                    If (dropEffect = DragDropEffects.Move) Then
                        ListDragSource.Items.RemoveAt(indexOfItemUnderMouseToDrag)

                        ' Select the previous item in the list as long as the list has an item.
                        If (indexOfItemUnderMouseToDrag > 0) Then
                            ListDragSource.SelectedIndex = indexOfItemUnderMouseToDrag - 1

                        ElseIf (ListDragSource.Items.Count > 0) Then
                            ' Selects the first item.
                            ListDragSource.SelectedIndex = 0
                        End If
                    End If

                    ' Dispose the cursors since they are no longer needed.
                    If (Not MyNormalCursor Is Nothing) Then _
                        MyNormalCursor.Dispose()

                    If (Not MyNoDropCursor Is Nothing) Then _
                        MyNoDropCursor.Dispose()
                End Try

            End If
        End If
    End Sub
    Private Sub ListDragSource_GiveFeedback(ByVal sender As Object, ByVal e As GiveFeedbackEventArgs) Handles ListDragSource.GiveFeedback
        ' Use custom cursors if the check box is checked.
        If (UseCustomCursorsCheck.Checked) Then

            ' Set the custom cursor based upon the effect.
            e.UseDefaultCursors = False
            If ((e.Effect And DragDropEffects.Move) = DragDropEffects.Move) Then
                Cursor.Current = MyNormalCursor
            Else
                Cursor.Current = MyNoDropCursor
            End If
        End If

    End Sub

    Private Sub ListDragTarget_DragOver(ByVal sender As Object, ByVal e As DragEventArgs) Handles ListDragTarget.DragOver
        ' Determine whether string data exists in the drop data. If not, then
        ' the drop effect reflects that the drop cannot occur.
        If Not (e.Data.GetDataPresent(GetType(System.String))) Then

            e.Effect = DragDropEffects.None
            DropLocationLabel.Text = "None - no string data."
            Return
        End If

        ' Set the effect based upon the KeyState.
        If ((e.KeyState And (8 + 32)) = (8 + 32) And
            (e.AllowedEffect And DragDropEffects.Link) = DragDropEffects.Link) Then
            ' KeyState 8 + 32 = CTRL + ALT

            ' Link drag-and-drop effect.
            e.Effect = DragDropEffects.Link

        ElseIf ((e.KeyState And 32) = 32 And
            (e.AllowedEffect And DragDropEffects.Link) = DragDropEffects.Link) Then

            ' ALT KeyState for link.
            e.Effect = DragDropEffects.Link

        ElseIf ((e.KeyState And 4) = 4 And
            (e.AllowedEffect And DragDropEffects.Move) = DragDropEffects.Move) Then

            ' SHIFT KeyState for move.
            e.Effect = DragDropEffects.Move

        ElseIf ((e.KeyState And 8) = 8 And
            (e.AllowedEffect And DragDropEffects.Copy) = DragDropEffects.Copy) Then

            ' CTRL KeyState for copy.
            e.Effect = DragDropEffects.Copy

        ElseIf ((e.AllowedEffect And DragDropEffects.Move) = DragDropEffects.Move) Then

            ' By default, the drop action should be move, if allowed.
            e.Effect = DragDropEffects.Move

        Else
            e.Effect = DragDropEffects.None
        End If

        ' Gets the index of the item the mouse is below. 

        ' The mouse locations are relative to the screen, so they must be 
        ' converted to client coordinates.

        indexOfItemUnderMouseToDrop =
            ListDragTarget.IndexFromPoint(ListDragTarget.PointToClient(New Point(e.X, e.Y)))

        ' Updates the label text.
        If (indexOfItemUnderMouseToDrop <> ListBox.NoMatches) Then
            DropLocationLabel.Text = "Drops before item #" & (indexOfItemUnderMouseToDrop + 1)
        Else
            DropLocationLabel.Text = "Drops at the end."
        End If

    End Sub

    Private Sub ListDragTarget_DragDrop(ByVal sender As Object, ByVal e As DragEventArgs) Handles ListDragTarget.DragDrop
        ' Ensures that the list item index is contained in the data.

        If (e.Data.GetDataPresent(GetType(System.String))) Then

            Dim item As Object = CType(e.Data.GetData(GetType(System.String)), System.Object)

            ' Perform drag-and-drop, depending upon the effect.
            If (e.Effect = DragDropEffects.Copy Or
                e.Effect = DragDropEffects.Move) Then

                ' Insert the item.
                If (indexOfItemUnderMouseToDrop <> ListBox.NoMatches) Then
                    ListDragTarget.Items.Insert(indexOfItemUnderMouseToDrop, item)
                Else
                    ListDragTarget.Items.Add(item)

                End If
            End If
            ' Reset the label text.
            DropLocationLabel.Text = "None"
        End If
    End Sub
    Private Sub ListDragSource_QueryContinueDrag(ByVal sender As Object, ByVal e As QueryContinueDragEventArgs) Handles ListDragSource.QueryContinueDrag
        ' Cancel the drag if the mouse moves off the form.
        Dim lb As ListBox = CType(sender, ListBox)

        If (lb IsNot Nothing) Then

            Dim f As Form = lb.FindForm()

            ' Cancel the drag if the mouse moves off the form. The screenOffset
            ' takes into account any desktop bands that may be at the top or left
            ' side of the screen.
            If (((Control.MousePosition.X - screenOffset.X) < f.DesktopBounds.Left) Or
                ((Control.MousePosition.X - screenOffset.X) > f.DesktopBounds.Right) Or
                ((Control.MousePosition.Y - screenOffset.Y) < f.DesktopBounds.Top) Or
                ((Control.MousePosition.Y - screenOffset.Y) > f.DesktopBounds.Bottom)) Then

                e.Action = DragAction.Cancel
            End If
        End If
    End Sub
    Private Sub ListDragTarget_DragEnter(ByVal sender As Object, ByVal e As DragEventArgs) Handles ListDragTarget.DragEnter
        ' Reset the label text.
        DropLocationLabel.Text = "None"
    End Sub
    Private Sub ListDragTarget_DragLeave(ByVal sender As Object, ByVal e As EventArgs) Handles ListDragTarget.DragLeave
        ' Reset the label text.
        DropLocationLabel.Text = "None"
    End Sub
End Class

Následující příklad kódu ukazuje, jak pomocí DragDropEffects výčtu určit, jak se mají data přenášet mezi ovládacími prvky zapojenými do operace přetažení. Tento příklad vyžaduje, aby formulář obsahoval ovládací prvek RichTextBox a ovládací prvek ListBox a že ovládací prvek ListBox je naplněn seznamem platných názvů souborů. Když uživatel přetáhne název souboru do ovládacího prvku RichTextBox, vyvolá se událost DragEnter ovládacího prvku. V obslužné rutině události je vlastnost EffectDragEventArgs inicializována tak, aby DragDropEffects indikovala, že data odkazovaná cestou k souboru by se měla zkopírovat do ovládacího prvku RichTextBox.

private:
   void Form1_Load( Object^ /*sender*/, EventArgs^ /*e*/ )
   {
      // Sets the AllowDrop property so that data can be dragged onto the control.
      richTextBox1->AllowDrop = true;

      // Add code here to populate the ListBox1 with paths to text files.
   }

   void listBox1_MouseDown( Object^ sender, System::Windows::Forms::MouseEventArgs^ e )
   {
      // Determines which item was selected.
      ListBox^ lb = (dynamic_cast<ListBox^>(sender));
      Point pt = Point(e->X,e->Y);
      int index = lb->IndexFromPoint( pt );

      // Starts a drag-and-drop operation with that item.
      if ( index >= 0 )
      {
         lb->DoDragDrop( lb->Items[ index ], DragDropEffects::Link );
      }
   }

   void richTextBox1_DragEnter( Object^ /*sender*/, DragEventArgs^ e )
   {
      // If the data is text, copy the data to the RichTextBox control.
      if ( e->Data->GetDataPresent( "Text" ) )
            e->Effect = DragDropEffects::Copy;
   }

   void richTextBox1_DragDrop( Object^ /*sender*/, DragEventArgs^ e )
   {
      // Loads the file into the control.
      richTextBox1->LoadFile( dynamic_cast<String^>(e->Data->GetData( "Text" )), System::Windows::Forms::RichTextBoxStreamType::RichText );
   }

private void Form1_Load(object sender, EventArgs e) 
{
   // Sets the AllowDrop property so that data can be dragged onto the control.
   richTextBox1.AllowDrop = true;

   // Add code here to populate the ListBox1 with paths to text files.
}

private void listBox1_MouseDown(object sender, System.Windows.Forms.MouseEventArgs e)
{
   // Determines which item was selected.
   ListBox lb =( (ListBox)sender);
   Point pt = new Point(e.X,e.Y);
   int index = lb.IndexFromPoint(pt);

   // Starts a drag-and-drop operation with that item.
   if(index>=0) 
   {
      lb.DoDragDrop(lb.Items[index].ToString(), DragDropEffects.Link);
   }
}

private void richTextBox1_DragEnter(object sender, DragEventArgs e) 
{
   // If the data is text, copy the data to the RichTextBox control.
   if(e.Data.GetDataPresent("Text"))
      e.Effect = DragDropEffects.Copy;
}

private void richTextBox1_DragDrop(object sender, DragEventArgs e) 
{
   // Loads the file into the control. 
   richTextBox1.LoadFile((String)e.Data.GetData("Text"), System.Windows.Forms.RichTextBoxStreamType.RichText);
}

Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
   ' Sets the AllowDrop property so that data can be dragged onto the control.
   RichTextBox1.AllowDrop = True

   ' Add code here to populate the ListBox1 with paths to text files.

End Sub

Private Sub RichTextBox1_DragEnter(ByVal sender As Object, ByVal e As System.Windows.Forms.DragEventArgs) Handles RichTextBox1.DragEnter
   ' If the data is text, copy the data to the RichTextBox control.
   If (e.Data.GetDataPresent("Text")) Then
      e.Effect = DragDropEffects.Copy
   End If
End Sub


Private Overloads Sub RichTextBox1_DragDrop(ByVal sender As Object, ByVal e As System.Windows.Forms.DragEventArgs) Handles RichTextBox1.DragDrop
   ' Loads the file into the control. 
   RichTextBox1.LoadFile(e.Data.GetData("Text"), System.Windows.Forms.RichTextBoxStreamType.RichText)
End Sub

Private Sub ListBox1_MouseDown(ByVal sender As Object, ByVal e As System.Windows.Forms.MouseEventArgs) Handles ListBox1.MouseDown
   Dim Lb As ListBox
   Dim Pt As New Point(e.X, e.Y)
   Dim Index As Integer

   ' Determines which item was selected.
   Lb = sender
   Index = Lb.IndexFromPoint(Pt)

   ' Starts a drag-and-drop operation with that item.
   If Index >= 0 Then
      Lb.DoDragDrop(Lb.Items(Index), DragDropEffects.Link)
   End If
End Sub

Poznámky

Parametr allowedEffects určuje, ke kterým operacím přetažení může dojít. Pokud operace přetažení potřebuje spolupracovat s aplikacemi v jiném procesu, data by měla být buď základní spravovaná třída (String, Bitmapnebo Metafile), nebo objekt, který implementuje ISerializable nebo IDataObject.

Následující článek popisuje, jak a kdy jsou vyvolány události související s operacemi přetažení myší.

Metoda DoDragDrop určuje ovládací prvek pod aktuálním umístěním kurzoru. Pak zkontroluje, jestli je ovládací prvek platným cílem odstranění.

Pokud je ovládací prvek platným cílem přetažení, je vyvolána událost GiveFeedback se zadaným efektem přetažení. Seznam efektů přetažení najdete v DragDropEffects výčtu.

Změny v poloze kurzoru myši, stavu klávesnice a stavu tlačítka myši jsou sledovány.

• Pokud se uživatel přesune mimo okno, vyvolá se událost DragLeave.

• Pokud myš přejde do jiného ovládacího prvku, DragEnter pro tento ovládací prvek se vyvolá.

• Pokud se myš přesune, ale zůstane ve stejném ovládacím prvku, vyvolá se událost DragOver.

Pokud dojde ke změně stavu klávesnice nebo tlačítka myši, vyvolá se událost QueryContinueDrag a určí, zda má pokračovat přetažením, přetažením dat nebo zrušením operace na základě hodnoty vlastnosti ActionQueryContinueDragEventArgsudálosti .

• Pokud je hodnota DragActionContinue, vyvolá se událost DragOver, aby pokračovala v operaci a událost GiveFeedback je vyvolána s novým efektem, aby bylo možné nastavit odpovídající vizuální zpětnou vazbu. Seznam platných efektů přetažení najdete v DragDropEffects výčtu.

  Poznámka

  Události DragOver a GiveFeedback jsou spárované tak, aby se při přesouvání myši přes cíl přetažení dostal uživatel nejvíce up-to-date feedback na pozici myši.

• Pokud je hodnota DragActionDrop, vrátí se do zdroje hodnota efektu poklesu, takže zdrojová aplikace může provést příslušnou operaci se zdrojovými daty; Například vyjměte data, pokud byla operace přesunutím.

• Pokud je hodnota DragActionCancel, vyvolá se událost DragLeave.

• Výjimka SecurityException

• NullReferenceException

• StackOverflowException

• OutOfMemoryException

• ThreadAbortException

• ExecutionEngineException

• IndexOutOfRangeException

• AccessViolationException

Viz také

• AllowDrop
• DragDrop