Create a simple File Finder Dialog in Android

package org.o7planning.filefinderdialogexample;

import android.os.Environment;
import android.util.Log;

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

public class FileFinder {

    private static final String LOG_TAG_FILE_FINDER = "FileSelector";

    private boolean enableLog;

    public FileFinder(boolean enableLog) {
        this.enableLog = enableLog;
    }

    public List<File> findByKeyword(File rootDir, String keywordFileName) {
        if(keywordFileName==null || keywordFileName.isEmpty())  {
            return new ArrayList<File>();
        }
        String regexFileName = keywordFileName.replace("*", ".*?");

        List<File> resultList = this.listOfFile(rootDir, regexFileName);
        return resultList;
    }

    public List<File> findByRegex(File rootDir, String regexFileName) {

        List<File> resultList = this.listOfFile(rootDir, regexFileName);
        return resultList;
    }

    public List<File> findInSDCardByKeyword(String keywordFileName)  {
        // (Example): /storage/emulated/0
        String sdCardPath = Environment.getExternalStorageDirectory().getAbsolutePath();
        this.log("External Storage Directory: " + sdCardPath);

        File sdCardDir = new File(sdCardPath);
        return this.findByKeyword(sdCardDir, keywordFileName);
    }

    public List<File> findInSDCardByRegex(String regexFileName)  {
        // (Example): /storage/emulated/0
        String sdCardPath = Environment.getExternalStorageDirectory().getAbsolutePath();
        this.log("External Storage Directory: " + sdCardPath);

        File sdCardDir = new File(sdCardPath);
        return this.findByRegex(sdCardDir, regexFileName);
    }

    private List<File> listOfFile(File dir, String regexFileName) {
        Pattern patternFileName = Pattern.compile(regexFileName);

        List<File> resultList = new ArrayList<File>();
        this.listOfFile(dir, patternFileName, resultList);
        return resultList;
    }

    private void listOfFile(File dir, Pattern patternFileName, List<File> resultList) {
        this.log("LIST OF DIR " + dir.getAbsolutePath());
        File[] list = dir.listFiles();

        if(list == null)  {
            this.log("Directory" + dir.getAbsolutePath()+ " has no files");
            return;
        }
        this.log("Directory" + dir.getAbsolutePath()+ " has " + list.length +" direct files");

        for (File file : list) {
            if (file.isDirectory()) {
                if (!new File(file, ".nomedia").exists() && !file.getName().startsWith(".")) {
                    this.log( "IS DIR " + file);
                    listOfFile(file, patternFileName, resultList);
                }
            } else {
                String path = file.getAbsolutePath();
                this.log( "FILE PATH: " + path);

                String fileName = file.getName();
                if(patternFileName.matcher(fileName).find())  {
                    resultList.add(file);
                    this.log( "ADD " + path);
                }
            }
        }
    }

    private void log(String message)  {
        if(enableLog) {
            Log.i(LOG_TAG_FILE_FINDER, message);
        }
    }
}

package org.o7planning.filefinderdialogexample;

import java.io.File;

public interface OnFileSelectListener {
    void onSelect(File file);
}

package org.o7planning.filefinderdialogexample;

import android.app.Dialog;
import android.content.Context;
import android.graphics.Typeface;
import android.util.TypedValue;
import android.view.Gravity;
import android.view.View;
import android.view.ViewGroup;
import android.view.Window;
import android.widget.LinearLayout;
import android.widget.TextView;

import androidx.annotation.NonNull;
import androidx.recyclerview.widget.LinearLayoutManager;
import androidx.recyclerview.widget.RecyclerView;

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

public class ResultDialog extends Dialog {

    public ResultDialog(@NonNull Context context, List<File> resultList, OnFileSelectListener listener) {
        super(context);

        this.requestWindowFeature(Window.FEATURE_NO_TITLE);
        //
        LinearLayout linearLayout = new LinearLayout(this.getContext());
        linearLayout.setLayoutParams(new LinearLayout.LayoutParams(ViewGroup.LayoutParams.WRAP_CONTENT, ViewGroup.LayoutParams.WRAP_CONTENT));
        linearLayout.setOrientation(LinearLayout.VERTICAL);

        int p = convertToPixels(12);
        linearLayout.setPadding(p, p, p, p);
        linearLayout.setGravity(Gravity.CENTER);

        TextView textView = new TextView(this.getContext());
        textView.setLayoutParams(new LinearLayout.LayoutParams(screenWidth(), ViewGroup.LayoutParams.WRAP_CONTENT));
        textView.setGravity(Gravity.CENTER);
        textView.setText("~ Search Result ~");

        RecyclerView recyclerView = new RecyclerView(this.getContext());

        linearLayout.addView(textView);
        linearLayout.addView(recyclerView);

        RecyclerViewAdapter adapter = new RecyclerViewAdapter(this.getContext(), this, listener, resultList);
        recyclerView.setAdapter(adapter);
        LinearLayoutManager layoutManager = new LinearLayoutManager(this.getContext());
        layoutManager.setOrientation(LinearLayoutManager.VERTICAL);
        recyclerView.setLayoutManager(layoutManager);

        //
        // this.getWindow().setBackgroundDrawable(new ColorDrawable(android.graphics.Color.TRANSPARENT));
        //
        this.setContentView(linearLayout);
        this.setCancelable(true);
    }

    private int convertToPixels(int dp) {
        float scale = this.getContext().getResources().getDisplayMetrics().density;
        return (int) (dp * scale + 0.5f);
    }

    private int screenWidth() {
        return this.getContext().getResources().getDisplayMetrics().widthPixels;
    }

    // RecyclerViewAdapter
    private class RecyclerViewAdapter extends RecyclerView.Adapter<RecyclerViewAdapter.ViewHolder> {

        private Context context;

        private List<File> files;
        private OnFileSelectListener listener;
        private Dialog dialog;

        public RecyclerViewAdapter(Context context, Dialog dialog, OnFileSelectListener listener, List<File> files) {
            this.context = context;
            this.files = files;
            this.listener = listener;
            this.dialog = dialog;
        }

        // Create new views (invoked by the layout manager)
        @Override
        public RecyclerViewAdapter.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {

            LinearLayout linearLayout = new LinearLayout(context);
            linearLayout.setOrientation(LinearLayout.VERTICAL);
            TextView txtName = new TextView(context);
            TextView txtPath = new TextView(context);
            txtPath.setTypeface(txtPath.getTypeface(), Typeface.ITALIC);
            txtPath.setTextSize(TypedValue.COMPLEX_UNIT_SP, 11);

            linearLayout.addView(txtName);
            linearLayout.addView(txtPath);

            RecyclerViewAdapter.ViewHolder viewHolder = new RecyclerViewAdapter.ViewHolder(linearLayout);
            return viewHolder;
        }

        // Inner class to hold a reference to each item of RecyclerView
        public class ViewHolder extends RecyclerView.ViewHolder {

            public LinearLayout linearLayout;
            public TextView textViewFileName;
            public TextView textViewPath;

            public ViewHolder(View itemLayoutView) {
                super(itemLayoutView);

                this.linearLayout = (LinearLayout) itemLayoutView;
                this.textViewFileName = (TextView) linearLayout.getChildAt(0);
                this.textViewPath = (TextView) linearLayout.getChildAt(1);
            }
        }


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

        @Override
        public void onBindViewHolder(RecyclerViewAdapter.ViewHolder viewHolder, final int position) {
            final File selectedFile = files.get(position);

            final String path = selectedFile.getAbsolutePath();
            String[] split = path.split("/");
            final String name = split[split.length - 1];

            viewHolder.textViewFileName.setText(name);
            viewHolder.textViewPath.setText(path);

            viewHolder.linearLayout.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View v) {
                    dialog.dismiss();
                    listener.onSelect(selectedFile);
                }
            });
        }
    }
}

package org.o7planning.filefinderdialogexample;

import androidx.appcompat.app.AppCompatActivity;
import androidx.core.app.ActivityCompat;

import android.Manifest;
import android.content.pm.PackageManager;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.CheckBox;
import android.widget.EditText;
import android.widget.Toast;

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

public class MainActivity extends AppCompatActivity {

    private static final int MY_REQUEST_CODE_PERMISSION = 1000;

    private static final String LOG_TAG = "AndroidExample";

    private Button buttonSearch;

    private EditText editTextSearch;
    private CheckBox checkBoxIsRegex;

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

        this.editTextSearch = (EditText) this.findViewById(R.id.editText_search);
        this.checkBoxIsRegex = (CheckBox) this.findViewById(R.id.checkBox_isRegex);

        this.buttonSearch = (Button) this.findViewById(R.id.button_search);

        this.buttonSearch.setOnClickListener(new View.OnClickListener(){

            @Override
            public void onClick(View v) {
                askPermissionAndSearchFile();
            }
        });
    }

    private void askPermissionAndSearchFile()  {
        // With Android Level >= 23, you have to ask the user
        // for permission to access External Storage.
        if (android.os.Build.VERSION.SDK_INT >= android.os.Build.VERSION_CODES.M) { // Level 23

            // Check if we have Call permission
            int permisson = ActivityCompat.checkSelfPermission(this,
                    Manifest.permission.READ_EXTERNAL_STORAGE);

            if (permisson != PackageManager.PERMISSION_GRANTED) {
                // If don't have permission so prompt the user.
                this.requestPermissions(
                        new String[]{Manifest.permission.READ_EXTERNAL_STORAGE},
                        MY_REQUEST_CODE_PERMISSION
                );
                return;
            }
        }
        this.doSearchFile();
    }

    private void doSearchFile()   {
        FileFinder fileSelector = new FileFinder(true);
        String searchText = this.editTextSearch.getText().toString();
        boolean isRegex = this.checkBoxIsRegex.isChecked();

        List<File> resultList = null;
        if(isRegex)  {
            resultList = fileSelector.findInSDCardByRegex(searchText);
        } else {
            resultList = fileSelector.findInSDCardByKeyword(searchText);
        }

        ResultDialog dialog = new ResultDialog(this,  resultList,  new OnFileSelectListener() {
            @Override
            public void onSelect(File file) {
                Toast.makeText(MainActivity.this, "Path: " + file.getAbsolutePath(), Toast.LENGTH_LONG).show();
            }
        });
        dialog.show();
    }

    // When you have the request results
    @Override
    public void onRequestPermissionsResult(int requestCode, String[] permissions, int[] grantResults) {

        super.onRequestPermissionsResult(requestCode, permissions, grantResults);
        //
        switch (requestCode) {
            case MY_REQUEST_CODE_PERMISSION: {

                // Note: If request is cancelled, the result arrays are empty.
                // Permissions granted (CALL_PHONE).
                if (grantResults.length > 0
                        && grantResults[0] == PackageManager.PERMISSION_GRANTED) {

                    Log.i( LOG_TAG,"Permission granted!");
                    Toast.makeText(this, "Permission granted!", Toast.LENGTH_SHORT).show();

                    this.doSearchFile();
                }
                // Cancelled or denied.
                else {
                    Log.i(LOG_TAG,"Permission denied!");
                    Toast.makeText(this, "Permission denied!", Toast.LENGTH_SHORT).show();
                }
                break;
            }
        }
    }


}