Channel<P> class

Indicates that a value of type P must be provided when entering a state.

Channels are intended as a contract indicating that in order to transition to a particular state, additional contextual information of type P must be provided by the transition source.

// In order to enter the authenticating state, a SubmitCredentials value is
// required.
var authenticatingChannel = Channel<SubmitCredentials>(States.authenticating);

treeBuilder.state(States.loginEntry, (b) {
    b.onMessage<SubmitCredentials>((b) {
      // Provide a SubmitCredentials value when entering authenticating state
      b.enterChannel(authenticatingChannel, (_, msg) => msg);
    });
  }, parent: States.login);

treeBuilder.state(States.authenticating, (b) {
    b.onEnterFromChannel<SubmitCredentials>(authenticatingChannel, (b) {
      // The builder argument provides access to the SubmitCredentials, in this
      // case as as argument to the getMessage function
      b.post<AuthFuture>(getMessage: (_, creds) => _login(creds, authService));
    });
 }, parent: States.login)