.\" Automatically generated by Pod::Man 4.10 (Pod::Simple 3.35)
.\"
.\" Standard preamble:
.\" ========================================================================
.de Sp \" Vertical space (when we can't use .PP)
.if t .sp .5v
.if n .sp
..
.de Vb \" Begin verbatim text
.ft CW
.nf
.ne \\$1
..
.de Ve \" End verbatim text
.ft R
.fi
..
.\" Set up some character translations and predefined strings.  \*(-- will
.\" give an unbreakable dash, \*(PI will give pi, \*(L" will give a left
.\" double quote, and \*(R" will give a right double quote.  \*(C+ will
.\" give a nicer C++.  Capital omega is used to do unbreakable dashes and
.\" therefore won't be available.  \*(C` and \*(C' expand to `' in nroff,
.\" nothing in troff, for use with C<>.
.tr \(*W-
.ds C+ C\v'-.1v'\h'-1p'\s-2+\h'-1p'+\s0\v'.1v'\h'-1p'
.ie n \{\
.    ds -- \(*W-
.    ds PI pi
.    if (\n(.H=4u)&(1m=24u) .ds -- \(*W\h'-12u'\(*W\h'-12u'-\" diablo 10 pitch
.    if (\n(.H=4u)&(1m=20u) .ds -- \(*W\h'-12u'\(*W\h'-8u'-\"  diablo 12 pitch
.    ds L" ""
.    ds R" ""
.    ds C` ""
.    ds C' ""
'br\}
.el\{\
.    ds -- \|\(em\|
.    ds PI \(*p
.    ds L" ``
.    ds R" ''
.    ds C`
.    ds C'
'br\}
.\"
.\" Escape single quotes in literal strings from groff's Unicode transform.
.ie \n(.g .ds Aq \(aq
.el       .ds Aq '
.\"
.\" If the F register is >0, we'll generate index entries on stderr for
.\" titles (.TH), headers (.SH), subsections (.SS), items (.Ip), and index
.\" entries marked with X<> in POD.  Of course, you'll have to process the
.\" output yourself in some meaningful fashion.
.\"
.\" Avoid warning from groff about undefined register 'F'.
.de IX
..
.nr rF 0
.if \n(.g .if rF .nr rF 1
.if (\n(rF:(\n(.g==0)) \{\
.    if \nF \{\
.        de IX
.        tm Index:\\$1\t\\n%\t"\\$2"
..
.        if !\nF==2 \{\
.            nr % 0
.            nr F 2
.        \}
.    \}
.\}
.rr rF
.\" ========================================================================
.\"
.IX Title "Error 3pm"
.TH Error 3pm "2018-11-01" "perl v5.28.0" "User Contributed Perl Documentation"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
.if n .ad l
.nh
.SH "NAME"
Tk::Error \- Method invoked to process background errors
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
Customization:
.PP
.Vb 1
\&    require Tk::ErrorDialog;
.Ve
.PP
or
.PP
.Vb 4
\&    sub Tk::Error
\&    {
\&      my ($widget,$error,@locations) = @_;
\&      ...
\&
\&    }
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
The \fBTk::Error\fR method is invoked by perl/Tk when a background
error occurs. Two possible implementations are provided in the
distribution and individual applications or users can (re)define a \fBTk::Error\fR
method (e.g. as a perl sub) if they wish to handle background
errors in some other manner.
.PP
A background error is one that occurs in a command that didn't
originate with the application.  For example, if an error occurs
while executing a callback specified with a
bind or a after
command, then it is a background error.  For a non-background error,
the error can simply be returned up through nested subroutines
until it reaches the top-level code in the application;
then the application can report the error in whatever way it
wishes.  When a background error occurs, the unwinding ends in
the Tk library and there is no obvious way for Tk to report
the error.
.PP
When Tk detects a background error, it saves information about the
error and invokes the \fBTk::Error\fR method later when Tk is idle.
.PP
\&\fBTk::Error\fR is invoked by perl/Tk as if by the perl code:
.PP
    \fI\f(CI$mainwindow\fI\fR\->\fBTk::Error\fR(\fI\*(L"error message\*(R"\fR, \fIlocation ...\fR);
.PP
\&\fI\f(CI$mainwindow\fI\fR is the \fBMainWindow\fR associated with widget which
detected the error, \fI\*(L"error message\*(R"\fR is a string describing the error
that has been detected, \fIlocation\fR is a list of one or more \*(L"locations\*(R"
which describe the call sequence at the point the error was detected.
.PP
The locations are a typically a mixture of perl location reports giving
script name and line number, and simple strings describing locations in
core Tk or perl/Tk C code.
.PP
Tk will ignore any result returned by the \fBTk::Error\fR method.
If another error occurs within the \fBTk::Error\fR method
(for example if it calls \fBdie\fR) then Tk reports this error
itself by writing a message to stderr (this is to avoid infinite loops
due to any bugs in \fBTk::Error\fR).
.PP
If several background errors accumulate before \fBTk::Error\fR
is invoked to process them, \fBTk::Error\fR will be invoked once
for each error, in the order they occurred.
However, if \fBTk::Error\fR calls \fBTk\->break\fR, then
any remaining errors are skipped without calling \fBTk::Error\fR.
.PP
The \fBTk\fR module includes a default \fBTk::Error\fR subroutine
that simply reports the error on stderr.
.SH "Tk::ErrorDialog"
.IX Header "Tk::ErrorDialog"
An alternate definition is provided via:
.PP
    \f(CW\*(C`require Tk::ErrorDialog;\*(C'\fR
.PP
that posts a dialog box containing the error message and offers
the user a chance to see a stack trace showing where the
error occurred.
.PP
This is an \s-1OO\s0 implementation of the Tcl/Tk command \fBbgerror\fR, with a
twist: since there is only one \fBErrorDialog\fR widget, you aren't required
to invoke the constructor to create it; it will be created
automatically when the first background error occurs.  However, in
order to configure the \fI\-cleanupcode\fR and \fI\-appendtraceback\fR
\&\fBErrorDialog\fR options you must call the constructor and create it
manually.
.PP
The \fBErrorDialog\fR object essentially consists of two subwidgets: a
\&\fBDialog\fR widget to display the background error and a \fBText\fR widget
for the traceback information.  If required, you can invoke various
widget methods to customize these subwidgets \- their advertised names
are described below.
.PP
    \fI\f(CI$mw\fI\fR\->\fBErrorDialog\fR(\-cleanupcode => \fIcode\fR, \-appendtraceback => \fIbool\fR);
.PP
\&\f(CW$mw\fR is a window reference.
.PP
\&\fIcode\fR is a \s-1CODE\s0 reference if special post-background error
processing is required (default is undefined). The callback subroutine
is called with \f(CW@_\fR having the same arguments that \fBTk::Error\fR was
invoked with.
.PP
\&\fIbool\fR is a boolean indicating whether or not to append successive
tracebacks (default is 1, do append).
.SS "Advertised ErrorDialog widgets"
.IX Subsection "Advertised ErrorDialog widgets"
\&\fIerror_dialog\fR is the Dialog widget reference.
.PP
\&\fItext\fR is the Text widget reference containing the traceback information.
.SH "BUGS"
.IX Header "BUGS"
If \fBafter\fR or \fBfileevent\fR are not invoked as methods of a widget
then perl/Tk is unable to provide a \fI\f(CI$mainwindow\fI\fR argument.
To support such code from earlier versions of perl/Tk
perl/Tk therefore calls \fBTk::Error\fR with string 'Tk' instead:
\&\fBTk\->Tk::Error\e(...\e)\fR.
In this case the \fBTk::Error\fR in \fBTk::ErrorDialog\fR and similar
implementations cannot \*(L"popup\*(R" a window as they don't know which display
to use.  A mechanism to supply \fIthe\fR \fBMainWindow\fR in applications
which only have one (a very common case) should be provided.
.SH "SEE ALSO"
.IX Header "SEE ALSO"
Tk::bind
Tk::after
Tk::fileevent
.SH "KEYWORDS"
.IX Header "KEYWORDS"
background error, reporting