exists method
Checks if the appropriate callback exists.
callbackKeySpecify which callback to check.
Returns true if the callback exists, otherwise false.
Implementation
bool exists(dynamic callbackKey) {
if (this._queue.isNotEmpty) {
Here().debugLogAlert(
'Do not check callbacks while callbacks are executing. Call wait() first.',
);
}
return this._callbacks.containsKey(callbackKey);
}