once method

bool once(
  1. String topic,
  2. Function callback
)

Registers a callback to listen for the specified event topic. The callback will only be called once for this event.

Returns true if the callback was added, false if it was already added.

Implementation

bool once(String topic, Function callback) {
  if (!_cacheOnce.containsKey(topic)) {
    _cacheOnce[topic] = [];
  }
  if (!_cacheOnce[topic]!.contains(callback)) {
    _cacheOnce[topic]!.add(callback);
    return true;
  }
  return false;
}