java.lang.NullPointerException：使用 RecyclerView.Widget 時出錯

Question

我正在嘗試將音頻文件列表添加到我的片段中。 我還將布局管理器設置為回收站視圖。 我還向 gradle 構建添加了依賴項

這是錯誤：

java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.View androidx.recyclerview.widget.RecyclerView.findViewById(int)' on a null object reference
        at com.example.musicplayer.AllSongs.onCreateView(AllSongs.java:35)
        at androidx.fragment.app.Fragment.performCreateView(Fragment.java:2698)
       

我正在嘗試在我的所有歌曲片段中獲取所有歌曲。 這是我的代碼，它顯示錯誤：

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

        recyclerView = recyclerView.findViewById(R.id.recyclerView);
        recyclerView.setHasFixedSize(true);
        if (!(musicFiles.size() < 1))
        {
            musicAdapter = new MusicAdapter(getContext(),musicFiles);
            recyclerView.setAdapter(musicAdapter);
            recyclerView.setLayoutManager(new LinearLayoutManager(getContext()));
        }
        return inflater.inflate(R.layout.fragment_all_songs_tab, container, false);
    }

Answer 1

嘗試

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

        recyclerView = view.findViewById(R.id.recyclerView);
        recyclerView.setHasFixedSize(true);
        musicFiles = new ArrayList();
        if (!(musicFiles.size() < 1))
        {
            musicAdapter = new MusicAdapter(getContext(),musicFiles);
            recyclerView.setAdapter(musicAdapter);
            recyclerView.setLayoutManager(new LinearLayoutManager(getContext()));
        }

        return view;
    }

Answer 2

您的應用程序在下一行崩潰

 recyclerView.findViewById(R.id.recyclerView);

按照下面做

 onCreateView(.....){
 View v = inflater.inflate(R.layout.fragment_all_songs_tab, container, false);
 recyclerView = v.findViewById(R.id.recyclerView);
 ....
 ....
 return v ;
 }

Answer 3

錯誤已修復這里是解決方案

我做了什么：

早些時候我返回onCreateView function 但是在View我的代碼被修復后，音頻文件列表顯示

 View view = inflater.inflate(R.layout.fragment_all_songs_tab, container, false);

        recyclerView = view.findViewById(R.id.recyclerView);
        recyclerView.setHasFixedSize(true);

            musicAdapter = new MusicAdapter(getContext(), musicFiles);
            recyclerView.setAdapter(musicAdapter);
            recyclerView.setLayoutManager(new LinearLayoutManager(getContext(), RecyclerView.VERTICAL, false));
        musicAdapter.notifyDataSetChanged();

            return view;