如何强制RecyclerView.Adapter在所有元素上调用onBindViewHolder（）

Question

我有VerticalGridView使用RecyclerView.Adapter来填充元素。我发现如果潜在元素不在视口中，则不会调用onBindViewHolder()方法。不幸的是，这导致来自不同方法的NullPointerException因为我在TextView方法中捕获onBindViewHolder()引用并将其传递给外部变量以供稍后操作。

@Override
public void onBindViewHolder(RecyclerView.ViewHolder holder, int position) {
    final ViewHolder viewHolder = (ViewHolder) holder;
    viewHolder.txtCategoryName.setText(categories.get(position).getStrCategory());
    categories.get(position).setTxtViewReference(viewHolder.txtCategoryDefectTotal);
    viewHolder.categoryBoxRoot.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            for(CategoryListItem catItem : categories){
                if(catItem.getStrCategory().equals(viewHolder.txtCategoryName.getText())){
                    int index = Defects.getInstance().getCategories().indexOf(catItem) + 1;
                    MainInterface.grids.get(index).bringToFront();
                    MainInterface.grids.get(index).setVisibility(View.VISIBLE);
                    for(VerticalGridView grid : MainInterface.grids){
                        int gridIndex = MainInterface.grids.indexOf(grid);
                        if(gridIndex != index){
                            grid.setVisibility(View.INVISIBLE);
                        }
                    }
                    break;
                }
            }

        }
    });

根据我的理解，在TextView对象被实例化时会创建对Viewholder的引用。

public class ViewHolder extends RecyclerView.ViewHolder {

    public TextView txtCategoryName;
    public TextView txtCategoryDefectTotal;
    public View categoryBoxRoot;

    public ViewHolder(View itemView) {
        super(itemView);
        txtCategoryName = (TextView) itemView.findViewById(R.id.textViewCategoryName);
        txtCategoryDefectTotal = (TextView) itemView.findViewById(R.id.textViewCategoryTotalDefects);
        categoryBoxRoot = itemView.findViewById(R.id.root_category_box);
    }
}

在onBindViewHolder()实例化时，是否有办法强制Adapter在所有元素上调用？

我尝试了here建议但没有取得任何成功。

我了解强制onBindViewHolder()所有元素都会对whole purpose of the RecycleView.Adapter产生影响。因此，我对如何捕获TextView引用的任何其他建议持开放态度。

作为此问题的临时修复，我可以在生成NullPointerException的方法周围使用try catch块。但是，我担心缺乏参考意味着我将来可能会引入错误。

Answer 1

解决此问题的最简单方法是向下滚动到网格底部，然后返回到顶部。这不能在onCreate()方法中完成，因为此时网格在技术上不可见。相反，它应该在活动的onResume()方法中调用。

@Override
public void onResume(){
    super.onResume();
    VerticalGridView defectGrid = grids.get(0);
    RecyclerView.Adapter adapter = defectGrid.getAdapter();
    defectGrid.smoothScrollToPosition(adapter.getItemCount()-1);
    defectGrid.smoothScrollToPosition(0);
}

这是一个很好的尝试解决方案，但不幸的是它仍然无效。虽然它确实得到了使方法有效的参考，但它不一定有正确的参考。我发现引用可以最终指向不同的TextView，因为RecycleView.Adapter重用视图在不同的区域显示它们。

解决方案：

Mark Keen说他使用notifyDataSetChanged()时是对的。我通过修复我的onBindViewHolder()方法使其工作正常。

@Override
public void onBindViewHolder(RecyclerView.ViewHolder holder, int position) {
    final ViewHolder viewHolder = (ViewHolder) holder;
    viewHolder.txtCategoryName.setText(categories.get(position).getStrCategory());
    viewHolder.txtCategoryDefectTotal.setText(String.valueOf(categories.get(position).getTotalDefectsInCategory()));
}

我还更改了我的数据对象，因此它保存了一个int值，而不是对TextView的引用，因为上面证明了引用无效。最后，当我按下自定义后退按钮时，我添加了对Adapter的调用。

grids.get(0).getAdapter().notifyDataSetChanged();

谢谢大家的贡献！

Answer 2

只需像这样重置Adapter

RecyclerView.Adapter adapter = recList.getAdapter();
recList.setAdapter(null);
recList.setAdapter(adapter);

recList应该是RecyclerView。

Answer 3

了解流程

public class ThemeGridAdapter extends RecyclerView.Adapter<ThemeGridAdapter.ViewHolder> {
    private OnItemClickedListener listener;
    private List<Theme> mDataset;

    public static class ViewHolder extends RecyclerView.ViewHolder {
        public TextView title;
        public TextView subtitle;
        //        public SimpleDraweeView image;
        public ImageView img;
        public ViewGroup container;

        public ViewHolder(RelativeLayout v) {
            super(v);
            container = v;
            title = (TextView) v.findViewById(R.id.theme_name_text);
            subtitle = (TextView) v.findViewById(R.id.theme_name_type);
//            image = (SimpleDraweeView) v.findViewById(R.id.cell_img);
            img = (ImageView) v.findViewById(R.id.cell_img);
        }
    }

    public ThemeGridAdapter(List<Theme> dataset) {
        mDataset = dataset;
    }

    @Override
    public ThemeGridAdapter.ViewHolder onCreateViewHolder(ViewGroup parent,
                                                          int viewType) {
        RelativeLayout v = (RelativeLayout) LayoutInflater.from(parent.getContext())
                .inflate(R.layout.cell, parent, false);
        return new ViewHolder(v);
    }

    @Override
    public void onBindViewHolder(final ViewHolder holder, final int position) {
        holder.title.setText(mDataset.get(position).getTitle());
        holder.subtitle.setText(mDataset.get(position).getAuthor());
//        Uri uri = Uri.parse(mDataset.get(position).getUrl());
        holder.img.setImageResource(mDataset.get(position).getImage());
//        holder.image.setImageURI(uri);
        holder.container.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                if (listener != null)
                    listener.onItemClicked(holder.getAdapterPosition());
            }
        });

    }

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

    public void setListener(OnItemClickedListener listener) {
        this.listener = listener;
    }
}

Answer 4

检查绑定视图的样式

  public class CrimeListFragment extends Fragment {


    private static final String SAVED_SUBTITLE_VISIBLE = "subtitle";

    private static final int REQUEST_CRIME = 1;

    private RecyclerView mRecyclerView;
    private CrimeAdapter mCrimeAdapter;

    private boolean mSubtitleVisible;

    @Override
    public void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setHasOptionsMenu(true);
    }

    @Nullable
    @Override
    public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.fragment_crime_list, container, false);

        mRecyclerView = (RecyclerView) view.findViewById(R.id.crime_recycler_view);
        mRecyclerView.setLayoutManager(new LinearLayoutManager(getActivity()));

        if (savedInstanceState != null){
            mSubtitleVisible = savedInstanceState.getBoolean(SAVED_SUBTITLE_VISIBLE);
        }
        updateUI();


        return view;
    }

    private void updateUI() {

        CrimeLab crimeLab = CrimeLab.get(getActivity());
        List<Crime> crimes = crimeLab.getCrimes();

        if (mCrimeAdapter == null) {
            mCrimeAdapter = new CrimeAdapter(crimes);
            mRecyclerView.setAdapter(mCrimeAdapter);
        } else {
            mCrimeAdapter.setCrimes(crimes);
            mCrimeAdapter.notifyDataSetChanged();
        }
        updateSubtitle();
    }

    private class CrimeHolder extends RecyclerView.ViewHolder implements View.OnClickListener {

        private TextView mTitleTextView;
        private TextView mDateTextView;
        private CheckBox mSolvedCheckBox;
        private Crime mCrime;


        public CrimeHolder(View itemView) {
            super(itemView);

            itemView.setOnClickListener(this);

            mTitleTextView = (TextView) itemView.findViewById(R.id.list_item_crime_title_text_view);
            mDateTextView = (TextView) itemView.findViewById(R.id.list_item_crime_date_text_view);
            mSolvedCheckBox = (CheckBox) itemView.findViewById(R.id.list_item_crime_solved_checkbox);

        }

        public void bindCrime(Crime crime) {

            mCrime = crime;

            mTitleTextView.setText(mCrime.getTitile());
            mDateTextView.setText(mCrime.getDate().toString());
            mSolvedCheckBox.setChecked(mCrime.isSolved());
        }

        @Override
        public void onClick(View v) {

            /*Toast.makeText(getActivity(),mCrime.getTitile() + "clicked!", Toast.LENGTH_SHORT).show();*/

            /*Intent for calling activity from fragment*/
           /* Intent intent = new Intent(getActivity(), CrimeActivity.class);*/
            /*Intent intent = CrimeActivity.newIntent(getActivity(),mCrime.getId());*/
            Intent intent = CrimePagerActivity.newIntent(getActivity(), mCrime.getId());
            /*startActivityForResult(intent,REQUEST_CRIME);*/
            startActivity(intent);
        }
    }

    private class CrimeAdapter extends RecyclerView.Adapter<CrimeHolder> {

        private List<Crime> mCrimes;

        public CrimeAdapter(List<Crime> crimes) {

            mCrimes = crimes;
        }

        @Override
        public CrimeHolder onCreateViewHolder(ViewGroup parent, int viewType) {
            LayoutInflater layoutInflater = LayoutInflater.from(getActivity());

            View view = layoutInflater.inflate(R.layout.list_item_crime, parent, false);
            return new CrimeHolder(view);

        }

        @Override
        public void onBindViewHolder(CrimeHolder holder, int position) {

            Crime crime = mCrimes.get(position);
            /*holder.mTextView.setText(crime.getTitile());*/
            holder.bindCrime(crime);

        }

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

        public void setCrimes(List<Crime> crimes) {

            mCrimes = crimes;
        }
    }


    @Override
    public void onResume() {
        super.onResume();
        updateUI();
    }


    @Override
    public void onActivityResult(int requestCode, int resultCode, Intent data) {
        if (requestCode == REQUEST_CRIME) {

        }
    }

    @Override
    public void onCreateOptionsMenu(Menu menu, MenuInflater inflater) {
        super.onCreateOptionsMenu(menu, inflater);
        inflater.inflate(R.menu.fragment_crime_list, menu);

        MenuItem subtitleItem = menu.findItem(R.id.menu_item_show_subtitle);
        if (mSubtitleVisible){
            subtitleItem.setTitle(R.string.hide_subtitle);
        }else {
            subtitleItem.setTitle(R.string.show_subtitle);
        }
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {

        switch (item.getItemId()) {

            case R.id.menu_item_new_crime:

                Crime crime = new Crime();
                CrimeLab.get(getActivity()).addCrime(crime);
                Intent intent = CrimePagerActivity.newIntent(getActivity(), crime.getId());
                startActivity(intent);
                return true;

            case R.id.menu_item_show_subtitle:

                mSubtitleVisible = !mSubtitleVisible;
                getActivity().invalidateOptionsMenu();
                updateSubtitle();
                return true;

            default:
                return super.onOptionsItemSelected(item);
        }
    }

    private void updateSubtitle(){

        CrimeLab crimeLab = CrimeLab.get(getActivity());
        int crimeCount = crimeLab.getCrimes().size();

        String subtitle = getString(R.string.subtitle_format,crimeCount);
        if (!mSubtitleVisible){

            subtitle  = null;
        }
        AppCompatActivity appCompatActivity = (AppCompatActivity)getActivity();
        appCompatActivity.getSupportActionBar().setSubtitle(subtitle);

    }

    @Override
    public void onSaveInstanceState(Bundle outState) {
        super.onSaveInstanceState(outState);
        outState.putBoolean(SAVED_SUBTITLE_VISIBLE,mSubtitleVisible);
    }
}

Answer 5

这对我有用，并强制叫git fetch origin otherBranch:master

onBindViewHolder()

Answer 6

将您的 RecyclerView 包裹在一个 NestedScrollView 中，这将强制提前绑定所有项目。

<androidx.core.widget.NestedScrollView
    android:id="@+id/container"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <androidx.recyclerview.widget.RecyclerView
        android:id="@+id/rvGrid"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:nestedScrollingEnabled="false" />
</androidx.core.widget.NestedScrollView>