Occurs when an object is dragged over the control's bounds.
Assembly: System.Windows.Forms (in System.Windows.Forms.dll)
Theevent is raised when the mouse cursor moves within the bounds of the control 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.
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, theevent is raised.
If there is a change in the keyboard or mouse button state, theQueryContinueDrag 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 value is Continue, the event is raised to continue the operation and the GiveFeedback 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 GiveFeedback 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.and
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 UseCustomCursorsCheckCheckBox is checked. The custom cursors are set in the GiveFeedback event handler.
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 DoDragDrop method for the complete code example.event. See the
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 = CTL + 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 ' CTL 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
Available since 1.1