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NAME
DtDndDropRegister, DtDndVaDropRegister - specify a drop site
SYNOPSIS
#include <Dt/Dnd.h>
void DtDndDropRegister(Widget dropSite,
DtDndProtocol protocols,
unsigned char operations,
XtCallbackList transferCallback,
ArgList argList,
Cardinal argCount);
void DtDndVaDropRegister(Widget dropSite,
DtDndProtocol protocols,
unsigned char operations,
XtCallbackList transferCallback,
...);
DESCRIPTION
The DtDndDropRegister() and DtDndVaDropRegister() functions
register a Motif drop site with import targets based on the
specified data transfer protocols. DtDndDropRegister() may
be called to register a widget as a drop site at any time,
typically soon after the widget is created.
The only difference between DtDndDropRegister() and DtDndVa-
DropRegister() is how the argument list is passed. The
argument list is passed as an ArgList to DtDndDropRegister()
and using VarArgs for DtDndVaDropRegister().
The dropSite argument specifies the widget to register as
the drop site.
The protocol argument specifies the set of data transfer
protocols in which the drop site is able to participate.
Valid values are:
DtDND_TEXT_TRANSFER
The drop site can transfer a list of text.
DtDND_FILENAME_TRANSFER
The drop site can transfer a list of file names.
DtDND_BUFFER_TRANSFER
The drop site can transfer a list of memory
buffers.
A drop site can support any combination of these protocols.
A combination of protocols is specified by the bitwise
inclusive OR of several protocol values.
The operations argument specifies the set of valid opera-
tions associated with a drop site. The operations are:
XmDROP_COPY
Copy operations are valid. The data will be copied
from the drag source.
XmDROP_LINK
Link operations are valid. The data will be linked
using an alternative method.
XmDROP_MOVE
Move operations are valid. The data will be
copied, and optionally deleted, from the drag
source.
A drop site can support any combination of these operations.
A combination of operations is specified by the bitwise
inclusive OR of several operation values.
The transferCallback argument specifies the callback to be
called when the dropped data object has been received by the
drop site. The transferCallback is responsible for
transferring the data from the dropData to the appropriate
internal data structures at the drop site. The arguments
for the convertCallback are the Motif Drag Context, an
XtPointer to application-supplied client data, and an
XtPointer to a DtDndConvertCallbackStruct structure.
The argList argument specifies the optional argument list.
The argCount argument specifies the number of arguments in
argList.
Argument Value Pairs
The DtDndDragStart() and DtDndVaDragStart() functions sup-
port the following optional argument-value pairs. Motif
resources can be set via the argument list as well, provided
they are not resources that are used by the drag and drop
subsystem; see Motif Resources.
DtNregisterChildren (Boolean)
Specifies whether children of a composite drop site
widget should be registered. If True, then the
composite dropSite widget and its children are
registered as a single drop site. If False, then
only the dropSite widget itself is registered as
the drop site. The default is False.
DtNtextIsBuffer (Boolean)
Specifies whether the drops of text selections
should be treated as buffer drops. This attribute
is only valid if protocols includes
DtDND_BUFFER_TRANSFER. If DtNtextIsBuffer is True,
text drops are accepted as unnamed buffers; if it
is False, only drops of the specified protocols are
accepted. The default is False.
DtNpreserveRegistration (Boolean)
Specifies whether to preserve any existing drop
site registration for the dropSite widget. The
application can disable preserving the drop site
registration if the dropSite widget is known not to
be registered as a drop site or that registration
is not desired. This may improve drop site regis-
tration performance. If DtNpreserveRegistration is
True, existing drop site registration is preserved;
if it is False, the existing drop site registration
is replaced. The default is True.
DtNdropAnimateCallback (XtCallbackList)
Specifies the callback to be called when the drop
is complete. This enables graphical animation upon
successful completion of a drop. This callback is
called after the transferCallback is called and
after Motif performs the ``melt'' effect. The
arguments for the DtNDropAnimateCallback are the
Motif Drag Context, an XtPointer to application-
supplied client data, and an XtPointer to a
DtDndDropAnimateCallbackStruct structure. The
Motif Drag Context is in the process of being des-
troyed at this point so the application must not
use it or any of its values in the dropAnimateCall-
back. The default is NULL.
Callbacks
Once the rendezvous with the drag source has been accom-
plished, the application-provided callback functions are
called to perform the data transfer.
First, the transferCallback is called with a reason of
DtCR_DND_TRANSFER_DATA. The application should access the
DtDndContext fields appropriate for the transfer protocol.
The application should parse or type the dropped data to
determine whether it is acceptable. If the dropped data is
not acceptable, the status field of the DtDndTransfer-
CallbackStruct should be set to DtDND_FAILURE.
If the DtNdropAnimateCallback attribute has been specified,
the dropAnimateCallback is then called with a reason of
DtCR_DND_DROP_ANIMATE. The application should perform any
application-provided animations for the drop.
When the transferCallback (or the dropAnimateCallback, if
specified) returns, all memory associated with the drop
transfer is freed. Any data in the callback structures that
will be used after the drop transfer is complete must be
copied by the application.
Callback Information
Each of the callbacks for DtDndDropRegister() and DtDndVa-
DropRegister() has an associated callback structure. These
callbacks cannot be used with the XtAddCallback(3X) inter-
face.
A pointer to the following structure is passed to the
transferCallback:
typedef struct {
int reason;
XEvent *event;
Position x, y;
unsigned char operation;
DtDndContext *dropData;
Boolean completeMove;
DtDndStatus status;
} DtDndTransferCallbackStruct, *DtDndTransferCallback;
The reason argument indicates why the callback was invoked:
DtCR_DND_TRANSFER_DATA.
The event argument is always set to NULL by Motif drag and
drop.
The x and y arguments indicate the coordinates of the
dropped item in relation to the origin of the drop site
widget.
The operation argument indicates the type of drop:
XmDROP_COPY, XmDROP_MOVE or XmDROP_LINK.
The dropData argument contains the data that has been
dropped.
The dragContext argument specifies the ID of the Motif Drag
Context widget associated with this drag and drop transac-
tion.
The completeMove argument indicates whether a move operation
needs to be completed. If the operation is XmDROP_MOVE and
completeMove is set to False in the transferCallback, a
delete does not occur. By default, completeMove is True and
a delete occurs to complete the move operation. The com-
pleteMove field should be set to False if an alternative
method will be used to complete the move.
The status argument indicates the success or failure of the
data transfer. If the data could not be appropriately
moved, copied or linked, the status field must be set to
DtDND_FAILURE. By default, the status field is set to
DtDND_SUCCESS.
A pointer to the following structure is passed to the dro-
pAnimateCallback:
typedef struct {
int reason;
XEvent *event;
Position x, y;
unsigned char operation;
DtDndContext *dropData;
} DtDndDropAnimateCallbackStruct, *DtDndDropAnimateCallback;
The reason argument indicates why the callback was invoked.
The valid reason is DtCR_DND_DROP_ANIMATE.
The event argument is always set to NULL by Motif drag and
drop.
The x and y arguments indicate the coordinates of the
dropped item in relation to the origin of the drop site
widget.
The operation argument indicates the type of drop:
XmDROP_COPY, XmDROP_MOVE or XmDROP_LINK.
The dropData argument contains the data that has been
dropped.
Structures
The following structures are used by the drop site in the
transferCallback to get the transferred data from the drag
and drop subsystem. The DtDndContext structure is passed as
dropData in the DtDndTransferCallbackStruct structure.
typedef struct {
DtDndProtocol protocol;
int numItems;
union {
XmString *strings;
String *files;
DtDndBuffer *buffers;
} data;
} DtDndContext;
The protocol argument indicates the data transfer protocol
under which the data in the DtDndContext is being
transferred. Valid values are:
DtDND_TEXT_TRANSFER
A list of text is being transferred.
DtDND_FILENAME_TRANSFER
A list of file names is being transferred.
DtDND_BUFFER_TRANSFER
A list of memory buffers is being transferred.
The numItems argument indicates the number of items being
transferred.
The data argument is a union containing data that the drop
site should access in the format corresponding to the speci-
fied protocol. The data structures corresponding to the
transfer protocols are as follows.
The strings argument is valid if the protocol is
DtDND_TEXT_TRANSFER. The strings argument is an array of
pointers to Motif strings containing the text being
transferred.
The files argument is valid if the protocol is
DtDND_FILENAME_TRANSFER. It is an array of pointers to the
names of the files being transferred. The file names have
been converted to local host file names where possible.
The buffers argument is valid if the protocol is
DtDND_BUFFER_TRANSFER. It is an array of pointers to
DtDndBuffer structures containing the meory buffers being
transferred.
The following structure is used with
DtDND_FILENAME_TRANSFER:
typedef struct _DtDndBuffer {
void *bp;
int size;
string name;
} DtDndBuffer;
The bp argument points to the buffer data being transferred.
The size argument indicates the number of bytes in the
buffer.
The name argument points to the name of the buffer.
Motif Resources
When it calls XmDropSiteRegister(3X), the DtDndDropRegis-
ter() and DtDndVaDropRegister() functions set Motif
resources; the application must not modify the values of any
of these resources. Resources other than those listed here
can be used and are passed through to the underlying
XmDropRegister(). call.
The following resources are modified by DtDndDropRegister()
and DtDndVaDropRegister() in the Motif Drag Context.
XmNdestroyCallback
XmNdropTransfers
XmNnumDropTransfers
XmNtransferProc
XmNtransferStatus
The following resources are modified by DtDndDropRegister()
and DtDndVaDropRegister() in the Motif Drop Site.
XmNdropProc
XmNdropSiteOperations
XmNdropSiteType
XmNimportTargets
XmNnumImportTargets
RETURN VALUE
The DtDndDropRegister() and DtDndVaDropRegister() functions
return no value.
SEE ALSO
DtDnd(5), DtDtsDataTypeToAttributeValue(3), DtDndDrag-
Start(3), DtDndVaDragStart(3), DtDndDropUnregister(3),
XmDragContext(3X), XmDropSite(3X), XmDropSiteRegister(3X),
XmDropSiteUpdate(3X), XmDropTransfer(3X),
XmDropTransferStart(3X).
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