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.
- $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.
cancel, delay, idle callback, sleep, time