Question

我尝试创建一个水平的recyclerView，但是recyclerView找不到上下文，这是我的Fragmnet代码：

 public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    this.context =context;
    if (getArguments() != null) {
        mParam1 = getArguments().getString(ARG_PARAM1);
        mParam2 = getArguments().getString(ARG_PARAM2);

    }
}

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
    // Inflate the layout for this fragment
    ArrayList<CategoryModel> categoryModels = null;

    RecyclerView recyclerView = container.findViewById(R.id.category_recycler);
   // recyclerView.setHasFixedSize(true);
    CategoryAdapter adapter = new CategoryAdapter(context,CategoryData.getCategory());
    recyclerView.setAdapter(adapter);
    LinearLayoutManager layoutManager = new LinearLayoutManager(getActivity());
    layoutManager.setOrientation(LinearLayoutManager.HORIZONTAL);
    recyclerView.setLayoutManager(layoutManager);


    return inflater.inflate(R.layout.main_fragment, container, false);
}

这是Recycler视图适配器代码：

public class CategoryAdapter extends RecyclerView.Adapter<CategoryAdapter.ViewHolder> {
    Context context;
    ArrayList<CategoryModel> categorys;
    public CategoryAdapter(Context context, ArrayList<CategoryModel> categoryModels) {
        this.categorys = categoryModels;
        this.context = context;
    }

    @NonNull

    @Override
    public CategoryAdapter.ViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        View view = LayoutInflater.from(context).inflate(R.layout.product_category,parent,false);
        return new ViewHolder(view);
    }

我还附上了调试结果，请检查图片

Answer 1

要在Context内使用Fragment，请使用getContext()方法。

CategoryAdapter adapter = new CategoryAdapter(getContext(),CategoryData.getCategory());

来自official文档

返回此片段当前与之关联的上下文。

如果您仅使用Context来放大onCreateViewHolder类中CategoryAdapter方法内的视图，则无需在Constructor中传递Context。您可以从Context方法的第一个参数ViewGroup获得onCreateViewHolder。

View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.product_category,parent,false);

Answer 2

在您的onCreate()片段回调中，我看到以下行：

public void onCreate(Bundle savedInstanceState) {
    ...
    this.context =context;
    ...
}

此行不执行任何操作； context方法没有onCreate()参数或类似方法，因此您只是将变量赋值给它自己。由于您的Context context字段没有显式的初始化，因此默认值为null。所以这和写作一样

public void onCreate(Bundle savedInstanceState) {
    ...
    this.context = null;
    ...
}

稍后，在onCreateView()中，您将使用以下行实例化适配器：

CategoryAdapter adapter = new CategoryAdapter(context,CategoryData.getCategory());

由于我上面所说的，这在功能上与

相同

CategoryAdapter adapter = new CategoryAdapter(null, CategoryData.getCategory());

要解决此问题，您需要一些位置来获取一个Context实例。片段通常是“附加”到上下文的，当它们附加后，您可以通过调用getContext()来获取该上下文。肯定会在onActivityCreated()回调中将一个片段附加到上下文，因此您将需要将适配器创建移至该回调，而不是onViewCreated()。

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
    return inflater.inflate(R.layout.main_fragment, container, false);
}

@Override
public void onActivityCreated(Bundle savedInstanceState) {
    super.onActivityCreated(savedInstanceState);

    CategoryAdapter adapter = new CategoryAdapter(getContext(), CategoryData.getCategory());

    LinearLayoutManager layoutManager = new LinearLayoutManager(getActivity());
    layoutManager.setOrientation(LinearLayoutManager.HORIZONTAL);

    RecyclerView recyclerView = getView().findViewById(R.id.category_recycler);
    recyclerView.setAdapter(adapter);
    recyclerView.setLayoutManager(layoutManager);
}

Answer 3

尝试这样：

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup parent, Bundle savedInstanceState) {
            // Defines the xml file for the fragment
            return inflater.inflate(R.layout.main_fragment, parent, false);
    }

    @Override
    public void onViewCreated(View view, Bundle savedInstanceState) {

        // Inflate the layout for this fragment
        ArrayList<CategoryModel> categoryModels = null;

        RecyclerView recyclerView = view.findViewById(R.id.category_recycler);
        // recyclerView.setHasFixedSize(true);
        CategoryAdapter adapter = new CategoryAdapter(getContext(), CategoryData.getCategory());
        LinearLayoutManager layoutManager = new LinearLayoutManager(getActivity());
        layoutManager.setOrientation(LinearLayoutManager.HORIZONTAL);
        recyclerView.setLayoutManager(layoutManager);
        recyclerView.setAdapter(adapter);

    }

RecyclerView无法使用片段

3 个答案: