after(3pm) User Contributed Perl Documentation after(3pm)NAMETk::after - Execute a command after a time delay
SYNOPSIS
$widget->after(ms)
$id = $widget->after(ms?,callback?)
$id = $widget->repeat(ms?,callback?)
$widget->afterCancel($id)
$id = $widget->afterIdle(callback)
$widget->afterInfo?($id)?
$id->time(?delay?)
DESCRIPTION
This method is used to delay execution of the program or to execute a
callback in background sometime in the future.
In perl/Tk $widget->after is implemented via the class "Tk::After", and
callbacks are associated with $widget, and are automatically cancelled
when the widget is destroyed. An almost identical interface, but
without automatic cancel, and without repeat is provided via Tk::after
method.
Internal Details
The internal Tk::After class has the following synopsis:
$id = Tk::After->new($widget, tid, $time, 'once', callback);
$id = Tk::After->new($widget, tid, $time, 'repeat', callback);
$id->cancel;
$id->time(?delay?);
$id is a Tk::After object, an array of 5 elements:
$widget is the parent widget reference.
tid is the internal timer id, a unique string.
$time is the string 'idle', representing an idle queue timer, or a
integer millisecond value.
once or repeat specifies whether the timer is a one-time after event,
or a repeating repeat event.
callback specifies a Perl/Tk Tk::Callback object.
Changing a repeat timer interval
It's possible to change a repeat timer's delay value, or even cancel
any timer, using the time method. If delay is specified and non-zero, a
new timer delay is established. If delay is zero the timer event is
canceled just as if $id->cancel were invoked. In all cases the current
millisecond timer delay is returned.
Note: the new timer delay will take effect on the subsequent timer
event - this command will not cancel the pending timer event and re-
issue it with the new delay time.
The after() method has several forms as follows:
$widget->after(ms)
The value ms must be an integer giving a time in milliseconds. The
command sleeps for ms milliseconds and then returns. While the
command is sleeping the application does not respond to events.
$widget->after(ms,callback)
In this form the command returns immediately, but it arranges for
callback be executed ms milliseconds later as an event handler.
The callback will be executed exactly once, at the given time. The
command will be executed in context of $widget. If an error occurs
while executing the delayed command then the Tk::Error mechanism is
used to report the error. The after command returns an identifier
(an object in the perl/Tk case) that can be used to cancel the
delayed command using afterCancel.
$widget->repeat(ms,callback)
In this form the command returns immediately, but it arranges for
callback be executed ms milliseconds later as an event handler.
After callback has executed it is re-scheduled, to be executed in a
futher ms, and so on until it is cancelled.
$widget->afterCancel($id)
$id->cancel
Cancels the execution of a delayed command that was previously
scheduled. $id indicates which command should be canceled; it
must have been the return value from a previous after command. If
the command given by $id has already been executed (and is not
scheduled to be executed again) then afterCancel has no effect.
$widget->afterCancel(callback)
This form is not robust in perl/Tk - its use is deprecated. This
command should also cancel the execution of a delayed command. The
callback argument is compared with pending callbacks, if a match is
found, that callback is cancelled and will never be executed; if
no such callback is currently pending then the afterCancel has no
effect.
$widget->afterIdle(callback)
Arranges for callback to be evaluated later as an idle callback.
The script will be run exactly once, the next time the event loop
is entered and there are no events to process. The command returns
an identifier that can be used to cancel the delayed command using
afterCancel. If an error occurs while executing the script then
the Tk::Error mechanism is used to report the error.
$widget->afterInfo?($id)?
This command returns information about existing event handlers. If
no $id argument is supplied, the command returns a list of the
identifiers for all existing event handlers created by the after
and repeat commands for $widget. If $id is supplied, it specifies
an existing handler; $id must have been the return value from some
previous call to after or repeat and it must not have triggered yet
or been cancelled. In this case the command returns a list with
three elements. The first element of the list is the callback
associated with $id, the second element is either idle or the
integer timer millisecond value to indicate what kind of event
handler it is, and the third is a string once or repeat to
differentiate an after from a repeat event.
The after(ms) and afterIdle forms of the command assume that the
application is event driven: the delayed commands will not be executed
unless the application enters the event loop. In applications that are
not normally event-driven, the event loop can be entered with the vwait
and update commands.
SEE ALSO
Tk::Error Tk::callbacks
KEYWORDS
cancel, delay, idle callback, sleep, time
perl v5.26.0 2017-07-22 after(3pm)
