使用rxkotlin填充RecyclerView：RecyclerView保持为空

Question

这里是一个 Kotlin 活动，应该显示一个事件列表（来自 sample.json）。

class TalksActivity : AppCompatActivity(), TalkAdapter.Listener {

private val TAG = TalksActivity::class.java.simpleName

private var mCompositeDisposable: CompositeDisposable? = null
private var mAdapter: TalkAdapter? = null
private var disposable: Disposable? = null
private val mapper = createMapper()

override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    setContentView(R.layout.activity_talks)
    pbWaiting.visibility = View.VISIBLE

    mCompositeDisposable = CompositeDisposable()

    initRecyclerView()
    loadTalks()
}


private fun initRecyclerView() {
    rv_talks_list.setHasFixedSize(true)
    val layoutManager: RecyclerView.LayoutManager = LinearLayoutManager(this)
    rv_talks_list.layoutManager = layoutManager
    rv_talks_list.adapter = TalkAdapter(ArrayList(Collections.emptyList()), this)
}

private fun loadTalks() {
    disposable = getTalks()
            .subscribeOn(AndroidSchedulers.mainThread())
            .observeOn(Schedulers.io())
            .subscribe ({ result -> handleResponse(result) }, { error -> handleError(error) })
}

private fun handleResponse(talkList: List<Talk>) {
    mAdapter = TalkAdapter(ArrayList(talkList), this)
    rv_talks_list.adapter = mAdapter
    pbWaiting.visibility = View.GONE
}

private fun handleError(error: Throwable) {
    pbWaiting.visibility = View.GONE
    throw error
}

private fun createMapper(): ObjectMapper {
    val mapper = jacksonObjectMapper()
    mapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false)
    return mapper
}

override fun onItemClick(talk: Talk) {
    startActivity(CountdownActivity.newIntent(this, talk))
}

private fun getTalks() : Observable<List<Talk>> {
    val text = resources.openRawResource(R.raw.sample).bufferedReader().use { it.readText() }
    val typeFactory = mapper.typeFactory
    val collectionType = typeFactory.constructCollectionType(ArrayList::class.java, Talk::class.java)
    return Observable.create<List<Talk>> {
        mapper.readValue(text, collectionType)
    }
}

}

问题：当我调用loadTalks()时，handleResponse(result)或handleError(error)从未被调用，屏幕仅显示白色并显示进度条。

控制台中没有错误信息。

这是我的非常简单的activity_talks.xml文件：

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".TalksActivity">

<android.support.v7.widget.RecyclerView
    android:id="@+id/rv_talks_list"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    app:layout_constraintBottom_toBottomOf="parent"
    app:layout_constraintLeft_toLeftOf="parent"
    app:layout_constraintRight_toRightOf="parent"
    app:layout_constraintTop_toTopOf="parent" />

<ProgressBar
    android:id="@+id/pbWaiting"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:visibility="gone"
    app:layout_constraintBottom_toBottomOf="parent"
    app:layout_constraintEnd_toEndOf="parent"
    app:layout_constraintHorizontal_bias="0.5"
    app:layout_constraintStart_toStartOf="parent"
    app:layout_constraintTop_toTopOf="parent" />

</android.support.constraint.ConstraintLayout>

有什么问题吗？

在没有使用 rxKotlin 和 observable 代码的情况下，这个代码是可以工作的。

编辑

这是我的适配器：

class TalkAdapter(private val dataList: ArrayList<Talk>, private val listener: Listener) : RecyclerView.Adapter<TalkAdapter.ViewHolder>() {

interface Listener {

    fun onItemClick(talk: Talk)
}

private val colors: Array<String> = arrayOf("#EF5350", "#EC407A", "#AB47BC", "#7E57C2", "#5C6BC0", "#42A5F5")

override fun onBindViewHolder(holder: ViewHolder, position: Int) {
    holder.bind(dataList[position], listener, colors, position)
}

override fun getItemCount(): Int = dataList.count()

override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): ViewHolder {

    val view = LayoutInflater.from(parent.context).inflate(R.layout.adapter_talk, parent, false)

    return ViewHolder(view)
}

class ViewHolder(view: View) : RecyclerView.ViewHolder(view) {

    fun bind(talk: Talk, listener: Listener, colors: Array<String>, position: Int) {

        itemView.title.text = talk.title
        itemView.recap.text = talk.summary
        itemView.eventId.text = talk.eventId
        itemView.setBackgroundColor(Color.parseColor(colors[position % 6]))

        itemView.setOnClickListener { listener.onItemClick(talk) }
    }
}
}

编辑

感谢Demigod的答案，我找到了解决方案。

当我使用Observable.create创建一个Observable时，必须手动触发onNext()和onError()。

要修复它，请更改

private fun getTalks() : Observable<List<Talk>> {
    val text = resources.openRawResource(R.raw.sample).bufferedReader().use { it.readText() }
    val typeFactory = mapper.typeFactory
    val collectionType = typeFactory.constructCollectionType(ArrayList::class.java, Talk::class.java)
    return Observable.create<List<Talk>> {
        mapper.readValue(text, collectionType)
    }
}

使用

private fun getTalks(): Observable<List<Talk>> {
    val text = resources.openRawResource(R.raw.sample).bufferedReader().use { it.readText() }
    val typeFactory = mapper.typeFactory
    val collectionType = typeFactory.constructCollectionType(ArrayList::class.java, Talk::class.java)
    return Observable.fromCallable { mapper.readValue<List<Talk>>(text, collectionType) }
}

为了更好的性能：

private fun getTalks(): Observable<List<Talk>> {
    return Observable.fromCallable {
        val text = resources.openRawResource(R.raw.sample).bufferedReader().use { it.readText() }
        val typeFactory = mapper.typeFactory
        val collectionType = typeFactory.constructCollectionType(ArrayList::class.java, Talk::class.java)
        mapper.readValue<List<Talk>>(text, collectionType)
    }
}

- psv

Answer 1

您需要更改您的代码。您正在订阅 mainThread 而不是后台线程。请参考以下代码：

 disposable = getTalks()
            .subscribeOn(Schedulers.io())
            .observeOn(AndroidSchedulers.mainThread())
            .subscribe ({ result -> handleResponse(result) }, { error -> handleError(error) })

- Anand Jain

---

谢谢，这是一个好的观察。我已经进行了更改，但是 handleResponse(result) 或者 handleError(error) 仍然没有被调用。 - psv

Answer 2

这应该是代码。希望这能帮到你。

disposable = getTalks()
        .subscribeOn(Schedulers.io())
        .observeOn(AndroidSchedulers.mainThread())
        .subscribeBy (onNext = { handleResponse(it) }, onError = { handleError(it)}

- Indranil Dutta

Answer 3

我认为问题在于您创建Observable的方式：

 return Observable.create<List<Talk>> {
      mapper.readValue(text, collectionType)
 }

当您使用Observable.create创建可观察对象时，应该手动发出新项目，如下所示：

Observable.create<Int> { e: ObservableEmitter<Int> ->
    e.onNext(1)
}

在你的情况下，你应该使用 Observable.fromCallable { } 或者 Single.fromCallable { }，因为它只会返回单个结果。

- Demigod

---

我明白你的意思，但是当我将return Observable.create<List<Talk>> { mapper.readValue(text, collectionType) }替换为return Observable.fromCallable(mapper.readValue(text, collectionType))时，我遇到了一个错误：Caused by: java.lang.ClassCastException: java.util.ArrayList cannot be cast to java.util.concurrent.Callable。 - psv

@psv 请将其更改为：Observable.fromCallable { mapper.readValue(text, collectionType) } - Demigod

我尝试了一下，但编译器抱怨道：类型推断失败：没有足够的信息推断函数参数T。请明确指定它。(readValue用红线标出) - psv

@psv，我明白了。readValue方法的签名是什么？实际上，我认为你可以这样做：Observable.fromCallable { mapper.readValue<List<Talk>>(text, collectionType) }。 - Demigod

签名为 public <T> T readValue(String content, JavaType valueType)。是的，它有效！谢谢你，半神。我也写了一些能够工作的东西：return Observable.fromCallable { val result: List<Talk> = mapper.readValue(text, collectionType) result } 但是你的解决方案更好！谢谢 - psv