Assembly: System.Windows.Forms (in System.Windows.Forms.dll)
'Declaration Public Delegate Sub QueryContinueDragEventHandler ( _ sender As Object, _ e As QueryContinueDragEventArgs _ )
When you create a 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.
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.
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.
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.
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.
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 (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
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