Question

在“我的视图”模型中创建内部实时数据观察器并将其与数据绑定连接时，我遇到了一个问题。现在，我的代码的一部分看起来像这样：片段：

SearchFragment类：Fragment（），可注入{

@Inject lateinit var viewModelFactory: ViewModelProvider.Factory
@Inject lateinit var searchViewModel: SearchViewModel

private lateinit var disposable: Disposable
private var searchView: SearchView? = null
private var adapter: SearchCityListAdapter? = null

override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? {
    val binding: SearchFragmentBinding = DataBindingUtil.inflate(inflater, R.layout.search_fragment, container, false)
    binding.apply { viewModel = searchViewModel
    setLifecycleOwner(this@SearchFragment)}
    setHasOptionsMenu(true)
    return binding.root
}

override fun onActivityCreated(savedInstanceState: Bundle?) {
    super.onActivityCreated(savedInstanceState)
    searchViewModel = ViewModelProviders.of(this, viewModelFactory).get(SearchViewModel::class.java)
    submitViewModel()
}

    private fun submitViewModel(){
    viewModel.searchCityList.observe(this, Observer {it ->
        if (adapter == null){
            it?.let { adapter = SearchCityListAdapter(it)}.also {createAdapter()}
        } else {
            it?.let { adapter!!.updateList(it) }.also { adapter!!.notifyDataSetChanged() }
        }
    })
    viewModel.responseStatus.observe(this, Observer {
        it?.let { it ->
            when(it.status){
            Status.SUCCESS -> progressBar.visibility = View.INVISIBLE
            Status.FAILURE -> progressBar.visibility = View.INVISIBLE
            Status.ERROR -> progressBar.visibility = View.INVISIBLE
            Status.LOADING ->progressBar.visibility = View.VISIBLE
        } }
    })
}

ViewModel：

class SearchViewModel @Inject constructor(val haloApplication: HaloApplication): ViewModel() {

val progressBarVisibility: MediatorLiveData<Boolean> = MediatorLiveData()
private val responseStatus: MutableLiveData<Response> = MutableLiveData()
val searchCityList: MutableLiveData<SearchCityList> = MutableLiveData()


fun searchCity(cityName: String){
    haloApplication.networkRepository.fetchCityList(cityName, responseStatus, searchCityList)
}

init {
    progressBarVisibility.value = false
    progressBarVisibility.addSource(responseStatus){
        it?.let { when(it.status) {
            Status.FAILURE -> progressBarVisibility.value = false
            Status.ERROR -> progressBarVisibility.value = false
            Status.SUCCESS -> progressBarVisibility.value = false
            Status.LOADING -> progressBarVisibility.value = true
        } }
    }
}

}

XML布局文件：

<?xml version="1.0" encoding="utf-8"?>
<layout
        xmlns:android="http://schemas.android.com/apk/res/android"
        xmlns:tools="http://schemas.android.com/tools">

    <data>
        <variable
                name="viewModel"
                type="com.mbojec.halo.viewmodel.SearchViewModel"/>
    </data>

<FrameLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        tools:context=".ui.SearchFragment">

    <ProgressBar
            style="?android:attr/progressBarStyle"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:id="@+id/progressBar"
            android:layout_gravity="center"
            android:visibility="@{viewModel.progressBarVisibility, default=invisible}"/>


    <androidx.recyclerview.widget.RecyclerView
            android:id="@+id/searchCityListRecycleView"
            android:layout_width="match_parent"
            android:layout_height="match_parent"/>

</FrameLayout>
</layout>

DataBinder文件：

import android.view.View
import androidx.databinding.BindingAdapter

@BindingAdapter("android:visibility")
fun setVisibility(view: View, value: Boolean) {
    view.visibility = if (value) View.VISIBLE else View.INVISIBLE
}

由于某些未知原因，Fragment部分工作正常，但是当responseStatus中发生更改并且通过数据绑定的连接无效时，viewmodel部分永远不会触发。这不是我第一次创建视图模型或转换模型，但这是我第一次遇到这样的问题。我尝试了十几种情况，每次结果都是一样的。首先，我指责新的AndroidX库，但是他们从github上获得的Sunflower示例也可以正常工作，所以我暂时不知道这一点。

Answer 1

MediatorLiveData仅在观察addSource本身时才开始观察通过MediatorLiveData添加的源。由于没有观察到progressBarVisibility，因此您不会收到任何回调。

Answer 2

您必须观察progressBarVisibility才能接收onChanged回调。（每个可观察的对象都需要一个观察对象才能使用）

让我们进行一些更改：

您的progressBarVisibility不必是MediatorLiveData；
您无需公开responseStatus并遵守它；
让您的progressBarVisibility添加responseStatus作为来源。

internal val progressBarVisibility: LiveData<Boolean> = Transformations.map(responseStatus) {
        when (it.status) {
            Status.LOADING -> true
            Status.ERROR, Status.SUCCESS, Status.FAILURE -> false
        }
    }

现在，您可以观察progressBarVisibility并接收回调。

观察者的内部视图模型不会触发

2 个答案: