DragEnter

Inside Macintosh: OpenDoc Class Reference /: Part 1 - Classes and Methods / ODPart

DragEnter
The DragEnter method should begin tracking a drag operation.
ODDragResult DragEnter (in ODDragItemIterator dragInfo, 
                        in ODFacet facet, 
                        in ODPoint where);
dragInfo
A reference to a drag-item iterator that describes the content, as well as the types and values, of the dragged data.
facet
A reference to a facet where the drag point is located.
where
The location of the drag point, expressed in frame coordinates.
return value
kODTrue if this part accepts drag-and-drop events in its display frame, otherwise kODFalse.

DISCUSSION
OpenDoc calls this method when the drag point has entered the specified facet of this part during a drag operation. Before calling this method, OpenDoc calls the IsDroppable method of the facet's frame to ensure that this part is able to receive a drop.
Your part's DragEnter method should examine the part kinds of the dragged data (using the drag-item iterator specified by the dragInfo parameter), and determine whether it can accept the dragged data. Your part should not at this point attempt to read data from any of the storage units supplied by the drag-item iterator. If your part can accept a drop, it should provide the appropriate feedback to the user, such as displaying its drag border or changing the cursor appearance. If your part cannot handle the part kinds of the dragged data, it should take no action. If your part's DragEnter method returns kODFalse, OpenDoc assumes your part cannot accept a drop. OpenDoc will not make additional calls to your DragWithin or Drop methods as long as the mouse pointer remains in this facet. In addition, if your part calls one of its display frames' SetDroppable method with a value of kODTrue, you must override this method and implement the protocol for drag highlighting and accepting dropped data.

OVERRIDING
When you subclass ODPart, you can override this method. Your override method must not call its inherited method; that is, your override method must implement this method's functionality completely.

EXCEPTIONS

kODErrDoesNotDrop
This part does not support drag and drop.

SEE ALSO
The ODDragResult type (page 922).
The ODPoint type (page 885).
The ODFrame::SetDroppable method (page 333).
The ODPart::DragLeave method (page 502).
The ODPart::DragWithin method (page 503).
The ODPart::Drop method (page 506).
Table 2-1 on page 89 in OpenDoc Programmer's Guide.
"On Entering a Part's Facet" on page 362 in OpenDoc Programmer's Guide.