Signal

Signal is reactive state that encapsulate a value changing over time. When the value of a signal changes, it automatically notifies its observers.

Syntax

  Signal<T>(T initialValue);

Signal accepts this property:

initialValue: Initial value of T type that the it will hold.

Properties & Methods

Signal provides the following properties and methods:

value: A getter/setter that allows to read and write its state.

Methods inherited from RtState (Learn more here):
- update : A method to notify changes after run a set of instructions.
- refresh : A method to force to notify changes.
- * bind : A method to bind an instance to it.
- * unbind : A method to unbind an instance to it.
- * dispose : A method to remove all listeners and free resources.
* These methods are unnecessary when is declared within a dependency(class registered via the dependecy injection).

Usage

Declaration

Signal can be initialized using the constructor class:

final intSignal = Signal<int>(0);
final strSignal = Signal("initial value");
final userSignal = Signal(User());

In some cases, you may need to declare a state variable that will be initialized later. For this, you can use the late keyword. When using Signal as late within a dependency(class registered via the dependency injection), use Rt.lazyState (Learn more about Lazy state binding). e.g:


3 collapsed lines
1
class CounterController {
2
  final int initialCount;
3

4
  late final count = Rt.lazyState(
5
    () => Signal(this.initialCount),
6
    this
7
  );
3 collapsed lines
8

9
  Counter([this.initialCount = 0]);
10
}

Reading and writing the value

Signal has a value property that allows to read and write its state:

intSignal.value = 10;
print("Current state: ${intSignal.value}");

or also can use the callable function:

intSignal(10);
print("Current state: ${intSignal()}");

or simply use .toString() implicit to get its value as String:

print("Current state: $intSignal");

Updating the value

Use update method to notify changes after run a set of instructions:

userSignal.update((user) {
  user.firstname = "Firstname";
  user.lastname = "Lastname";
});

Use refresh method to force to notify changes.

userSignal.refresh();

Listening to changes

When value has changed, the Signal will emit the following events(learn about it here):

Lifecycle.willUpdate event is triggered before the value change or update , refresh methods have been invoked.
Lifecycle.didUpdate event is triggered after the value change or update , refresh methods have been invoked.

Example of listening to changes:

1
Rt.on(
2
  mySignal,
3
  Lifecycle.didUpdate,
4
  (_, state) => print("State value has changed to: ${state.value}"),
5
);