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Error(3)		       User Contributed Perl Documentation			 Error(3)

       Tk::Error - Method invoked to process background errors


	   require Tk::ErrorDialog;


	   sub Tk::Error
	     my ($widget,$error,@locations) = @_;


       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

       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

       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

       The Tk module includes a default Tk::Error subroutine that simply reports the error on

       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.

       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.

       Tk::bind Tk::after Tk::fileevent

       background error, reporting

perl v5.16.3				    2014-06-10					 Error(3)
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