Tk_CreateSelHandler(3Tk)Tk_CreateSelHandler(3Tk)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
isn't 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.
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Tk_CreateSelHandler(3Tk)Tk_CreateSelHandler(3Tk)
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. |
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Tk_CreateSelHandler(3Tk)Tk_CreateSelHandler(3Tk)
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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