Action constructor Null safety

Action(
  1. Function fn,
  2. {ReactiveContext? context,
  3. String? name}
)

Creates an action that encapsulates all the mutations happening on the observables.

Wrapping mutations inside an action ensures the depending observers are only notified when the action completes. This is useful to silent the notifications when several observables are being changed together. You will want to run your reactions only when all the mutations complete. This also helps in keeping the state of your application consistent.

You can give a debug-friendly name to identify the action.

var x = Observable(10);
var y = Observable(20);
var total = Observable(0);

autorun((){
  print('x = ${x}, y = ${y}, total = ${total}');
});

var totalUp = Action((){
  x.value++;
  y.value++;

  total.value = x.value + y.value;
}, name: 'adder');

Even though we are changing 3 observables (x, y and total), the autorun() is only executed once. This is the benefit of action. It batches up all the change notifications and propagates them only after the completion of the action. Actions can also be nested inside, in which case the change notification will propagate when the top-level action completes.

Implementation

factory Action(Function fn, {ReactiveContext? context, String? name}) =>
    Action._(context ?? mainContext, fn, name: name);