DialogConfig dialogConfig = new DialogConfig.Builder()
                .enableMultipleSelect(true) // default is false
                .enableFolderSelect(true) // default is false
                .initialDirectory(Environment.getExternalStorageDirectory().getAbsolutePath() + File.separator + "Android") // default is sdcard
                .supportFiles(new SupportFile(".3gpp", R.drawable.ic_audio), new SupportFile(".mp3", 0), new SupportFile(".pdf", R.drawable.ic_pdf)) // default is showing all file types.
                .build();

new FilePickerDialogFragment.Builder()
                .configs(dialogConfig) 
                .onFilesSelected(new FilePickerDialogFragment.OnFilesSelectedListener() {
                    @Override
                    public void onFileSelected(List<File> list) {
                        Log.e(TAG, "total Selected file: " + list.size());
                        for (File file : list) {
                            Log.e(TAG, "Selected file: " + file.getAbsolutePath());
                        }
                    }
                })
                .onFolderLoadListener(new FilePickerDialogFragment.OnFolderLoadListener() {
                    @Override
                    public void onLoadFailed(String path) {
                        //Could not access folder because of user permissions, sdcard is not readable...
                    }
                })
                .build()
                .show(getSupportFragmentManager(), null);

public class MyExampleCustomDialog extends BaseFilePickerDialogFragment {
    @NonNull
    @Override
    protected int getLayoutId() {
        return R.layout.dialog_custom;
    }

    @NonNull
    @Override
    protected int getRecyclerViewId() {
        return R.id.recyclerview;
    }

    @Nullable
    @Override
    protected int getTextViewCurrentFolderId() {
        return 0;
    }

    @Override
    protected int getToolbarId() {
        return R.id.myToolBar;
    }

    @Nullable
    @Override
    protected int getDoneButtonId() {
        return 0;
    }

    @NonNull
    @Override
    protected int getLayoutRowId() {
        return R.layout.item_row;
    }

    @NonNull
    @Override
    protected int getImageViewIconId() {
        return R.id.ivImage;
    }

    @NonNull
    @Override
    protected int getTextViewNameId() {
        return R.id.tvName;
    }

    @NonNull
    @Override
    protected int getCheckBoxId() {
        return R.id.checkbox;
    }


    @Override
    protected RecyclerView.LayoutManager getInitialLayoutManager() {
        return new GridLayoutManager(getContext(), 3);
    }


    @Override
    protected void initView(View view) {
        super.initView(view);
        toolbar.inflateMenu(R.menu.menu_custom_dialog);
        toolbar.setOnMenuItemClickListener(new Toolbar.OnMenuItemClickListener() {
            @Override
            public boolean onMenuItemClick(MenuItem item) {
                switch (item.getItemId()) {
                    case R.id.actionDone:
                        doneSelecting();//supported function to passed result to listener
                        break;
                    case R.id.actionList:
                        changeLayoutManager(new LinearLayoutManager(getContext(), LinearLayoutManager.VERTICAL, false));
                        break;
                    case R.id.actionGrid:
                        changeLayoutManager(new GridLayoutManager(getContext(), 3));
                        break;
                }

                return false;
            }
        });
    }

    public static MyExampleCustomDialog newInstance(FilePickerDialogFragment.OnFilesSelectedListener onFilesSelectedListener, DialogConfig dialogConfig) {
        MyExampleCustomDialog myExampleCustomDialog = new MyExampleCustomDialog();
        myExampleCustomDialog.onFilesSelectedListener = onFilesSelectedListener;
        myExampleCustomDialog.dialogConfig = dialogConfig;
        return myExampleCustomDialog;
    }
}