bind method
Implementation
void bind(BuildContext context, {leading = false}) {
_context[context] = this;
final v = _query.subscribe(context, offstage: true);
if (null is T) {
final cb = _callback as EffectCallback<T?>;
if (leading) {
cb.call(context, v);
}
} else if (leading) {
_callback.call(context, v!);
}
}