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NAME
Tk_CreateSelHandler, Tk_DeleteSelHandler - arrange to handle
requests for a selection
SYNOPSIS
#include <tk.h>
Tk_CreateSelHandler(tkwin, selection, target, proc, clientData, format)
Tk_DeleteSelHandler(tkwin, selection, target)
ARGUMENTS
Tk_Window tkwin (in) Window for which
proc will provide
selection informa-
tion.
Atom selection (in) The name of the
selection for
which proc will
provide selection
information.
Atom target (in) Form in which proc
can provide the
selection (e.g.
STRING or
FILE_NAME).
Corresponds to
type arguments in
selection com-
mands.
Tk_SelectionProc *proc (in) Procedure to
invoke whenever
the selection is
owned by tkwin and
the selection con-
tents are
requested in the
format given by
target.
ClientData clientData (in) Arbitrary one-word
value to pass to
proc.
Atom format (in) If the selection
requestor isn't in
this process,
format determines
the representation
used to transmit
the selection to
its requestor.
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DESCRIPTION
Tk_CreateSelHandler arranges for a particular procedure
(proc) to be called whenever selection is owned by tkwin and
the selection contents are requested in the form given by
target. Target should be one of the entries defined in the
left column of Table 2 of the X Inter-Client Communication
Conventions Manual (ICCCM) or any other form in which an
application is willing to present the selection. The most
common form is STRING.
Proc should have arguments and result that match the type
Tk_SelectionProc:
typedef int Tk_SelectionProc(
ClientData clientData,
int offset,
char *buffer,
int maxBytes);
The clientData parameter to proc is a copy of the clientData
argument given to Tk_CreateSelHandler. Typically, client-
Data points to a data structure containing application-
specific information that is needed to retrieve the selec-
tion. Offset specifies an offset position into the selec-
tion, buffer specifies a location at which to copy informa-
tion about the selection, and maxBytes specifies the amount
of space available at buffer. Proc should place a NULL-
terminated string at buffer containing maxBytes or fewer
characters (not including the terminating NULL), and it
should return a count of the number of non-NULL characters
stored at buffer. If the selection no longer exists (e.g.
it once existed but the user deleted the range of characters
containing it), then proc should return -1.
When transferring large selections, Tk will break them up
into smaller pieces (typically a few thousand bytes each)
for more efficient transmission. It will do this by calling
proc one or more times, using successively higher values of
offset to retrieve successive portions of the selection. If
proc returns a count less than maxBytes it means that the
entire remainder of the selection has been returned. If
proc's return value is maxBytes it means there may be addi-
tional information in the selection, so Tk must make another
call to proc to retrieve the next portion.
Proc always returns selection information in the form of a
character string. However, the ICCCM allows for information
to be transmitted from the selection owner to the selection
requestor in any of several formats, such as a string, an
array of atoms, an array of integers, etc. The format argu-
ment to Tk_CreateSelHandler indicates what format should be
used to transmit the selection to its requestor (see the
middle column of Table 2 of the ICCCM for examples). If
format is not STRING, then Tk will take the value returned
by proc and divided it into fields separated by white space.
If format is ATOM, then Tk will return the selection as an
array of atoms, with each field in proc's result treated as
the name of one atom. For any other value of format, Tk
will return the selection as an array of 32-bit values where
each field of proc's result is treated as a number and
translated to a 32-bit value. In any event, the format atom
is returned to the selection requestor along with the con-
tents of the selection.
If Tk_CreateSelHandler is called when there already exists a
handler for selection and target on tkwin, then the existing
handler is replaced with a new one.
Tk_DeleteSelHandler removes the handler given by tkwin,
selection, and target, if such a handler exists. If there
is no such handler then it has no effect.
KEYWORDS
format, handler, selection, target
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