android - 实时数据中的 Observables 更新在 fragment 中不起作用

Question

我有一个实例化 koin 注入(inject)的 View 模型实例的 fragment ，问题是，观察到的属性之一在 View 模型的 postValue () 操作之后没有在 fragment 中被激发，它根本没有进入方法在 fragment 中，即使它已经更新。

fragment :

class ListFragment : Fragment() {

private lateinit var adapter: PostAdapter
private val viewModel: PostsViewModel by viewModel()
private var _binding: ListFragmentBinding? = null
private var defaultTopic = "news"
private var afterPage: String = ""

override fun onCreateView(
        inflater: LayoutInflater, container: ViewGroup?,
        savedInstanceState: Bundle?
): View? {
    return inflater.inflate(R.layout.list_fragment, container, false)
}

override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    setHasOptionsMenu(true)
}

override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
    super.onViewCreated(view, savedInstanceState)
    _binding = ListFragmentBinding.bind(view)

    adapter = PostAdapter(mutableListOf(), requireContext()) {
        val action = ListFragmentDirections.openDetailsFragment(it)
        findNavController().navigate(action)
    }

    _binding?.let{
        val llm = LinearLayoutManager(requireContext())
        it.recyclerviewPosts.layoutManager = llm
        it.recyclerviewPosts.adapter = adapter

        recyclerViewListenerSetup(it, llm)
    }
    setupObservers()

}

private fun recyclerViewListenerSetup(it: ListFragmentBinding, llm: LinearLayoutManager) {
    it.recyclerviewPosts.addOnScrollListener(object : RecyclerView.OnScrollListener() {
        override fun onScrolled(recyclerView: RecyclerView, dx: Int, dy: Int) {
            super.onScrolled(recyclerView, dx, dy)
            val visibleItemCount: Int = llm.childCount
            val totalItemCount: Int = llm.itemCount
            val firstVisibleItemPosition: Int = llm.findFirstVisibleItemPosition()

            if((visibleItemCount + firstVisibleItemPosition) >= totalItemCount
                    && firstVisibleItemPosition >= 0) {
                viewModel.getNextPage(defaultTopic, afterPage)
            }
        }
    })
}

private fun setupObservers(){
    viewModel.getPostList(defaultTopic)
    viewModel.posts.observe(this as LifecycleOwner, { posts ->
        if (posts.isSuccess && posts.getOrNull() != null) {
            adapter.updateList(posts.getOrNull()!! as MutableList<PostsDTO>)
            afterPage = posts.getOrNull()!![0].after
            showList()
        } else {
            showError()
        }
    })
    viewModel.loading.observe(this as LifecycleOwner, {
        if (it) {
            showLoading()
        } else {
            hideLoading()
        }
    })
    viewModel.next.observe(this as LifecycleOwner, {
        if (it.isSuccess && it.getOrNull() != null) {
            adapter.addList(it.getOrNull() as MutableList<PostsDTO>)
            afterPage = it.getOrNull()!![0].after
        }
    })
}

private fun showList(){
    _binding?.let {
        it.recyclerviewPosts.visibility = VISIBLE
    }
}

private fun showLoading(){
    _binding?.let {
        it.loading.visibility = VISIBLE
        it.containerError.root.visibility = GONE
        it.recyclerviewPosts.visibility = GONE
    }
}

private fun hideLoading(){
    _binding?.let {
        it.loading.visibility = GONE
    }
}

private fun showError() {
    _binding?.let {
        it.containerError.root.visibility = VISIBLE
        it.recyclerviewPosts.visibility = GONE
    }
}

override fun onCreateOptionsMenu(menu: Menu, inflater: MenuInflater) {
    inflater.inflate(R.menu.menu_main, menu)
    val searchItem = menu.findItem(R.id.action_search)
    val searchManager =
        requireActivity().getSystemService(Context.SEARCH_SERVICE) as SearchManager
    val searchView = searchItem.actionView as SearchView
    searchView.setSearchableInfo(searchManager.getSearchableInfo(activity?.componentName))

    searchView.apply {
        queryHint = "Search SubReddit"
        setOnQueryTextListener(object : SearchView.OnQueryTextListener {
            override fun onQueryTextSubmit(query: String?): Boolean {
                defaultTopic = query!!
                viewModel.getPostList(defaultTopic)
                return false
            }

            override fun onQueryTextChange(newText: String?): Boolean {
                return true
            }
        })
    }
    super.onCreateOptionsMenu(menu, inflater)
}

}

我尝试在recyclerView滚动时调用viewmodel方法来更新显示的列表。

View 模型:

class PostsViewModel(private val repository: PostsRepository) : ViewModel(){

private val _posts = MutableLiveData<Result<List<PostsDTO>>>()
val posts: LiveData<Result<List<PostsDTO>>>
    get() =_posts

private val _loading = MutableLiveData<Boolean>()
val loading: LiveData<Boolean>
    get() = _loading

private val _next = MutableLiveData<Result<List<PostsDTO>>>()
val next: LiveData<Result<List<PostsDTO>>>
    get() =_posts

fun getPostList(q: String){
    viewModelScope.launch {
        _loading.postValue(true)
        repository.fetchPosts(q)
            .collect {
                _posts.value = it
            }
        _loading.postValue(false)
    }
}

fun getNextPage(topic: String, afterPage: String) {
    viewModelScope.launch {
        repository.fetchNextPage(topic, afterPage)
                .collect{
                    _next.postValue(it)
                }
    }
}

 }

这种情况下next方法的请求结果已经更新viewmodel后，fragment在viewmodel.next.observer()中不被激发

Answer 1

哎呀!经过单元测试后，我能够找出问题所在，问题出在 ctrl + v，下一个属性，它返回的是 _post 属性而不是 _next 属性，因此未通知 View 更新。修正修正在viewmoldel中，改变下一个变量的get方法:

private val _next = MutableLiveData<Result<List<PostsDTO>>>()
val next: LiveData<Result<List<PostsDTO>>>
    get() =_next