對不起，我是一個(gè)新手，在嘗試從手機(jī)的內(nèi)部存儲(chǔ)中檢索所有 mp3 文件時(shí)遇到了一些問題。不知道為什么，但我無法檢索任何文件，即 ArrayList 正在獲取空值這是我來自 PlaylistActivity 的代碼，這里是我檢索 mp3 文件的地方：private static final int RC_READ = 1;private RecyclerView mRecycler;private ArrayList<File> mSongs;private String[] mSongNames;private MyAdapter mAdapter;@Overrideprotected void onCreate(Bundle savedInstanceState) {    super.onCreate(savedInstanceState);    setContentView(R.layout.activity_playlist);    mRecycler=(RecyclerView) findViewById(R.id.recyclerView);    mRecycler.setLayoutManager(new LinearLayoutManager(this));    mRecycler.setHasFixedSize(true);    mSongs=new ArrayList<>();    if (ContextCompat.checkSelfPermission(this, Manifest.permission.READ_EXTERNAL_STORAGE) != PackageManager.PERMISSION_GRANTED){        ActivityCompat.requestPermissions(this, new String[]{Manifest.permission.READ_EXTERNAL_STORAGE}, RC_READ );    }    else {        getSongsPlayList(); }}@Overridepublic void onRequestPermissionsResult(int requestCode, @NonNull String[] permissions, @NonNull int[] grantResults) {    super.onRequestPermissionsResult(requestCode, permissions, grantResults);    if(requestCode== RC_READ && grantResults[0]== PackageManager.PERMISSION_GRANTED){        getSongsPlayList();    }}private void getSongsPlayList(){    Log.d("Music","getSongsPlayList()");    mSongs = findSongs(Environment.getExternalStorageDirectory().getAbsolutePath());    if (mSongs != null) {        mSongNames = new String[mSongs.size()];        for (int i = 0; i < mSongs.size(); i++) {            mSongNames[i] = mSongs.get(i).getName().replace(".mp3", "").replace(".wav", "");            Log.d("Music","Song name:"+mSongNames[i]);        }    } else {        Log.d("Music", "Null");        mSongNames = new String[1];        mSongNames[0] = "Star Boy";    }    mAdapter = new MyAdapter(mSongNames, getApplicationContext());    mRecycler.setAdapter(mAdapter);}