pebble/devsite/source/_guides/events-and-services/wakeups.md

title	description	guide_group	order	related_examples	related_docs
Wakeups	Using the Wakeup API to launch an app at some future time.	events-and-services	8	title url Tea Timer https://github.com/pebble-examples/feature-app-wakeup	Wakeup AppLaunchReason launch_reason Timer

The Wakeup API allows developers to schedule an app launch in the future, even if the app itself is closed in the meantime. A wakeup event is scheduled in a similar manner to a Timer with a future timestamp calculated beforehand.

Calculating Timestamps

To schedule a wakeup event, first determine the timestamp of the desired wakeup time as a time_t variable. Most uses of the Wakeup API will fall into three distinct scenarios discussed below.

A Future Time

Call time() and add the offset, measured in seconds. For example, for 30 minutes in the future:

// 30 minutes from now
time_t timestamp = time(NULL) + (30 * SECONDS_PER_MINUTE);

A Specific Time

Use clock_to_timestamp() to obtain a time_t timestamp by specifying a day of the week and hours and minutes (in 24 hour format). For example, for the next occuring Monday at 5 PM:

// Next occuring monday at 17:00 
time_t timestamp = clock_to_timestamp(MONDAY, 17, 0);

Using a Timestamp Provided by a Web Service

The timestamp will need to be translated using the getTimezoneOffset() method available in PebbleKit JS or with any timezone information given by the web service.

Scheduling a Wakeup

Once a time_t timestamp has been calculated, the wakeup event can be scheduled:

// Let the timestamp be 30 minutes from now
const time_t future_timestamp = time() + (30 * SECONDS_PER_MINUTE);

// Choose a 'cookie' value representing the reason for the wakeup
const int cookie = 0;

// If true, the user will be notified if they missed the wakeup 
// (i.e. their watch was off)
const bool notify_if_missed = true;

// Schedule wakeup event
WakeupId id = wakeup_schedule(future_timestamp, cookie, notify_if_missed);

// Check the scheduling was successful
if(id >= 0) {
  // Persist the ID so that a future launch can query it
  const wakeup_id_key = 43;
  persist_write_int(wakeup_id_key, id);
}

After scheduling a wakeup event it is possible to perform some interaction with it. For example, reading the timestamp for when the event will occur using the WakeupId with wakeup_query(), and then perform simple arithmetic to get the time remaining:

// This will be set by wakeup_query()
time_t wakeup_timestamp = 0;

// Is the wakeup still scheduled?
if(wakeup_query(id, &wakeup_timestamp)) {
  // Get the time remaining
  int seconds_remaining = wakeup_timestamp - time(NULL);
  APP_LOG(APP_LOG_LEVEL_INFO, "%d seconds until wakeup", seconds_remaining);
}

To cancel a scheduled event, use the WakeupId obtained when it was scheduled:

// Cancel a wakeup
wakeup_cancel(id);

To cancel all scheduled wakeup events:

// Cancel all wakeups
wakeup_cancel_all();

Limitations

There are three limitations that should be taken into account when using the Wakeup API:

• There can be no more than 8 scheduled wakeup events per app at any one time.

• Wakeup events cannot be scheduled within 30 seconds of the current time.

• Wakeup events are given a one minute window either side of the wakeup time. In this time no app may schedule an event. The return StatusCode of wakeup_schedule() should be checked to determine whether the scheduling of the new event should be reattempted. A negative value indicates that the wakeup could not be scheduled successfully.

The possible StatusCode values are detailed below:

StatusCode	Value	Description
E_RANGE	-8	The wakeup event cannot be scheduled due to another event in that period.
E_INVALID_ARGUMENT	-4	The time requested is in the past.
E_OUT_OF_RESOURCES	-7	The application has already scheduled all 8 wakeup events.
E_INTERNAL	-3	A system error occurred during scheduling.

Handling Wakeup Events

A wakeup event can occur at two different times - when the app is closed, and when it is already launched and in the foreground.

If the app is launched due to a previously scheduled wakeup event, check the AppLaunchReason and load the app accordingly:

static void init() {
  if(launch_reason() == APP_LAUNCH_WAKEUP) {
    // The app was started by a wakeup event.
    WakeupId id = 0;
    int32_t reason = 0;

    // Get details and handle the event appropriately
    wakeup_get_launch_event(&id, &reason);
  }

  /* other init code */

}

If the app is expecting a wakeup to occur while it is open, use a subscription to the wakeup service to be notified of such events:

static void wakeup_handler(WakeupId id, int32_t reason) {
  // A wakeup event has occurred while the app was already open
}

// Subscribe to wakeup service
wakeup_service_subscribe(wakeup_handler);

The two approaches can also be combined for a unified response to being woken up, not depenent on the state of the app:

// Get details of the wakeup
wakeup_get_launch_event(&id, &reason);

// Manually handle using the handler
wakeup_handler(id, reason);