addListener static method
添加监听器 返回id, 用于删除监听器使用
Implementation
static int? addListener(Function? onEvent) {
//event channel 注册
_subscription ??= eventChannel.receiveBroadcastStream('init').listen(_onEvent, onError: _onError);
if (onEvent != null) {
_events[onEvent.hashCode] = onEvent;
getCurrentVolume.then((value) {
onEvent(value);
});
return onEvent.hashCode;
}
return null;
}