在Android中未调用具有ViewModel onChanged的可变实时数据

Question

我正在尝试采用如下viewModel配置的实时数据概念，

final BannersViewmodel  bannermodel = ViewModelProviders.of(this).get(BannersViewmodel.class);
        bannermodel.getUserMutableLiveData().observe(DashBoardActivity.this, new Observer<ArrayList<BannersModel>>() {
            @Override
            public void onChanged(ArrayList<BannersModel> bannersModels) {
                Log.e("onChanged","BannersCalled");
            }
        });

从服务器获取结果时未调用onChanged方法。请提供任何解决方案。.