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.so man.macros

.TH Tk_CreateSelHandler 3 4.0 Tk "Tk Library Procedures"

.BS

.SH NAME

Tk_CreateSelHandler, Tk_DeleteSelHandler \- arrange to handle requests for a selection

.SH SYNOPSIS

.nf

\fB#include \fR

.sp

\fBTk_CreateSelHandler\fR(\fItkwin, selection, target, proc, clientData, format\fR)

.sp

\fBTk_DeleteSelHandler\fR(\fItkwin, selection, target\fR)

.SH ARGUMENTS

.AS Tk_SelectionProc clientData

.AP Tk_Window tkwin in

Window for which \fIproc\fR will provide selection information.

.AP Atom selection in

The name of the selection for which \fIproc\fR will provide

selection information.

.AP Atom target in

Form in which \fIproc\fR can provide the selection (e.g. STRING

or FILE_NAME).  Corresponds to \fItype\fR arguments in \fBselection\fR

commands.

.AP Tk_SelectionProc *proc in

Procedure to invoke whenever the selection is owned by \fItkwin\fR

and the selection contents are requested in the format given by

\fItarget\fR.

.AP ClientData clientData in

Arbitrary one-word value to pass to \fIproc\fR.

.AP Atom format in

If the selection requestor isn't in this process, \fIformat\fR determines

the representation used to transmit the selection to its

requestor.

.BE

.SH DESCRIPTION

.PP

\fBTk_CreateSelHandler\fR arranges for a particular procedure

(\fIproc\fR) to be called whenever \fIselection\fR is owned by

\fItkwin\fR and the selection contents are requested in the

form given by \fItarget\fR.

\fITarget\fR 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.

.PP

\fIProc\fR should have arguments and result that match the

type \fBTk_SelectionProc\fR:

.CS

typedef int Tk_SelectionProc(

        ClientData \fIclientData\fR,

        int \fIoffset\fR,

        char *\fIbuffer\fR,

        int \fImaxBytes\fR);

.CE

The \fIclientData\fR parameter to \fIproc\fR is a copy of the

\fIclientData\fR argument given to \fBTk_CreateSelHandler\fR.

Typically, \fIclientData\fR points to a data

structure containing application-specific information that is

needed to retrieve the selection.  \fIOffset\fR specifies an

offset position into the selection, \fIbuffer\fR specifies a

location at which to copy information about the selection, and

\fImaxBytes\fR specifies the amount of space available at

\fIbuffer\fR.  \fIProc\fR should place a NULL-terminated string

at \fIbuffer\fR containing \fImaxBytes\fR or fewer characters

(not including the terminating NULL), and it should return a

count of the number of non-NULL characters stored at

\fIbuffer\fR.  If the selection no longer exists (e.g. it once

existed but the user deleted the range of characters containing

it), then \fIproc\fR should return -1.

.PP

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 \fIproc\fR

one or more times, using successively higher values of \fIoffset\fR

to retrieve successive portions of the selection.  If \fIproc\fR

returns a count less than \fImaxBytes\fR it means that the entire

remainder of the selection has been returned.  If \fIproc\fR's return

value is \fImaxBytes\fR it means there may be additional information

in the selection, so Tk must make another call to \fIproc\fR to

retrieve the next portion.

.PP

\fIProc\fR 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 \fIformat\fR argument to

\fBTk_CreateSelHandler\fR 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 \fIformat\fR is not

STRING, then Tk will take the value returned by \fIproc\fR and divided

it into fields separated by white space.  If \fIformat\fR is ATOM,

then Tk will return the selection as an array of atoms, with each

field in \fIproc\fR's result treated as the name of one atom.  For

any other value of \fIformat\fR, Tk will return the selection as an

array of 32-bit values where each field of \fIproc\fR's result is

treated as a number and translated to a 32-bit value.  In any event,

the \fIformat\fR atom is returned to the selection requestor along

with the contents of the selection.

.PP

If \fBTk_CreateSelHandler\fR is called when there already exists a

handler for \fIselection\fR and \fItarget\fR on \fItkwin\fR, then the

existing handler is replaced with a new one.

.PP

\fBTk_DeleteSelHandler\fR removes the handler given by \fItkwin\fR,

\fIselection\fR, and \fItarget\fR, if such a handler exists.

If there is no such handler then it has no effect.

.SH KEYWORDS

format, handler, selection, target