与片段一起使用时，“RecyclerView”的初始化方法会使应用程序崩溃

Question

我在我的应用上使用了 recyclerView 来显示来自外部存储的所有文件。在我更改它之前，它在“MainActivity.java”中实现时运行良好。

现在，我希望我的应用有一个“BottomNavigationBar”；为了做到这一点，我使用片段。问题是当我触摸菜单中的特定项目（包含 RecyclerView 的项目）时应用程序崩溃。

我将所有“this”方法更改为“.getActivity()”，但它还是崩溃了。我将其更改为“.getActivity().getApplicationContext()”，但它仍然崩溃。

抱歉，我的电脑不支持硬件加速，所以我无法正确显示错误所在。相反，我已将调试器连接到我连接的手机并设置断点。当应用程序崩溃时，调试器突出显示"RecyclerView recyclerView = getView().findViewById(R.id.recyclerview);" 行。

这是片段代码：

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

    private static final int PERMISSION_REQUEST = 1000;
    private ArrayList<String> mNames = new ArrayList<>();
    public static ArrayList<String> NbFiles = new ArrayList<>();
    public ArrayList<String> PathFiles = new ArrayList<>();

    @Override
    public void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        //Check if we have the permission to read storage
        if (ContextCompat.checkSelfPermission(getActivity(), Manifest.permission.READ_EXTERNAL_STORAGE)
                != PackageManager.PERMISSION_GRANTED) {
            //We don't have the permission, so request it.
            ActivityCompat.requestPermissions(getActivity(), new String[]{Manifest.permission.READ_EXTERNAL_STORAGE}, PERMISSION_REQUEST);
        }
        //We already have permission
        else {
            permissionExists();
        }
    }

    @Override
    public void onActivityResult(int requestCode, int resultCode, Intent data) {
        if (requestCode == PERMISSION_REQUEST) {
            if (resultCode == RESULT_OK) {
                permissionExists();
            } else {
                //handle error
            }
        }
    }

    private void initRecyclerView() {
        RecyclerView recyclerView = getView().findViewById(R.id.recyclerview);
        RecyclerViewAdapter adapter = new RecyclerViewAdapter(mNames, getActivity().getApplicationContext(), (RecyclerViewAdapter.OnNoteListener) this);
        recyclerView.setAdapter(adapter);
        recyclerView.setLayoutManager(new LinearLayoutManager(getActivity().getApplicationContext()));
    }

    private void permissionExists() {
        String path = Environment.getExternalStorageDirectory().toString() + "/Rapture";
        File directory = new File(path);
        boolean success = true;
        if (!directory.exists()) {
            success = directory.mkdirs();
        }
        if (success) {
            File[] arrayFiles = directory.listFiles();
            for (File file : arrayFiles) {
                mNames.add(file.getName());
                PathFiles.add(file.getPath());
                NbFiles.add(file.getName());
            }
        }
        initRecyclerView();
    }
}

[如果您需要更多代码，请告诉我]

我该如何解决这个问题？

Answer 1

RecyclerView recyclerView = getView().findViewById(R.id.recyclerview);

你需要使用onCreateView中膨胀的视图，而不是getView()

所以，

 RecyclerView recyclerView;

    public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        View v = inflater.inflate(R.layout.fragment_records, container, false);
        recyclerView = v.findViewById(R.id.recyclerview);
        return v;
    }

如果需要，您可以在 initRecyclerView() 中填充 RecyclerView（或使其可见，或其他）

Answer 2

把你的代码改成这个-

public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
    View view = inflater.inflate(R.layout.fragment_records, container, false);
    initRecyclerView(view);
    return view;
}



private void initRecyclerView(View view) {
        RecyclerView recyclerView = view.findViewById(R.id.recyclerview);
        RecyclerViewAdapter adapter = new RecyclerViewAdapter(mNames, getActivity().getApplicationContext(), (RecyclerViewAdapter.OnNoteListener) this);
        recyclerView.setAdapter(adapter);
        recyclerView.setLayoutManager(new LinearLayoutManager(getActivity().getApplicationContext()));
    }

Answer 3

试试这个 getActivity()getView() 的实例

RecyclerView recyclerView = getView().findViewById(R.id.recyclerview);  

实例

RecyclerView recyclerView = getActivity().findViewById(R.id.recyclerview);

Answer 4

移动下面的代码来处理权限onActivityCreated

@Override
    public void onActivityCreated(@Nullable Bundle savedInstanceState) {
        super.onActivityCreated(savedInstanceState);
        if (ContextCompat.checkSelfPermission(getActivity(), Manifest.permission.READ_EXTERNAL_STORAGE)
                != PackageManager.PERMISSION_GRANTED) {
            //We don't have the permission, so request it.
            ActivityCompat.requestPermissions(getActivity(), new String[]{Manifest.permission.READ_EXTERNAL_STORAGE}, PERMISSION_REQUEST);
        }
        //We already have permission
        else {
            permissionExists();
        }
    }

在Fragment中，你可以在onViewCreated中初始化你的视图

    // This event is triggered soon after onCreateView().
    // Any view setup should occur here.  E.g., view lookups and attaching view listeners.
    @Override
    public void onViewCreated(View view, Bundle savedInstanceState) {
        // Setup any handles to view objects here
         initRecyclerView(view);
    }

如下更改您的initRecyclerView()，

private void initRecyclerView(View v) {
        RecyclerView recyclerView = v.findViewById(R.id.recyclerview);
        RecyclerViewAdapter adapter = new RecyclerViewAdapter(mNames, getActivity().getApplicationContext(), (RecyclerViewAdapter.OnNoteListener) this);
        recyclerView.setAdapter(adapter);
        recyclerView.setLayoutManager(new LinearLayoutManager(getActivity().getApplicationContext()));
    }

它会显示fragment页面，没有空白，

有关Fragment的生命周期的更多说明，请参阅this

Answer 5

移除 onCreate 方法并将逻辑移到 onCreateView 中

Answer 6

这里的问题是您的 recyclerView 通过调用 getActivity() 进行初始化，但问题是在调用 onActivityCreated() 之前该活动不存在。

所以它崩溃了。将onCreate() 中的所有代码移动到onActivityCreated()，它应该可以正常工作。