Summary - Background task

Combine callbackDispatcher and PeriodicTask to sync in background.

Sync flow

A sync flow combines callbackDispatcher and PeriodicTask. First the callback is registered with Workmanager().initialize, then the periodic sync task is scheduled with registerPeriodicTask. On every period callbackDispatcher is called and the sync runs based on the task id.

Workmanager().initialize(callbackDispatcher, isInDebugMode: true);
Workmanager().registerPeriodicTask(
  'sync-task',
  'sync',
  frequency: Duration(minutes: 15),
);

Exercise Write a sync flow

Write a top-level callbackDispatcher function that takes String task and returns true for the 'sync' id. In main, first register the callback with Workmanager().initialize, then schedule a task with registerPeriodicTask using id 'sync-task', callback name 'sync', and a 15 minute frequency, and print 'ok'.

Show example solution

class Workmanager {
  void initialize(Function dispatcher, {bool isInDebugMode = false}) {}
  void registerPeriodicTask(String uniqueId, String taskName, {required Duration frequency}) {}
}

bool callbackDispatcher(String task) {
  if (task == 'sync') {
    return true;
  }
  return false;
}

void main() {
  Workmanager().initialize(callbackDispatcher, isInDebugMode: true);
  Workmanager().registerPeriodicTask(
    'sync-task',
    'sync',
    frequency: Duration(minutes: 15),
  );
  print('ok');
}

Test yourself

In a sync flow, in which order are initialize and registerPeriodicTask called?
- First initialize, then registerPeriodicTask
- Only initialize is enough
- First registerPeriodicTask, then initialize
- Both cannot be called at the same time
Show answer

First initialize, then registerPeriodicTask — First you register the callbackDispatcher with initialize, then schedule the task with registerPeriodicTask; otherwise the callback cannot be found.

Enable debug mode

Workmanager().initialize(callbackDispatcher, ____: true);

Show answer

Workmanager().initialize(callbackDispatcher, isInDebugMode: true);

Sync flow parts

initialize

Callback registration
registerPeriodicTask

Periodic task
callbackDispatcher

Background callback
frequency

Repeat interval

Next lesson: What is MethodChannel?

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