UseState

UseState is a hook that allows to declare state variables and manipulate its value, which in turn notifies about its changes to listeners.

Syntax

UseState<T>(T initialValue, { String? debugLabel });

UseState accepts these parameters:

• initialValue: Initial value of T type that it will hold.
• debugLabel: (optional) A label to identify the hook in the DevTools extension.

Properties & Methods

UseState provides the following properties and methods:

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

Properties and methods inherited from RtState

• debugLabel: A string that represents the label of the state object for debugging purposes.
• debugInfo: A map that contains debug information about the state object.

• update : Executes a callback function and notify its observers that the state has changed. When it is invoked, it emits two lifecycle events to signal the state transition:
  • Lifecycle.willUpdate is emitted first, indicating the impending update.
  • Lifecycle.didUpdate is emitted once the update process is complete.
• notify : Forces the state to notify its observers. Unlike update , it emits only the Lifecycle.didUpdate event, as it doesn’t involve any preparatory steps before the notification.
• bind : Establishes a connection between the state and a specific instance. This connection allows the instance to reactively update based on changes to the state. By binding the state, the instance becomes aware of changes to the state and can appropriately reflect those changes in its behavior.
• unbind : Releases the connection between the state and the instance. When unbinding, the instance will no longer receive updates from the state. This can be useful when an instance is no longer actively using the state or when it needs to detach from the state temporarily or permanently.
• dispose : Is responsible for cleaning up the state and any associated observers or resources. Disposing of the state ensures that it is properly released and no longer consumes memory or processing resources unnecessarily.

Note

While the bind , unbind and dispose methods are normally used to manage the lifecycle of a state, Reactter handles this automatically, when the state is declared inside an instance that exists within Reactter’s context via the dependecy injection, so you don’t need to worry about it(Learn more about Binding State to Dependency).

Usage

Declaration

UseState can be initialized using the constructor class:

final intState = UseState<int>(0);
final strState = UseState("initial value");
final userState = UseState(User());

Note

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 UseState as late within a dependency(class registered via the dependency injection), use Rt.lazyState (Learn more about Lazy state binding). e.g:

counter_controller.dart

class CounterController {
  final int initialCount;

  late final count = Rt.lazyState(
    () => UseState(this.initialCount),
    this,
  );

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

Reading and writing the value

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

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

Note

UseState notifies that its value has changed when the previous value is different from the current value. If its value is an Object , it does not detect internal changes, only when value is setted to another Object . Learn more about updating objects in state.

Updating the state

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

uState.update((value) {
  uState.value = "New value";
});

Use notify method to force to notify changes.

userState.notify();

Listening to changes

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

• Lifecycle.willUpdate event is triggered before the change in value or update method have been invoked.
• Lifecycle.didUpdate event is triggered after the change in value or after update or notify methods have been invoked.

Example of listening to changes:

Rt.on(
  myState,
  Lifecycle.didUpdate,
  (_, state) => print("State value has changed to: ${state.value}"),
);