Question

我想为RecyclerView构建自定义适配器，但是当我为任何视图设置Text或设置值时，它返回NullPointerException。我不是为什么。尝试了许多解决方案，但所有这些都没有奏效。我的适配器：

public class HistoryViewAdapter extends RecyclerView.Adapter<HistoryViewHolder> {

    private ArrayList<ApplicationDataManager> arrayOfHistoryManagerClass;


    public HistoryViewAdapter(ArrayList<ApplicationDataManager> HistoryClassArray) {

        this.arrayOfHistoryManagerClass = HistoryClassArray;

    }


    @Override
    public HistoryViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        View itemView = LayoutInflater.
                from(parent.getContext()).
                inflate(R.layout.history_translate_include, parent, false);

        return new HistoryViewHolder(itemView);
    }

    @Override
    public void onBindViewHolder(HistoryViewHolder holder, int position) {
        ApplicationDataManager managerClass = arrayOfHistoryManagerClass.get(position);
            holder.NonTranslatedWord.setText(managerClass.getNonTranslatedText());
            holder.TranslatedWord.setText(managerClass.GetTranslatedText());
            holder.isFavoret.setChecked(managerClass.GetFavoredStat());

    }

    @Override
    public int getItemCount() {
        return arrayOfHistoryManagerClass.size();
    }



}

我的ViewHolder（我试过FindViewByid而不是Butterknife，但是它给出了相同的异常）：

public class HistoryViewHolder extends RecyclerView.ViewHolder {
    // Defining a TextView
    @InjectView(R.id.translated_word)
    protected  TextView TranslatedWord;
    // Defining a TextView
    @InjectView(R.id.non_translated_word)
    protected  TextView NonTranslatedWord;
    @InjectView(R.id.history_checkBox)
    protected  CheckBox isFavoret;

    public HistoryViewHolder(View itemView) {
        super(itemView);
        //injecting views
        ButterKnife.inject(itemView);

    }
}

最后MyFragment：

public class HistoryFragment extends Fragment {
    @InjectView(R.id.history_recyclerview)
    RecyclerView historyRecycler;
    HistoryViewAdapter historyViewAdapter;
    ArrayList<ApplicationDataManager> listDataManager;
    LinearLayoutManager layoutManager;
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {

        View rootView = inflater.inflate(R.layout.history_translate_include, container, false);
        ButterKnife.inject(this, rootView);

        layoutManager = new LinearLayoutManager(getActivity());
        layoutManager.setOrientation(LinearLayoutManager.VERTICAL);
        historyRecycler.setLayoutManager(layoutManager);

        listDataManager = new ArrayList<ApplicationDataManager>();
        listDataManager.add(new ApplicationDataManager("Test","Test",true,"Engilsh","arabic"));
        listDataManager.add(new ApplicationDataManager("Test","Test",false,"Engilsh","arabic"));

        historyViewAdapter = new HistoryViewAdapter(listDataManager);

        historyRecycler.setAdapter(historyViewAdapter);


        return rootView;
    }
}

更新：我的logcat：

  java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setText(java.lang.CharSequence)' on a null object reference
            at list.adapter.HistoryViewAdapter.onBindViewHolder(HistoryViewAdapter.java:42)
            at list.adapter.HistoryViewAdapter.onBindViewHolder(HistoryViewAdapter.java:18)
            at android.support.v7.widget.RecyclerView$Adapter.bindViewHolder(RecyclerView.java:4138)
            at android.support.v7.widget.RecyclerView$Recycler.getViewForPosition(RecyclerView.java:3448)
            at android.support.v7.widget.RecyclerView$Recycler.getViewForPosition(RecyclerView.java:3340)
            at android.support.v7.widget.LinearLayoutManager$LayoutState.next(LinearLayoutManager.java:1810)
            at android.support.v7.widget.LinearLayoutManager.layoutChunk(LinearLayoutManager.java:1306)
            at android.support.v7.widget.LinearLayoutManager.fill(LinearLayoutManager.java:1269)
            at android.support.v7.widget.LinearLayoutManager.onLayoutChildren(LinearLayoutManager.java:523)
            at android.support.v7.widget.RecyclerView.dispatchLayout(RecyclerView.java:1988)
            at android.support.v7.widget.RecyclerView.onLayout(RecyclerView.java:2237)
            at android.view.View.layout(View.java:15631)
            at android.view.ViewGroup.layout(ViewGroup.java:4966)
            at android.widget.FrameLayout.layoutChildren(FrameLayout.java:573)
            at android.widget.FrameLayout.onLayout(FrameLayout.java:508)
            at android.view.View.layout(View.java:15631)
            at android.view.ViewGroup.layout(ViewGroup.java:4966)
            at android.widget.FrameLayout.layoutChildren(FrameLayout.java:573)
            at android.widget.FrameLayout.onLayout(FrameLayout.java:508)
            at android.view.View.layout(View.java:15631)
            at android.view.ViewGroup.layout(ViewGroup.java:4966)
            at android.widget.RelativeLayout.onLayout(RelativeLayout.java:1076)
            at android.view.View.layout(View.java:15631)
            at android.view.ViewGroup.layout(ViewGroup.java:4966)
            at android.widget.FrameLayout.layoutChildren(FrameLayout.java:573)
            at android.widget.FrameLayout.onLayout(FrameLayout.java:508)
            at android.widget.ScrollView.onLayout(ScrollView.java:1531)
            at android.view.View.layout(View.java:15631)
            at android.view.ViewGroup.layout(ViewGroup.java:4966)
            at android.widget.RelativeLayout.onLayout(RelativeLayout.java:1076)
            at android.view.View.layout(View.java:15631)
            at android.view.ViewGroup.layout(ViewGroup.java:4966)
            at android.widget.FrameLayout.layoutChildren(FrameLayout.java:573)
            at android.widget.FrameLayout.onLayout(FrameLayout.java:508)
            at android.view.View.layout(View.java:15631)
            at android.view.ViewGroup.layout(ViewGroup.java:4966)
            at android.widget.FrameLayout.layoutChildren(FrameLayout.java:573)
            at android.widget.FrameLayout.onLayout(FrameLayout.java:508)
            at android.view.View.layout(View.java:15631)
            at android.view.ViewGroup.layout(ViewGroup.java:4966)
            at android.widget.FrameLayout.layoutChildren(FrameLayout.java:573)
            at android.widget.FrameLayout.onLayout(FrameLayout.java:508)
            at android.view.View.layout(View.java:15631)
            at android.view.ViewGroup.layout(ViewGroup.java:4966)
            at android.widget.FrameLayout.layoutChildren(FrameLayout.java:573)
            at android.widget.FrameLayout.onLayout(FrameLayout.java:508)
            at android.view.View.layout(View.java:15631)
            at android.view.ViewGroup.layout(ViewGroup.java:4966)
            at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1705)
            at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1559)
            at android.widget.LinearLayout.onLayout(LinearLayout.java:1468)
            at android.view.View.layout(View.java:15631)
            at android.view.ViewGroup.layout(ViewGroup.java:4966)
            at android.widget.FrameLayout.layoutChildren(FrameLayout.java:573)
            at android.widget.FrameLayout.onLayout(FrameLayout.java:508)
            at android.view.View.layout(View.java:15631)
            at android.view.ViewGroup.layout(ViewGroup.java:4966)
            at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1705)
            at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1559)
            at android.widget.LinearLayout.onLayout(LinearLayout.j

我的history_translate_include.xml：

<?xml version="1.0" encoding="utf-8"?>
<ScrollView xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="wrap_content">

    <RelativeLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content">

        <TextView
            android:id="@+id/history_textview"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_alignParentLeft="true"
            android:layout_alignParentStart="true"
            android:layout_alignParentTop="true"
            android:layout_marginLeft="10dp"
            android:text="@string/translate_history"
            android:textAppearance="?android:attr/textAppearanceLarge" />

        <RecyclerView

            android:id="@+id/history_recyclerview"
            android:layout_width="match_parent"
            android:layout_height="400dp"
            android:layout_alignLeft="@+id/history_textview"
            android:layout_alignParentEnd="true"
            android:layout_alignParentRight="true"
            android:layout_alignStart="@+id/history_textview"
            android:layout_below="@+id/history_textview"
            android:layout_marginRight="10dp"
            android:layout_marginTop="10dp"

            />
    </RelativeLayout>

</ScrollView>

提前致谢

Answer 1

你使用错误的ButterKnife注入方法。

使用下面的HistoryViewHolder构造函数：

public HistoryViewHolder(View itemView) {
    super(itemView);
    //This line is important
    ButterKnife.inject(this,itemView);

}

而不是

public HistoryViewHolder(View itemView) {
    super(itemView);
    //injecting views
    ButterKnife.inject(itemView);

}

如果要为包含这些视图的对象注入一些视图但不是Fragment Activity或View，则必须调用方法：

 ButterKnife.inject(Object,View);

此外，您在onCreateViewHolder方法中使用history_translate_include，您应该使用包含这些ID的视图的单个项目布局：translated_word, non_translated_word, history_checkBox

@Override
public HistoryViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {

    View itemView = LayoutInflater.
            from(parent.getContext()).
            inflate(R.layout.layout_for_single_item, parent, false);

    return new HistoryViewHolder(itemView);
}

视图在RecyclerView Adapter中的onBindViewHolder中返回NullPointerException

1 个答案: