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QueryContinueDragEventHandler Delegate

Represents the method that will handle the QueryContinueDrag event of a Control.

[Visual Basic]
<Serializable>
Public Delegate Sub QueryContinueDragEventHandler( _
   ByVal sender As Object, _
   ByVal e As QueryContinueDragEventArgs _
)
[C#]
[Serializable]
public delegate void QueryContinueDragEventHandler(
   object sender,
   QueryContinueDragEventArgs e
);
[C++]
[Serializable]
public __gc __delegate void QueryContinueDragEventHandler(
   Object* sender,
   QueryContinueDragEventArgs* e
);

[JScript] In JScript, you can use the delegates in the .NET Framework, but you cannot define your own.

Parameters [Visual Basic, C#, C++]

The declaration of your event handler must have the same parameters as the QueryContinueDragEventHandler delegate declaration.

sender
The source of an event.
e
A QueryContinueDragEventArgs that contains the event data.

Remarks

When you create a QueryContinueDragEventHandler 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 handling events with delegates, see Events and Delegates.

Example

[Visual Basic, C#, C++] The following example demonstrates a drag-and-drop operation between two ListBox controls. The example calls the DoDragDrop method when the drag action starts. The drag action starts if the mouse has moved more than SystemInformation.DragSize from the mouse location during the MouseDown event. The IndexFromPoint method is used to determine the index of the item to drag during the MouseDown event.

[Visual Basic, C#, C++] The example also demonstrates using custom cursors for the drag-and-drop operation. The example assumes that two cursor files, 3dwarro.cur and 3dwno.cur, exist in the application directory, for the custom drag and no-drop cursors, respectively. The custom cursors will be used if the UseCustomCursorsCheck CheckBox is checked. The custom cursors are set in the GiveFeedback event handler.

[Visual Basic, C#, C++] The keyboard state is evaluated in the DragOver event handler for the right ListBox, to determine what the drag operation will be based upon state of the SHIFT, CTRL, ALT, or CTRL+ALT keys. The location in the ListBox where the drop would occur is also determined during the DragOver event. If the data to drop is not a String, then the DragEventArgs.Effect is set to DragDropEffects.None. Finally, the status of the drop is displayed in the DropLocationLabel Label.

[Visual Basic, C#, C++] The data to drop for the right ListBox is determined in the DragDrop event handler and the String value is added at the appropriate place in the ListBox. If the drag operation moves outside the bounds of the form, then the drag-and-drop operation is canceled in the QueryContinueDrag event handler.

[Visual Basic, C#, C++] This code excerpt demonstrates using the QueryContinueDragEventHandler delegate with the QueryContinueDrag event. See the DoDragDrop method for the complete code example.

[Visual Basic] 
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, System.Windows.Forms.ListBox)

    If Not (lb is 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

[C#] 
private void ListDragSource_QueryContinueDrag(object sender, System.Windows.Forms.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;
        }
    }
}

[C++] 
private:
   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 != 0) {

            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;
            }
         }
      }

[JScript] No example is available for JScript. To view a Visual Basic, C#, or C++ example, click the Language Filter button Language Filter in the upper-left corner of the page.

Requirements

Namespace: System.Windows.Forms

Platforms: Windows 98, Windows NT 4.0, Windows Millennium Edition, Windows 2000, Windows XP Home Edition, Windows XP Professional, Windows Server 2003 family

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

See Also

System.Windows.Forms Namespace | OnQueryContinueDrag | QueryContinueDrag | QueryContinueDragEventArgs

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