Android教程：从指定文件夹读取PDF文件并在RecyclerView中显示

<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
<uses-permission android:name="android.permission.MANAGE_EXTERNAL_STORAGE" />

<application
    android:requestLegacyExternalStorage="true"
    ...>
</application>

private static final int REQUEST_PERMISSIONS = 123;
private boolean boolean_permission;

private void fn_permission() {
    if ((ContextCompat.checkSelfPermission(getActivity(), Manifest.permission.READ_EXTERNAL_STORAGE) != PackageManager.PERMISSION_GRANTED) ||
            (ContextCompat.checkSelfPermission(getActivity(), Manifest.permission.WRITE_EXTERNAL_STORAGE) != PackageManager.PERMISSION_GRANTED)) {

        if ((ActivityCompat.shouldShowRequestPermissionRationale(getActivity(), android.Manifest.permission.READ_EXTERNAL_STORAGE))) {
            // 可以向用户解释为什么需要此权限
        } else {
            ActivityCompat.requestPermissions(getActivity(), new String[]{android.Manifest.permission.READ_EXTERNAL_STORAGE},
                    REQUEST_PERMISSIONS);
        }

        if ((ActivityCompat.shouldShowRequestPermissionRationale(getActivity(), Manifest.permission.WRITE_EXTERNAL_STORAGE))) {
            // 可以向用户解释为什么需要此权限
        } else {
            ActivityCompat.requestPermissions(getActivity(), new String[]{Manifest.permission.WRITE_EXTERNAL_STORAGE},
                    REQUEST_PERMISSIONS);
        }
    } else {
        boolean_permission = true;
    }
}

@Override
public void onRequestPermissionsResult(int requestCode, String[] permissions, int[] grantResults) {
    super.onRequestPermissionsResult(requestCode, permissions, grantResults);
    if (requestCode == REQUEST_PERMISSIONS) {
        if (grantResults.length > 0 && grantResults[0] == PackageManager.PERMISSION_GRANTED) {
            boolean_permission = true;
            // 权限已授予，可以执行文件操作
        } else {
            // 权限被拒绝，给出提示
            Toast.makeText(getActivity(), "请授予存储权限以访问文件", Toast.LENGTH_SHORT).show();
        }
    }
}

private List<PdfModel> readFilesFromSpecificDir() {
    List<PdfModel> list = new ArrayList<>();

    File filePath = new File(getDefaultStorageLocation());
    File[] fileList = filePath.listFiles();

    if (fileList != null) {
        for (File file : fileList) {
            if (file.isFile() && file.getName().toLowerCase().endsWith(".pdf")) {
                // 创建 PdfModel 对象，并添加到列表中
                PdfModel pdfModel = new PdfModel(file.getName(), "123", 1.12, "pdf", file.getPath());
                list.add(pdfModel);
                Log.e(TAG, "readFilesFromSpecificDir: working list of files are given below ______________________________________________" + file.getName());
            }
        }
    } else {
        Toast.makeText(getActivity(), "List empty...", Toast.LENGTH_SHORT).show();
    }

    return list;
}

public String getDefaultStorageLocation() {
    File dir = new File(Environment.getExternalStorageDirectory().getAbsolutePath(), "/YourFolderName/");
    Log.e(TAG, "getDefaultStorageLocation: __________________________________" + dir);
    if (!dir.exists()) {
        boolean isDirectoryCreated = dir.mkdir();
        if (!isDirectoryCreated) {
            Toast.makeText(getActivity(), "Directory cannot be created", Toast.LENGTH_SHORT).show();
            Log.e("Error", "Directory could not be created");
        }
    }
    return dir.getAbsolutePath() + "/";
}

<androidx.recyclerview.widget.RecyclerView
    android:id="@+id/recycler_view"
    android:layout_width="match_parent"
    android:layout_height="match_parent" />

public class PdfAdapter extends RecyclerView.Adapter<PdfAdapter.ViewHolder> {

    private List<PdfModel> pdfList;

    public PdfAdapter(List<PdfModel> pdfList) {
        this.pdfList = pdfList;
    }

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

    @Override
    public void onBindViewHolder(@NonNull ViewHolder holder, int position) {
        PdfModel pdfModel = pdfList.get(position);
        holder.fileNameTextView.setText(pdfModel.getFileName());
        // 其他数据绑定
    }

    @Override
    public int getItemCount() {
        return pdfList.size();
    }

    public static class ViewHolder extends RecyclerView.ViewHolder {
        TextView fileNameTextView;

        public ViewHolder(@NonNull View itemView) {
            super(itemView);
            fileNameTextView = itemView.findViewById(R.id.file_name_text_view);
            // 其他 View 的初始化
        }
    }
}

RecyclerView recyclerView = findViewById(R.id.recycler_view);
recyclerView.setLayoutManager(new LinearLayoutManager(this));

List<PdfModel> pdfList = readFilesFromSpecificDir();
PdfAdapter adapter = new PdfAdapter(pdfList);
recyclerView.setAdapter(adapter);