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).

   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 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