NAME¶
Tk::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 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.
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 automatically 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 traceback 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
tracebacks (default is 1, do append).
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 supply
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