ListAdapter 未使用来自 livedata

如何解决ListAdapter 未使用来自 livedata

我使用带 MVVM 的 firebase firestore 下载数据，我使用存储库层在应用程序级别获取和保存数据，使用 viewModel 层观察更改并调用存储库，以及显示数据的片段.问题是，即使我可以成功获取数据，它也没有显示在 recyclerview 上。

存储库类：

fun fetchAppsFromFirestore() {

    val list = mutableListOf<AppModel>()

    firestore.collection(APPS_COLLECTION).get().addOnSuccessListener { querySnapshot ->

        for (doc in querySnapshot) {
            val app = doc.toObject(AppModel::class.java).also {
                it.docId = doc.id
            }
            list.add(app)
        }
        
        //This is a global mutableLiveData
        readingLiveData.value = list

    }
}

ViewModel 类：

fun getData() : LiveData<AppModelReadingResponse> {
    repo.fetchAppsFromFirestore()
    return repo.readingLiveData
}

到目前为止，代码做了它应该做的事情，如果我登录 viewModel，列表中的所有项目都在那里。

适配器类：

class FeaturedAppAdapter(val context: Context) :
ListAdapter<AppModel,FeaturedAppAdapter.FeaturedAppViewHolder>(AppModelComparator()) {

class AppModelComparator : DiffUtil.ItemCallback<AppModel>() {
    override fun areItemsTheSame(oldItem: AppModel,newItem: AppModel): Boolean {
        return oldItem.docId == newItem.docId
    }

    override fun areContentsTheSame(oldItem: AppModel,newItem: AppModel): Boolean {
        return oldItem == newItem
    }

}


inner class FeaturedAppViewHolder(private val binder: RowFeaturedAppsBinding) :
    RecyclerView.ViewHolder(binder.root) {

    fun bind(app: AppModel) {

        binder.rowFeaturedAppsTxtAppName.text = app.appName
        binder.rowFeaturedAppsTxtAppDescription.text = app.appDesc

    }
}

override fun onCreateViewHolder(parent: ViewGroup,viewType: Int): FeaturedAppViewHolder {
    return FeaturedAppViewHolder(
        RowFeaturedAppsBinding.inflate(
            LayoutInflater.from(parent.context),parent,false
        )
    )
}

override fun onBindViewHolder(holder: FeaturedAppViewHolder,position: Int) {

    val app = getItem(position)
    holder.bind(app)

}

}

在我检索数据的片段上：

class HomeFragment : Fragment() {

companion object {
    private const val TAG = "tag_log_info"
}

//Layout components
private val binder by lazy {
    FragmentHomeBinding.inflate(layoutInflater)
}


//ViewModel
private val appsViewModel: AppsViewModel by viewModels {
    AppsViewModelFactory((requireActivity().application as MyApplication).appsRepository)
}

//RecyclerView
private lateinit var mAdapter: FeaturedAppAdapter

override fun onCreateView(
    inflater: LayoutInflater,container: ViewGroup?,savedInstanceState: Bundle?
): View {

    
    setupRecyclerView()

    return binder.root
}

private fun setupRecyclerView() {

    mAdapter = FeaturedAppAdapter(requireContext())

    with(binder.fragmentHomeRecyclerView){
        this.adapter = mAdapter
        this.layoutManager = LinearLayoutManager(requireContext(),LinearLayoutManager.VERTICAL,false)
        this.setHasFixedSize(true)
    }

    observeData()
}

private fun observeData() {

    appsViewModel.getData().observe(viewLifecycleOwner) {
        Log.i(TAG,"observeData: $it") // This log shows that the data is here
        mAdapter.submitList(it)
    }

}

}

所以问题是，即使日志显示我有片段上的数据列表，当我调用 submitList(it) 时，没有任何反应，我无法弄清楚原因。我在这里做错了什么？

解决方法

在将数据设置为适配器后，在observeData 函数中，您必须调用notifyDataSetChanged 函数以让适配器知道数据发生了变化。

所以你的观察者函数变成了

 private fun observeData() {
    appsViewModel.getData().observe(viewLifecycleOwner) {
      Log.i(TAG,"observeData: ${it.list}") // This log shows that the data is here
      mAdapter.submitList(it.list)
      mAdapter.notifyDataSetChanged()
   }
}

如果这不起作用，请告诉我。