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 for-mat format
mat 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 selection
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 Con-ventions Conventions
ventions Manual (ICCCM) or any other form in which an application is willing to present the selec-tion. selection.
tion. 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 thou-sand thousand
sand 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 argu-ment argument
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 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)
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