Android导航组件和LiveData行为

Question

使用导航组件ViewModel和LiveData时遇到问题。

我在MatchDetailFragment中观察到服务器的响应，并且在收到服务器的响应后，我的MatchDetailFragment得到了有关观察到的实时数据变化的通知，我导航到ScoreFragment，但是当我导航时返回到MatchDetailFragment，观察到的响应将再次得到通知，并尝试再次导航到MatchDetailFragment，并且由于findNavController()的目的地仍为MatchDetailFragment并试图转到nextDestination中未定义的MatchDetailFragment 现在首先我的LiveData应该在我仅按Backstack时得到通知，因为我需要根据响应移至片段B 这是合适的代码

MatchDetailFragment

 override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? {
    val binding: FragmentMatchDetailBinding = DataBindingUtil.inflate(inflater, R.layout.fragment_match_detail, container, false)
    matchDetailViewModel = ViewModelProviders.of(this).get(MatchDetailViewModel::class.java)
    binding.matchDetailViewModel = matchDetailViewModel
    return binding.root
}

override fun onActivityCreated(savedInstanceState: Bundle?) {
    super.onActivityCreated(savedInstanceState)
    matchDetailViewModel.matchDetail.value = args.selctedMatch
    matchDetailViewModel.newMatchSetResponse.observe(viewLifecycleOwner, Observer { resource ->
        when (resource) {
            is Resource.Loading -> {
                showLoading()
            }
            is Resource.Success -> {
                hideLoading()
                with(resource.data) {
                    if (this.body() != null) {
                        val nextDestination = MatchDetailFragmentDirections.nextAction(this.body()!!, args.selctedMatch)
                        findNavController().navigate(nextDestination)
                    } else {
                        root.showSnackbar(this.message(), Snackbar.LENGTH_LONG)
                    }
                }
            }
            is Resource.Failure -> {
                hideLoading()
                root.showSnackbar("Error occurred", Snackbar.LENGTH_LONG)
            }
        }
    })
}

ScoreFragment

  override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? {
        val binding: FragmentScoreBinding = DataBindingUtil.inflate(inflater, R.layout.fragment_score, container, false)
        binding.match = args.matchDetail
        binding.setResponse = args.matchSetResponse
        return binding.root
    }

    override fun onActivityCreated(savedInstanceState: Bundle?) {
        super.onActivityCreated(savedInstanceState)
        scoreViewModel = ViewModelProviders.of(this).get(ScoreViewModel::class.java)
    }