CrtSelHdlr
Tk_CreateSelHandler(3) Tk Library Procedures Tk_CreateSelHandler(3)
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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 pro-
vide the selection (e.g.
STRING or FILE_NAME). Corre-
sponds to type arguments in
selection commands.
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 selec-
tion 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_Selection-
Proc:
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, clientData points to a data
structure containing application-specific information that is needed to
retrieve the selection. Offset specifies an offset position into the
selection, buffer specifies a location at which to copy information
about the selection, and maxBytes specifies the amount of space avail-
able 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 charac-
ters 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 trans-
mission. It will do this by calling proc one or more times, using suc-
cessively 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 additional infor-
mation 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 argument to Tk_CreateSelHandler indicates what format
should be used to transmit the selection to its requestor (see the mid-
dle 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 selec-
tion requestor along with the contents 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
Tk 4.0 Tk_CreateSelHandler(3)
