COleDropSource Class

Allows data to be dragged to a drop target.

Syntax

class COleDropSource : public CCmdTarget

Members

Public Constructors

Public Methods

Remarks

The COleDropTarget class handles the receiving portion of the drag-and-drop operation. The COleDropSource object is responsible for determining when a drag operation begins, providing feedback during the drag operation, and determining when the drag operation ends.

To use a COleDropSource object, just call the constructor. This simplifies the process of determining what events, such as a mouse click, begin a drag operation using COleDataSource::DoDragDrop, COleClientItem::DoDragDrop, or COleServerItem::DoDragDrop function. These functions will create a COleDropSource object for you. You might want to modify the default behavior of the COleDropSource overridable functions. These member functions will be called at the appropriate times by the framework.

For more information on drag-and-drop operations using OLE, see the article OLE drag and drop.

For more information, see IDropSource in the Windows SDK.

Inheritance Hierarchy

CObject

CCmdTarget

COleDropSource

Requirements

Header: afxole.h

COleDropSource::COleDropSource

Constructs a COleDropSource object.

COleDropSource();

COleDropSource::GiveFeedback

Called by the framework after calling COleDropTarget::OnDragOver or COleDropTarget::DragEnter.

virtual SCODE GiveFeedback(DROPEFFECT dropEffect);

Parameters

dropEffect
The effect you would like to display to the user, usually indicating what would happen if a drop occurred at this point with the selected data. Typically, this is the value returned by the most recent call to CView::OnDragEnter or CView::OnDragOver. It can be one or more of the following:

• DROPEFFECT_NONE A drop would not be allowed.

• DROPEFFECT_COPY A copy operation would be performed.

• DROPEFFECT_MOVE A move operation would be performed.

• DROPEFFECT_LINK A link from the dropped data to the original data would be established.

• DROPEFFECT_SCROLL A drag scroll operation is about to occur or is occurring in the target.

Return Value

Returns DRAGDROP_S_USEDEFAULTCURSORS if dragging is in progress, NOERROR if it is not.

Remarks

Override this function to provide feedback to the user about what would happen if a drop occurred at this point. The default implementation uses the OLE default cursors. For more information on drag-and-drop operations using OLE, see the article OLE drag and drop.

For more information, see IDropSource::GiveFeedback, IDropTarget::DragOver, and IDropTarget::DragEnter in the Windows SDK.

COleDropSource::OnBeginDrag

Called by the framework when an event occurs that could begin a drag operation, such as pressing the left mouse button.

virtual BOOL OnBeginDrag(CWnd* pWnd);

Parameters

pWnd
Points to the window that contains the selected data.

Return Value

Nonzero if dragging is allowed, otherwise 0.

Remarks

Override this function if you want to modify the way the dragging process is started. The default implementation captures the mouse and stays in drag mode until the user clicks the left or right mouse button or hits ESC, at which time it releases the mouse.

COleDropSource::QueryContinueDrag

After dragging has begun, this function is called repeatedly by the framework until the drag operation is either canceled or completed.

virtual SCODE QueryContinueDrag(
    BOOL bEscapePressed,
    DWORD dwKeyState);

Parameters

bEscapePressed
States whether the ESC key has been pressed since the last call to COleDropSource::QueryContinueDrag.

dwKeyState
Contains the state of the modifier keys on the keyboard. This is a combination of any number of the following: MK_CONTROL, MK_SHIFT, MK_ALT, MK_LBUTTON, MK_MBUTTON, and MK_RBUTTON.

Return Value

DRAGDROP_S_CANCEL if the ESC key or right button is pressed, or left button is raised before dragging starts. DRAGDROP_S_DROP if a drop operation should occur. Otherwise S_OK.

Remarks

Override this function if you want to change the point at which dragging is canceled or a drop occurs.

The default implementation initiates the drop or cancels the drag as follows. It cancels a drag operation when the ESC key or the right mouse button is pressed. It initiates a drop operation when the left mouse button is raised after dragging has started. Otherwise, it returns S_OK and performs no further operations.

Because this function is called frequently, it should be optimized as much as possible.

See also

MFC Sample HIERSVR
MFC Sample OCLIENT
CCmdTarget Class
Hierarchy Chart