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
information.

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
commands.

Tk_SelectionProc *proc (in) Procedure to invoke
whenever the selection is
owned by tkwin and the
selection contents 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
is not 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, 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 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 additional 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 argument 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 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)