1Error(3) User Contributed Perl Documentation Error(3)
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6 Tk::Error - Method invoked to process background errors
7
9 Customization:
10 require Tk::ErrorDialog;
12 or
14 sub Tk::Error
16 {
17 my ($widget,$error,@locations) = @_;
18 ...
19 }
21
23 The Tk::Error method is invoked by perl/Tk when a background error
24 occurs. Two possible implementations are provided in the distribution
25 and individual applications or users can (re)define a Tk::Error method
26 (e.g. as a perl sub) if they wish to handle background errors in some
27 other manner.
28 A background error is one that occurs in a command that didn't
30 originate with the application. For example, if an error occurs while
31 executing a callback specified with a bind or a after command, then it
32 is a background error. For a non-background error, the error can
33 simply be returned up through nested subroutines until it reaches the
34 top-level code in the application; then the application can report the
35 error in whatever way it wishes. When a background error occurs, the
36 unwinding ends in the Tk library and there is no obvious way for Tk to
37 report the error.
38 When Tk detects a background error, it saves information about the
40 error and invokes the Tk::Error method later when Tk is idle.
41 Tk::Error is invoked by perl/Tk as if by the perl code:
43 $mainwindow->Tk::Error("error message", location ...);
45 $mainwindow is the MainWindow associated with widget which detected the
47 error, "error message" is a string describing the error that has been
48 detected, location is a list of one or more "locations" which describe
49 the call sequence at the point the error was detected.
50 The locations are a typically a mixture of perl location reports giving
52 script name and line number, and simple strings describing locations in
53 core Tk or perl/Tk C code.
54 Tk will ignore any result returned by the Tk::Error method. If another
56 error occurs within the Tk::Error method (for example if it calls die)
57 then Tk reports this error itself by writing a message to stderr (this
58 is to avoid infinite loops due to any bugs in Tk::Error).
59 If several background errors accumulate before Tk::Error is invoked to
61 process them, Tk::Error will be invoked once for each error, in the
62 order they occurred. However, if Tk::Error calls Tk->break, then any
63 remaining errors are skipped without calling Tk::Error.
64 The Tk module includes a default Tk::Error subroutine that simply
66 reports the error on stderr.
67
69 An alternate definition is provided via:
70 "require Tk::ErrorDialog;"
72 that posts a dialog box containing the error message and offers the
74 user a chance to see a stack trace showing where the error occurred.
75 This is an OO implementation of the Tcl/Tk command bgerror, with a
77 twist: since there is only one ErrorDialog widget, you aren't required
78 to invoke the constructor to create it; it will be created
79 automatically when the first background error occurs. However, in
80 order to configure the -cleanupcode and -appendtraceback ErrorDialog
81 options you must call the constructor and create it manually.
82 The ErrorDialog object essentially consists of two subwidgets: a Dialog
84 widget to display the background error and a Text widget for the
85 traceback information. If required, you can invoke various widget
86 methods to customize these subwidgets - their advertised names are
87 described below.
88 $mw->ErrorDialog(-cleanupcode => code, -appendtraceback => bool);
90 $mw is a window reference.
92 code is a CODE reference if special post-background error processing is
94 required (default is undefined). The callback subroutine is called with
95 @_ having the same arguments that Tk::Error was invoked with.
96 bool is a boolean indicating whether or not to append successive
98 tracebacks (default is 1, do append).
99 Advertised ErrorDialog widgets
101 error_dialog is the Dialog widget reference.
102 text is the Text widget reference containing the traceback information.
104
106 If after or fileevent are not invoked as methods of a widget then
107 perl/Tk is unable to provide a $mainwindow argument. To support such
108 code from earlier versions of perl/Tk perl/Tk therefore calls Tk::Error
109 with string 'Tk' instead: Tk->Tk::Error\(...\). In this case the
110 Tk::Error in Tk::ErrorDialog and similar implementations cannot "popup"
111 a window as they don't know which display to use. A mechanism to
112 supply the MainWindow in applications which only have one (a very
113 common case) should be provided.
114
116 Tk::bind Tk::after Tk::fileevent
117
119 background error, reporting
120perl v5.28.0 2018-07-15 Error(3)