Tk_CreateSelHandler(3) Tk Library Procedures Tk_CreateSelHandler(3)
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
Window for which proc will provide selection information. The name of
the selection for which proc will provide selection information. Form
in which proc can provide the selection (e.g. STRING or FILE_NAME).
Corresponds to type arguments in selection commands. Procedure to
invoke whenever the selection is owned by tkwin and the selection con-
tents are requested in the format given by target. Arbitrary one-word
value to pass to proc. If the selection requestor is not in this
process, format determines the representation used to transmit the
selection to its requestor.
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, client-
Data points to a data structure containing application-specific infor-
mation 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-ter-
minated 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 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)
CrtSelHdlr 8.5.4 - Generated Sat Aug 23 08:06:29 CDT 2008