android - 在 fragment 上设置LayoutManager

Question

我创建了一个Fragment，在其中尝试实现recyclerView并加载列表。当我尝试设置 layoutManager 时，问题来了

错误:

java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.v7.widget.RecyclerView.setLayoutManager(android.support.v7.widget.RecyclerView$LayoutManager)' on a null object reference at com.gn.app.Fragments.StationsFragment.onCreateView(StationsFragment.kt:37)

我不能弄清楚什么地方出了问题。

分段:

class StationsFragment : Fragment() {

    companion object {
        val TAG: String = StationsFragment::class.java.simpleName
        fun newInstance() = StationsFragment()
    }

    override fun onCreateView(inflater: LayoutInflater?, container: ViewGroup?, savedInstanceState: Bundle?): View? {
        activity.title = getString(R.string.title_home)
        val view = inflater?.inflate(R.layout.fragment_stations, container, false)

        rcViewStations.layoutManager = LinearLayoutManager(activity)

        val retrofit = Retrofit.Builder()
                .baseUrl(url)
                .addConverterFactory(GsonConverterFactory.create())
                .build()

        val stations = retrofit.create(StationService::class.java)

        val call = stations.getStations()

        call.enqueue(object : Callback<ResponseStations> {

            override fun onResponse(call: Call<ResponseStations>?, response: Response<ResponseStations>?) {
                if (response?.code() == 200) {
                    loadData(response.body()?.stations)
                }
            }

            override fun onFailure(call: Call<ResponseStations>?, t: Throwable?) {
                //TODO: Implement error response.
            }

        })

        return view
    }

    private fun loadData(stations: List<StationsItem?>?) {
        val items = stations?.map {
            it?.let {
                Station(name, long, lat)
            }
        }
        rcViewStations.adapter = AdapterStation(items)
    }
}

实用程序

fun ViewGroup.inflate(layoutId: Int): View {
    return LayoutInflater.from(context).inflate(layoutId, this, false)
}

片段xml

<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    tools:context="com.gn.app.Fragments.StationsFragment">

    <android.support.v7.widget.RecyclerView
        android:id="@+id/rcViewStations"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        app:behavior_overlapTop="30dp"
        app:layout_behavior="@string/appbar_scrolling_view_behavior" />

</FrameLayout>

项目xml

<?xml version="1.0" encoding="utf-8"?>
<android.support.v7.widget.CardView xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:layout_margin="5dp"
    android:orientation="vertical">

        <LinearLayout
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:orientation="vertical"
            android:padding="10dp">

            <TextView
                android:id="@+id/txtStationName"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:textAppearance="@style/TextAppearance.AppCompat.Large"
                android:transitionName="transitionTitle"
                tools:text="Name" />

            <TextView
                android:id="@+id/txtStationDistance"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:textAppearance="@style/TextAppearance.AppCompat.Small"
                android:transitionName="transitionDesc"
                tools:text="0.00 m" />

            <TextView
                android:id="@+id/txtStationBikes"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:textAppearance="@style/TextAppearance.AppCompat.Small"
                android:transitionName="transitionDesc"
                tools:text="12" />

            <TextView
                android:id="@+id/txtStationSlots"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:textAppearance="@style/TextAppearance.AppCompat.Small"
                android:transitionName="transitionDesc"
                tools:text="22" />

            <TextView
                android:id="@+id/txtStationDate"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_gravity="end"
                android:textAppearance="@style/TextAppearance.AppCompat.Medium"
                android:textColor="@color/colorAccent"
                android:transitionName="transitionPrice"
                tools:text="Date" />

        </LinearLayout>

</android.support.v7.widget.CardView>

Answer 1

rcViewStations为null，异常如何表示。
看来您正在使用内部使用getView()的kotlin android扩展。
getView()只能在onCreateView完成后返回一个值。

您可以使用onViewCreated进行所有 View 操作逻辑，也可以通过findViewById在新创建的 View 上使用inflater?.inflate(R.layout.fragment_stations, container, false)来访问RecyclerView