post<M2> method

_MessageAction<M> post<M2>({
  1. FutureOr<M2> getMessage(
    1. MessageContext msgCtx,
    2. M msg
    )?,
  2. M2? message,
  3. String? label,
})

Posts a new message to be processed by the state machine while a message is being handled.

If getMessage is provided, the function will be evaluated when the transition occurs, and the returned message will be posted. Otherwise a message must be provided.

class DoIt {}
class ItWasDone {}

ItWasDone onDoIt(MessageContext ctx, DoIt msg) {
  print('I did it');
  return ItWasDone();
}
void onItWasDone(MessageContext ctx, ItWasDone msg) => print('It was done');

var state1 = StateKey('s1');
var builder = StateTreeBuilder(initialState: state1);

builder.state(state1, (b) {
  // Handle DoIt message by posting a ItWasDone message for future processing
  b.onMessage<DoIt>((b) => b.stay(action: b.act.post(onDoIt)));
  // Handle ItWasDone message
  b.onMessage<ItWasDone>((b) => b.stay(action: b.act.run(onItWasDone)));
});

This action can be labeled when formatting a state tree by providing a label.

Implementation

_MessageAction<M> post<M2>({
  FutureOr<M2> Function(MessageContext msgCtx, M msg)? getMessage,
  M2? message,
  String? label,
}) {
  if (getMessage == null && message == null) {
    throw ArgumentError('getMessage or message must be provided');
  } else if (getMessage != null && message != null) {
    throw ArgumentError('One of getMessage or message must be provided');
  }
  var _getMessage = getMessage ?? (_, __) => message!;
  return _MessageAction<M>._(
    _ActionType.post,
    (msgCtx, msg) => _getMessage(msgCtx, msg).bind(
      (scheduleMsg) {
        _logger.fine(() => "State '$_forState' is posting message of type $M2");
        msgCtx.post(scheduleMsg as Object);
      },
    ),
    TypeLiteral<M2>().type,
    label,
  );
}