Task

Handle to async work with cancellation. Cancelled tasks don't update state.

Task<void>? _task;

void search(String query) {
  _task?.cancel();
  _task = launch(() async {
    await Future.delayed(Duration(milliseconds: 300));
    results.setData(await repo.search(query));  // Won't run if cancelled
  });
}

Why Tasks?

Without Piper, async operations need manual mounted checks:

void loadData() async {
  final data = await repo.getData();
  if (mounted) setState(() => _data = data);  // Tedious
}

With Piper, cancelled tasks simply don't update state:

void loadData() => load(data, () => repo.getData());

How It Works

Tasks use "ignore-on-cancel":

• The Future runs to completion (can't stop a Future)
• If cancelled, results are discarded
• Callbacks don't fire, state doesn't update

launch()

Returns a Task handle for manual control:

Task<void>? _task;

void search(String query) {
  _task?.cancel();
  _task = launch(() async {
    await Future.delayed(Duration(milliseconds: 300));
    results.setData(await repo.search(query));
  });
}

launchWith()

Inline success/error callbacks:

launchWith(
  () => repo.save(data),
  onSuccess: (_) => isSaved.value = true,
  onError: (e) => error.value = e.toString(),
);

Task Properties

task.isCancelled  // cancel() was called
task.isCompleted  // Future completed
task.isActive     // running and not cancelled

Await Results

final task = launch(() => fetchData());
final result = await task.result;  // T? - null if cancelled

TaskScope

Manage multiple tasks:

final scope = TaskScope();
scope.launch(() => fetchUsers());
scope.launch(() => fetchPosts());
scope.cancelAll();
scope.dispose();

ViewModels have a built-in taskScope.

Patterns

Debounced Search

Task<void>? _task;

void onQueryChanged(String query) {
  _task?.cancel();
  if (query.isEmpty) return results.setEmpty();

  results.setLoading();
  _task = launch(() async {
    await Future.delayed(Duration(milliseconds: 300));
    results.setData(await repo.search(query));
  });
}

Cancel Previous

Task<void>? _task;

void loadCategory(String id) {
  _task?.cancel();
  _task = launch(() async {
    items.setLoading();
    items.setData(await repo.getItems(id));
  });
}

Sequential Operations

void checkout() {
  launch(() async {
    state.setLoading();
    await cartRepo.validateCart();
    await paymentService.processPayment();
    await orderRepo.createOrder();
    state.setData(null);  // Won't run if user leaves
  });
}