在 Fragment 中显示 RecyclerView [英] Display a RecyclerView in Fragment

问题描述

我正在 Android Lollipop 中试用新的 RecyclerView，但卡住了.

I'm trying out the new RecyclerView in Android Lollipop and I'm stuck.

我正在尝试接收一个列表，其中包含一个图标和一个 TextView 位于图标右侧的 Fragment 中.

I'm trying to receive a list, with an icon and a TextView to the right of the icon, inside a Fragment.

我找到了关于如何设置RecyclerView.我遵循了每一点，只更改了 item_layout.xml 以满足我的需要.

I found this great tutorial on how to set up a RecyclerView. I have followed every point and only changed the item_layout.xml to fit my needs.

项目构建时没有任何错误，但当它在我的设备上启动时，我收到此错误:

The project builds without any errors but when it launches on my device I'm getting this error:

java.lang.RuntimeException: 无法启动活动 ComponentInfo{com.fredrikaldgard.materialcolors/com.fredrikaldgard.materialcolors.MainActivity}: java.lang.NullPointerException: 尝试调用虚方法 'void android.support.v7.widget.RecyclerView.setLayoutManager(android.support.v7.widget.RecyclerView$LayoutManager)' 在一个空对象引用上

java.lang.RuntimeException: Unable to start activity ComponentInfo{com.fredrikaldgard.materialcolors/com.fredrikaldgard.materialcolors.MainActivity}: 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

我试图用谷歌搜索这个问题，但我对 Android 开发非常业余.

I've tried to google the problem but I'm quite an amateur with Android development.

这是我的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());

还有我的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;
}
}

这是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;
    }
}

可能出了什么问题?

推荐答案

这是前段时间问的，但根据@nacho_zona3 提供的答案，以及之前使用片段的经验，问题是视图没有被在您尝试使用 onCreate() 中的 findViewById() 方法查找它们时创建以解决此问题，移动以下代码:

This was asked some time ago now, but based on the answer that @nacho_zona3 provided, and previous experience with fragments, the issue is that the views have not been created by the time you are trying to find them with the findViewById() method in onCreate() to fix this, move the following code:

// 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() 调用.需要少量重构，因为从此方法调用的所有变量和方法都必须是静态的.最终代码应如下所示:

to your fragment's onCreateView() call. A small amount of refactoring is required because all variables and methods called from this method have to be static. The final code should look like:

 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;
     }
 }

所以这里的主要事情是在任何你调用 findViewById() 的地方你都需要使用 rootView.findViewById()

So the main thing here is that anywhere you call findViewById() you will need to use rootView.findViewById()

这篇关于在 Fragment 中显示 RecyclerView的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！