updateTransparency method
- double transparency
 
更新透明度, Android独有
transparency 透明度
Implementation
Future<bool> updateTransparency(double transparency) async {
  if (transparency < 0) {
    return false;
  }
  bool ret = await BMFMapDispatcherFactory.instance.overlayDispatcher
      .updateGroundMember(this.methodChannel,
          {'id': this.Id, 'member': 'transparency', 'value': transparency});
  if (ret) {
    this.transparency = transparency;
  }
  return ret;
}