Occurs during a drag operation.
Assembly: System.Windows.Forms (in System.Windows.Forms.dll)
The event is raised when a drag-and-drop operation is started. With the event, the source of a drag event can modify the appearance of the mouse pointer in order to give the user visual feedback during a drag-and-drop operation.
The following describes how and when events related to drag-and-drop operations are raised.
The DoDragDrop method determines the control under the current cursor location. It then checks to see if the control is a valid drop target.
If the control is a valid drop target, the event is raised with the drag-and-drop effect specified. For a list of drag-and-drop effects, see the DragDropEffects enumeration.
Changes in the mouse cursor position, keyboard state, and mouse button state are tracked.
If the user moves out of a window, the DragLeave event is raised.
If the mouse enters another control, the DragEnter for that control is raised.
If the mouse moves but stays within the same control, the DragOver event is raised.
If there is a change in the keyboard or mouse button state, the QueryContinueDrag event is raised and determines whether to continue the drag, to drop the data, or to cancel the operation based on the value of the Action property of the event's QueryContinueDragEventArgs.
If the value of DragAction is Continue, the DragOver event is raised to continue the operation and the event is raised with the new effect so appropriate visual feedback can be set. For a list of valid drop effects, see the DragDropEffects enumeration.
The DragOver and events are paired so that as the mouse moves across the drop target, the user is given the most up-to-date feedback on the mouse's position.
If the value of DragAction is Drop, the drop effect value is returned to the source, so the source application can perform the appropriate operation on the source data; for example, cut the data if the operation was a move.
For more information about handling events, see Handling and Raising Events.
The following code 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 requires 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 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 on 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 None in DragDropEffects. 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.
This code excerpt demonstrates using the event. See the DoDragDrop method for the complete code example.
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