Question

基于一项活动和一些片段的应用程序。片段启动时，应用程序崩溃并显示日志：

java.lang.RuntimeException: Unable to start activity ComponentInfo{ru.alexsuvorov.paistewiki/ru.alexsuvorov.paistewiki.StartDrawer}: java.lang.NullPointerException
                  ...
               Caused by: java.lang.NullPointerException
                  at ru.alexsuvorov.paistewiki.Fragment.NewsFragment.onCreateView(NewsFragment.java:42)

我只是初始化一些数组位置，然后尝试显示它

现在我编辑代码

public class NewsFragment extends Fragment {

private static final String TAG = "NewsFragment";
private ImageSliderAdapter sliderAdapter;
private List<NewsMonth> monthArray;

public View onCreateView(@NonNull LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
    return inflater.inflate(R.layout.news_fragment, container, false);
}
@Override
public void onViewCreated(@NonNull View view,
                          Bundle savedInstanceState){
    super.onViewCreated(view, savedInstanceState);
    ViewPager viewPager = view.findViewById(R.id.view_pager);
    sliderAdapter = new ImageSliderAdapter(getContext());
    viewPager.setAdapter(sliderAdapter);

    initializeData();
    RecyclerView recyclerView = view.findViewById(R.id.newsList);
    LinearLayoutManager llm = new LinearLayoutManager(getActivity());
    recyclerView.setLayoutManager(llm);
    NewsAdapter adapter = new NewsAdapter(monthArray); /*this.getContext(), R.layout.news_item, monthArray*/
    recyclerView.setAdapter(adapter);
}

private void initializeData() {
    monthArray = new ArrayList<>();
    monthArray.add(new NewsMonth("www.ya.ru", "Январь", null));
    monthArray.add(new NewsMonth("www.on.ru", "Февраль", null));
    monthArray.add(new NewsMonth("www.ti.ru", "Март", null));
}

}

我的XML文件-回收清单和卡片项目： ... .... ...

<android.support.v7.widget.RecyclerView 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:id="@+id/newsLayout"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_margin="8dp"
android:orientation="vertical"
android:padding="8dp">
<android.support.v4.view.ViewPager
    android:id="@+id/view_pager"
    layout_constraintEnd_toStartOf="@+id/newsList"
    android:layout_width="match_parent"
    android:layout_height="103dp"
    app:layout_constraintEnd_toStartOf="parent"
    app:layout_constraintStart_toStartOf="parent"
    app:layout_constraintTop_toTopOf="parent">
</android.support.v4.view.ViewPager>
<ScrollView
    android:id="@+id/newsScroll"
    android:layout_width="match_parent"
    android:layout_height="433dp"
    android:paddingEnd="@dimen/fab_margin"
    app:layout_anchor="@+id/view_pager"
    app:layout_anchorGravity="bottom"
    app:layout_constraintTop_toBottomOf="@id/view_pager"
    tools:layout_constraintTop_toBottomOf="@+id/view_pager"
    android:paddingRight="@dimen/fab_margin">
    <android.support.v7.widget.RecyclerView
        android:id="@+id/newsList"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:gravity="top|bottom|left|right"
        android:orientation="vertical"
        app:layout_anchor="@+id/view_pager"
        app:layout_anchorGravity="bottom|center"
        app:layout_constraintTop_toBottomOf="@id/view_pager"
        tools:layout_editor_absoluteX="3dp"
        tools:layout_editor_absoluteY="112dp">
    </android.support.v7.widget.RecyclerView>
</ScrollView>

和卡片项目： 一些字符的文本，以使堆栈不会发誓 一些字符的文本，以使堆栈不会发誓 一些字符的文本，以使堆栈不会发誓 一些字符的文本，以使堆栈不会发誓

<android.support.v7.widget.CardView 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:id="@+id/cv"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_marginBottom="8dp"
android:background="@color/black"
app:cardCornerRadius="8dp"
app:cardUseCompatPadding="true"
app:contentPadding="0dp">

<RelativeLayout
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:padding="16dp">

    <TextView
        android:id="@+id/news_label"
        android:layout_width="255dp"
        android:layout_height="wrap_content"
        android:layout_alignParentLeft="true"
        android:layout_alignParentStart="true"
        android:layout_alignParentTop="true"
        android:layout_marginTop="5dp"
        android:background="@color/colorAccent"
        tools:text="Who is.. James bond??!" />


    <TextView
        android:id="@+id/news_category"
        android:layout_width="60dp"
        android:layout_height="wrap_content"
        android:layout_alignBaseline="@+id/news_label"
        android:layout_alignBottom="@+id/news_label"
        android:layout_toEndOf="@+id/news_label"
        android:layout_toRightOf="@+id/news_label"
        android:background="@android:color/holo_green_light"
        tools:text="Artist" />

</RelativeLayout>

<TextView
    android:id="@+id/month_name"
    android:layout_width="150dp"
    android:layout_height="20dp"
    android:layout_alignParentTop="true"
    android:background="@color/colorPrimaryDark"
    android:fontFamily="sans-serif-condensed"
    android:gravity="center"

    android:textSize="16sp"
    android:textStyle="bold"
    tools:text="Июнь" />

Answer 1

请勿在OnCreateView内编写findViewById（）语句。仅使用OnCreateView（）扩大视图。在OnViewCreated（）方法中编写findViewById（）方法，该方法将在视图创建完成后立即调用。
通过在onCreateView（）中编写findViewById（），您试图在容器View仍处于创建过程中并且您可能尚未创建视图的情况下查找视图。

片段在onCreateView（）中的recyclerView上为null

1 个答案: