Error(3) User Contributed Perl Documentation Error(3)NAMETk::Error - Method invoked to process background errors
SYNOPSIS
Customization:
require Tk::ErrorDialog;
or
sub Tk::Error
{
my ($widget,$error,@locations) = @_;
...
}
DESCRIPTION
The Tk::Error 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 Tk::Error method
(e.g. as a perl sub) if they wish to handle background errors in some
other manner.
A background error is one that occurs in a command that didn't origi‐
nate with the application. For example, if an error occurs while exe‐
cuting 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.
When Tk detects a background error, it saves information about the
error and invokes the Tk::Error method later when Tk is idle.
Tk::Error is invoked by perl/Tk as if by the perl code:
$mainwindow->Tk::Error("error message", location ...);
$mainwindow is the MainWindow associated with widget which detected the
error, "error message" is a string describing the error that has been
detected, location is a list of one or more "locations" which describe
the call sequence at the point the error was detected.
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.
Tk will ignore any result returned by the Tk::Error method. If another
error occurs within the Tk::Error method (for example if it calls die)
then Tk reports this error itself by writing a message to stderr (this
is to avoid infinite loops due to any bugs in Tk::Error).
If several background errors accumulate before Tk::Error is invoked to
process them, Tk::Error will be invoked once for each error, in the
order they occurred. However, if Tk::Error calls Tk->break, then any
remaining errors are skipped without calling Tk::Error.
The Tk module includes a default Tk::Error subroutine that simply
reports the error on stderr.
Tk::ErrorDialog
An alternate definition is provided via:
"require Tk::ErrorDialog;"
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.
This is an OO implementation of the Tcl/Tk command bgerror, with a
twist: since there is only one ErrorDialog widget, you aren't required
to invoke the constructor to create it; it will be created automati‐
cally when the first background error occurs. However, in order to
configure the -cleanupcode and -appendtraceback ErrorDialog options you
must call the constructor and create it manually.
The ErrorDialog object essentially consists of two subwidgets: a Dialog
widget to display the background error and a Text widget for the trace‐
back information. If required, you can invoke various widget methods
to customize these subwidgets - their advertised names are described
below.
$mw->ErrorDialog(-cleanupcode => code, -appendtraceback => bool);
$mw is a window reference.
code is a CODE reference if special post-background error processing is
required (default is undefined). The callback subroutine is called with
@_ having the same arguments that Tk::Error was invoked with.
bool is a boolean indicating whether or not to append successive trace‐
backs (default is 1, do append).
Advertised ErrorDialog widgets
error_dialog is the Dialog widget reference.
text is the Text widget reference containing the traceback information.
BUGS
If after or fileevent are not invoked as methods of a widget then
perl/Tk is unable to provide a $mainwindow argument. To support such
code from earlier versions of perl/Tk perl/Tk therefore calls Tk::Error
with string 'Tk' instead: Tk->Tk::Error\(...\). In this case the
Tk::Error in Tk::ErrorDialog and similar implementations cannot "popup"
a window as they don't know which display to use. A mechanism to sup‐
ply the MainWindow in applications which only have one (a very common
case) should be provided.
SEE ALSO
Tk::bind Tk::after Tk::fileevent
KEYWORDS
background error, reporting
perl v5.8.8 2004-02-28 Error(3)
