Observer<T> class abstract

An Observer used by the Presenter to subscribe to a UseCase. Ideally, it would be implemented as an inner class inside the Presenter. But, until Dart supports inner classes, this is a workaround.

    /// The [Observer] used to observe the `Observable` of the [LoginUseCase]
    class LoginUseCaseObserver implements Observer<void> {

      // The above presenter
      // This is not optimal, but it is a workaround due to dart limitations. Dart does
      // not support inner classes or anonymous classes.
      final LoginPresenter loginPresenter;

      LoginUseCaseObserver(this.loginPresenter);

      /// implement if the `Observable` emits a value
      // in this case, unnecessary
      void onNext(_) {}

      /// Login is successfull, trigger event in [LoginController]
      void onComplete() {
        // any cleaning or preparation goes here
        assert(loginPresenter.loginOnComplete != null);
        loginPresenter.loginOnComplete();
      }

      /// Login was unsuccessful, trigger event in [LoginController]
      void onError(e) {
        // any cleaning or preparation goes here
        assert(loginPresenter.loginOnError != null);
        loginPresenter.loginOnError(e);
      }

An example where data is retrieved from the UseCase:

    class GetUsersUseCaseObserver implements Observer<void> {

      // The above presenter
      // This is not optimal, but it is a workaround due to dart limitations. Dart does
      // not support inner classes or anonymous classes.
      final UsersPresenter usersPresenter;

      GetUsersUseCaseObserver(this.usersPresenter);

      /// implement if the `Observable` emits a value
      // in this case, unnecessary
      // The parameter depends on what the [UseCase] emits. It could be a list or
      // one `User` at a time
      void onNext(List<User> users) {
        // Any sorting, mapping, filtering of the data goes in here
        assert(usersPresenter.getUsersOnNext != null);
        usersPresenter.getUsersOnNext(users);
      }

      /// Login is successfull, trigger event in [LoginController]
      void onComplete() {
        // any cleaning or preparation goes here
        assert(usersPresenter.getUsersOnComplete != null);
        usersPresenter.getUsersOnComplete();
      }

      /// [UseCase] emitted an error
      void onError(e) {
        assert(usersPresenter.getUsersOnError != null);
        usersPresenter.getUsersOnError(e);
      }

Constructors

Observer()

Properties

hashCode → int

The hash code for this object.

no setter, inherited

runtimeType → Type

A representation of the runtime type of the object.

no setter, inherited

Methods

noSuchMethod(Invocation invocation) → dynamic

Invoked when a nonexistent method or property is accessed.

inherited

onComplete() → void

onError(dynamic e) → void

onNext(T? response) → void

toString() → String

A string representation of this object.

inherited

Operators

operator ==(Object other) → bool

The equality operator.

inherited