|
IDropTarget::DragEnter
Indicates whether or not a drop can be accepted and the drop's effect if
accepted.
HRESULT DragEnter(
IDataObject * pDataObject,
| //IDataObject interface for the source data
| DWORD grfKeyState,
| //Current state of keyboard modifier keys
| POINTL pt,
| //Current cursor coordinates
| DWORD * pdwEffect
| //Effect of the drag-and-drop operation
| );
|
|
Parameters
pDataObject
[in] Points to the data object being transferred in the drag-and-drop
operation. The data is represented in the IDataObject interface. If the drop occurs, this data object will be incorporated into the
target.
grfKeyState
[in] Identifies the current state of the keyboard modifier keys on the
keyboard. Valid values can be a combination of any of the flags MK_CONTROL, MK_SHIFT,
MK_ALT, MK_BUTTON, MK_LBUTTON, MK_MBUTTON, and MK_RBUTTON.
pt
[in] Points to the current cursor coordinates in the coordinate space of the
drop target window.
pdwEffect
[in, out] Specifies the current effect flag. Valid values are from the DROPEFFECT enumeration.
Return Values
S_OK
The function completed its task successfully.
E_OUTOFMEMORY
Out of memory.
E_INVALIDARG
One or more arguments are invalid.
E_UNEXPECTED
An unexpected error occurred.
Comments
The DoDragDrop function calls this method the first time the user drags the mouse into the
registered window of a drop target.
In the IDropTarget::DragEnter method, you must determine the effect of dropping the data on the target by
examining the formats and medium specified for the data object along with the
state of the modifier keys. The following modifier keys affect the result of the
drop:
Key Combination
| User-Visible Feedback
| Drop Effect
| CTRL + SHIFT
| =
| DROPEFFECT_LINK
| CTRL
| +
| DROPEFFECT_COPY
| No keys or SHIFT
| None
| DROPEFFECT_MOVE
|
You communicate the effect of the drop back to the source through DoDragDrop in the pdwEffect parameter. The DoDragDrop function then calls IDropSource::GiveFeedback so that the source application can display the appropriate visual feedback to
the user.
On entry to IDropTarget::DragEnter, the pdwEffect parameter is set to the effects given to the DoDragDrop function. The IDropTarget::DragEnter method must choose one of these effects or disable the drop.
Upon return, pdwEffect is set to either DROPEFFECT_COPY to copy the dragged data to the target,
DROPEFFECT_LINK to create a link to the source data, or DROPEFFECT_MOVE to allow
the dragged data to be permanently moved from the source application to the
target.
You may also wish to provide appropriate visual feedback in the target window.
See Also
DoDragDrop, IDropSource, IDropTarget, RegisterDragDrop, RevokeDragDrop
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