Tk::after - Execute a command after a time delay
$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?)
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.
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.
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 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.
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.
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.
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.
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.
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.
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.
Tk::Error Tk::callbacks
cancel, delay, idle callback, sleep, time