Execute some code after a given number of seconds, with or without user interaction with
the program.
When to use the ON TIMER trigger?
In some cases, the application needs to execute code on a scheduled basis, for example to process
a message arrived in a queue, refresh data on a dashboard, or display resources in time-based
graphs.
Important: Unlike the ON IDLE trigger which executes when there
is no user activity, the ON TIMER trigger executes even when the user interacts
with the application. Therefore, the code executed in an ON TIMER trigger must
perform quickly, otherwise the end user will experience poor performance. As a general rule, make
sure the time spent in the ON TIMER code is less than the timer interval. For
example, if the processing time takes about 2 seconds, it doesn't make sense to have an ON
TIMER that triggers every second.
Implementing the ON TIMER trigger
To return control to the program on
regular intervals, use the
ON TIMER seconds trigger in dialogs.
This trigger is dialog specific. It is typically defined in the main dialog of the program, but it
can be defined in every dialog.
Important: Consider using the ON TIMER
interaction block in dialogs that do not handle field input, such as DISPLAY ARRAY
and MENU. If used in input dialogs, this trigger may execute in the middle of a
field input, which can force field value validation and raise an input error.
For
example:
DEFINE seconds SMALLINT
LET seconds = 120
DISPLAY ARRAY ...
...
ON TIMER seconds
MESSAGE "Check for messages in queue..."
-- Query the message server for new messages.
...
Note
that the parameter of the
ON TIMER trigger can be a integer variable, but it will
only be read when the dialog is started. Changing the variable during dialog execution will have no
effect.
A value of zero or less than zero disables the timeout trigger.