在 Fragment 中顯示 RecyclerView

Question

我正在 Android Lollipop 中試用新的RecyclerView ，但被卡住了。

我正在嘗試接收一個列表，在一個Fragment ，在圖標的右側有一個圖標和一個TextView 。

我發現了這個關於如何設置RecyclerView 很棒的教程。 我遵循了每一點，只更改了item_layout.xml以滿足我的需要。

該項目構建時沒有任何錯誤，但是當它在我的設備上啟動時，我收到此錯誤：

java.lang.RuntimeException：無法啟動活動 ComponentInfo{com.fredrikaldgard.materialcolors/com.fredikaldgard.materialcolors.MainActivity}：java.lang.NullPointerException：嘗試調用虛擬方法 'void android.support.v7.widget.RecyclerView。空對象引用上的 setLayoutManager(android.support.v7.widget.RecyclerView$LayoutManager)'

我試圖用谷歌搜索這個問題，但我對 Android 開發非常業余。

這是我的MainActivity ：

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    // 1. get a reference to recyclerView
    RecyclerView recyclerView = (RecyclerView) findViewById(R.id.list);

    // 2. set layoutManger
    recyclerView.setLayoutManager(new LinearLayoutManager(this));

    // this is data fro recycler view
    ItemData itemsData[] = { new ItemData("Indigo",R.drawable.circle),
            new ItemData("Red",R.drawable.color_ic_launcher),
            new ItemData("Blue",R.drawable.indigo),
            new ItemData("Green",R.drawable.circle),
            new ItemData("Amber",R.drawable.color_ic_launcher),
            new ItemData("Deep Orange",R.drawable.indigo)};


    // 3. create an adapter
    MyAdapter mAdapter = new MyAdapter(itemsData);
    // 4. set adapter
    recyclerView.setAdapter(mAdapter);
    // 5. set item animator to DefaultAnimator
    recyclerView.setItemAnimator(new DefaultItemAnimator());

還有我的MyAdapter ：

public class MyAdapter extends RecyclerView.Adapter<MyAdapter.ViewHolder> {
private ItemData[] itemsData;

public MyAdapter(ItemData[] itemsData) {
    this.itemsData = itemsData;
}

// Create new views (invoked by the layout manager)
@Override
public MyAdapter.ViewHolder onCreateViewHolder(ViewGroup parent,
                                               int viewType) {
    // create a new view
    View itemLayoutView = LayoutInflater.from(parent.getContext())
            .inflate(R.layout.item_layout, null);

    // create ViewHolder

    ViewHolder viewHolder = new ViewHolder(itemLayoutView);
    return viewHolder;
}

// Replace the contents of a view (invoked by the layout manager)
@Override
public void onBindViewHolder(ViewHolder viewHolder, int position) {

    // - get data from your itemsData at this position
    // - replace the contents of the view with that itemsData

    viewHolder.txtViewTitle.setText(itemsData[position].getTitle());
    viewHolder.imgViewIcon.setImageResource(itemsData[position].getImageUrl());


}

// inner class to hold a reference to each item of RecyclerView
public static class ViewHolder extends RecyclerView.ViewHolder {

    public TextView txtViewTitle;
    public ImageView imgViewIcon;

    public ViewHolder(View itemLayoutView) {
        super(itemLayoutView);
        txtViewTitle = (TextView) itemLayoutView.findViewById(R.id.item_title);
        imgViewIcon = (ImageView) itemLayoutView.findViewById(R.id.item_icon);
    }
}


// Return the size of your itemsData (invoked by the layout manager)
@Override
public int getItemCount() {
    return itemsData.length;
}
}

編輯：這是Fragment

public class ColorsFragment extends Fragment {

    public ColorsFragment(){}

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {

        View rootView = inflater.inflate(R.layout.fragment_colors, container, false);

        return rootView;
    }
}

可能出了什么問題？

Answer 1

這是前一段時間被問到的，但是根據@nacho_zona3 提供的答案以及之前使用片段的經驗，問題是當您嘗試使用findViewById()方法在onCreate()要解決此問題，請移動以下代碼：

// 1. get a reference to recyclerView
RecyclerView recyclerView = (RecyclerView) findViewById(R.id.list);

// 2. set layoutManger
recyclerView.setLayoutManager(new LinearLayoutManager(this));

// this is data from recycler view
ItemData itemsData[] = { new ItemData("Indigo",R.drawable.circle),
        new ItemData("Red",R.drawable.color_ic_launcher),
        new ItemData("Blue",R.drawable.indigo),
        new ItemData("Green",R.drawable.circle),
        new ItemData("Amber",R.drawable.color_ic_launcher),
        new ItemData("Deep Orange",R.drawable.indigo)};


// 3. create an adapter
MyAdapter mAdapter = new MyAdapter(itemsData);
// 4. set adapter
recyclerView.setAdapter(mAdapter);
// 5. set item animator to DefaultAnimator
recyclerView.setItemAnimator(new DefaultItemAnimator()); 

到您片段的onCreateView()調用。 需要少量重構，因為從此方法調用的所有變量和方法都必須是靜態的。 最終代碼應如下所示：

 public class ColorsFragment extends Fragment {

     public ColorsFragment() {}

     @Override
     public View onCreateView(LayoutInflater inflater, ViewGroup container,
         Bundle savedInstanceState) {

         View rootView = inflater.inflate(R.layout.fragment_colors, container, false);
         // 1. get a reference to recyclerView
         RecyclerView recyclerView = (RecyclerView) rootView.findViewById(R.id.list);

         // 2. set layoutManger
         recyclerView.setLayoutManager(new LinearLayoutManager(getActivity()));

         // this is data from recycler view
         ItemData itemsData[] = {
             new ItemData("Indigo", R.drawable.circle),
                 new ItemData("Red", R.drawable.color_ic_launcher),
                 new ItemData("Blue", R.drawable.indigo),
                 new ItemData("Green", R.drawable.circle),
                 new ItemData("Amber", R.drawable.color_ic_launcher),
                 new ItemData("Deep Orange", R.drawable.indigo)
         };


         // 3. create an adapter
         MyAdapter mAdapter = new MyAdapter(itemsData);
         // 4. set adapter
         recyclerView.setAdapter(mAdapter);
         // 5. set item animator to DefaultAnimator
         recyclerView.setItemAnimator(new DefaultItemAnimator());

         return rootView;
     }
 }

所以這里的主要事情是在任何你調用findViewById()你都需要使用rootView.findViewById()

Answer 2

在使用該視圖膨脹核心視圖后，您應該在Fragment檢索RecyclerView 。 也許它找不到您的回收站，因為它不是 Activity 的一部分

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
    final View view = inflater.inflate(R.layout.fragment_artist_tracks, container, false);
    final FragmentActivity c = getActivity();
    final RecyclerView recyclerView = (RecyclerView) view.findViewById(R.id.recyclerView);
    LinearLayoutManager layoutManager = new LinearLayoutManager(c);
    recyclerView.setLayoutManager(layoutManager);

    new Thread(new Runnable() {
        @Override
        public void run() {
            final RecyclerAdapter adapter = new RecyclerAdapter(c);
            c.runOnUiThread(new Runnable() {
                @Override
                public void run() {
                    recyclerView.setAdapter(adapter);
                }
            });
        }
    }).start();

    return view;
}

Answer 3

確保您有正確的布局，並且 RecyclerView id 在布局內。 否則，您將收到此錯誤。 我遇到了同樣的問題，然后我注意到布局錯誤。

    public class ColorsFragment extends Fragment {

         public ColorsFragment() {}

         @Override
         public View onCreateView(LayoutInflater inflater, ViewGroup container,
             Bundle savedInstanceState) {

==> make sure you are getting the correct layout here. R.layout...

             View rootView = inflater.inflate(R.layout.fragment_colors, container, false); 

Answer 4

我遇到了同樣的問題。 並在我使用此代碼調用上下文時得到了解決方案。 我使用網格布局。 如果你使用另一個你可以改變。

   recyclerView.setLayoutManager(new GridLayoutManager(getActivity(),1));

如果你有適配器要設置。 所以你可以遵循這個。 只需調用 getContext

  adapter = new Adapter(getContext(), myModelList);

如果您要顯示 Toast，請使用上面相同的內容

   Toast.makeText(getContext(), "Error in "+e, Toast.LENGTH_SHORT).show();

希望這會奏效。

快樂編碼