'在com.示例.pdfreader.主活动.查找Pdf（主活动. java：63）在com.示例.pdfreader.主活动.查找Pdf（主活动. java：67）在com.示例.pdfreader.主活动.查找Pdf（主活动. java：67）在com.示例.pdfreader.主活动.显示Pdf（主活动. java：84）在com.示例. pdfreader.主活动$1.已授予权限（主活动. java：44）
我正在特灵构建PdfReader应用程序，并在ArrayList findpdf（）中;方法，我得到了一些异常，它会导致应用程序中的bug，所以它的消失被crahshed '

package com.example.pdfreader;

import androidx.appcompat.app.AppCompatActivity;
import androidx.recyclerview.widget.GridLayoutManager;
import androidx.recyclerview.widget.RecyclerView;

import android.Manifest;
import android.content.Intent;
import android.os.Bundle;
import android.os.Environment;
import android.widget.Toast;

import com.karumi.dexter.Dexter;
import com.karumi.dexter.PermissionToken;
import com.karumi.dexter.listener.PermissionDeniedResponse;
import com.karumi.dexter.listener.PermissionGrantedResponse;
import com.karumi.dexter.listener.PermissionRequest;
import com.karumi.dexter.listener.single.PermissionListener;

import java.io.File;
import java.util.ArrayList;
import java.util.List;

public class MainActivity extends AppCompatActivity implements OnPdfSelectListner{

    private MainAdapter adapter;
    private List<File> pdfList;
    private RecyclerView recyclerView;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        runtimePermission();

    }

    private void runtimePermission(){
        Dexter.withContext(MainActivity.this).withPermission(Manifest.permission.READ_EXTERNAL_STORAGE)
                .withListener(new PermissionListener() {
                    @Override
                    public void onPermissionGranted(PermissionGrantedResponse permissionGrantedResponse) {
                       displayPdf();
                    }

                    @Override
                    public void onPermissionDenied(PermissionDeniedResponse permissionDeniedResponse) {
                        Toast.makeText(MainActivity.this, "Permission Requried", Toast.LENGTH_SHORT).show();
                    }

                    @Override
                    public void onPermissionRationaleShouldBeShown(PermissionRequest permissionRequest, PermissionToken permissionToken) {
                        permissionToken.continuePermissionRequest();
                    }
                }).check();
    }

    public ArrayList<File> findPdf (File file)
    {
        ArrayList<File> arrayList = new ArrayList<> ();
        File[] files = file.listFiles();
            for (File singleFile :files)
            {
                if (singleFile.isDirectory () && !singleFile.isHidden())
                {
                    arrayList.addAll(findPdf(singleFile));
                }
                else{
                    if(singleFile.getName().endsWith(".pdf")) {
                        arrayList.add(singleFile);
                    }
                }
            }
        return  arrayList;
    }

    public void displayPdf()
    {
        recyclerView = findViewById(R.id.rv);
        recyclerView.setHasFixedSize(true);
        recyclerView.setLayoutManager(new GridLayoutManager(this, 3));
        pdfList = new ArrayList<> ();
        pdfList.addAll(findPdf (Environment.getExternalStorageDirectory()));
        adapter = new MainAdapter(this, pdfList,this);
        recyclerView.setAdapter(adapter);
    }

    @Override
    public void onPdfSelected(File file) {
            startActivity(new Intent(MainActivity.this,PdfActivity.class)
                    .putExtra("paht",file.getAbsolutePath()));

    }
}

Here, is the all code of the MainActivity.java and although on calling the displayPdf(); method in runtimePermission(); is ok or shall we need to modify this functions.