Implement Android bottom sheet in my recyclerview adapter class

I want to implement android bottom sheet in Onlongclick of my Recyclerview Adapter class, but am trying to press long click on my recyclerview item its got crashed.

     public class AddAtendanceAdapter extends      
        RecyclerView.Adapter<AddAtendanceAdapter.AttendanceViewHolder> {
        public List<Details> dAttendance = Collections.emptyList();

        private LayoutInflater inflater;
        private static Context context;

        private View v;




        public AddAtendanceAdapter(Context context, List<Details> dAttendance) {
            this.dAttendance = dAttendance;
            this.context = context;
            inflater = LayoutInflater.from(context);
        }

        @Override
        public AttendanceViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
            View v = LayoutInflater.from(parent.getContext()).inflate(R.layout.student_item_row,
    parent, false);
            AttendanceViewHolder pvh = new AttendanceViewHolder(v);
            return pvh;
        }

        @Override
        public void onBindViewHolder(AttendanceViewHolder holder, int postions) {
            Details details = dAttendance.get(postions);
            holder.StudentsName.setText(details.getStudentName());
            Glide.with(context)
                    .load(details.getStudentImage())
                    .into(holder.stdImg);

        }

        @Override
        public int getItemCount() {
            if (dAttendance != null) {
                return dAttendance.size();
            }
            return 0;
        }


        @Override
        public void onAttachedToRecyclerView(RecyclerView recyclerView) {
            super.onAttachedToRecyclerView(recyclerView);
        }

        public static class AttendanceViewHolder extends RecyclerView.ViewHolder {



            TextView StudentsName;
            CircleImageView stdImg;
            private  Activity activity;
            AttendanceViewHolder(View itemView) {
                super(itemView);
                StudentsName = (TextView) itemView.findViewById(R.id.txtStdName);
                stdImg = (CircleImageView) itemView.findViewById(R.id.stdImg);
                itemView.setOnLongClickListener(new View.OnLongClickListener() {
                    @Override
                    public boolean onLongClick(View v) {
                        Log.d("juu","hhh");
                        openBottomSheet(v);

                        return false;
                    }
                });


            }
            private  void openBottomSheet(View v) {
           //View view = activity.getLayoutInflater ().inflate (R.layout.bottom_sheet, null);
               // View view = inflater.inflate( R.layout.bottom_sheet, null );

                LayoutInflater inflater = (LayoutInflater) context.getSystemService( Context.LAYOUT_INFLATER_SERVICE );
            View view = inflater.inflate (R.layout.bottom_sheet, null);
                TextView txtBackup = (TextView)view.findViewById(R.id.txt_backup);
                TextView txtDetail = (TextView)view.findViewById(R.id.txt_detail);
                TextView txtOpen = (TextView)view.findViewById(R.id.txt_open);
                final TextView txtUninstall = (TextView)view.findViewById( R.id.txt_uninstall);

                final Dialog mBottomSheetDialog = new Dialog (context, R.style.MaterialDialogSheet);
                mBottomSheetDialog.setContentView (view);
                mBottomSheetDialog.setCancelable (true);
                mBottomSheetDialog.getWindow ().setLayout (LinearLayout.LayoutParams.MATCH_PARENT,
    LinearLayout.LayoutParams.WRAP_CONTENT);
                mBottomSheetDialog.getWindow ().setGravity (Gravity.BOTTOM);
                mBottomSheetDialog.show ();


                txtBackup.setOnClickListener(new View.OnClickListener() {

                    @Override
                    public void onClick(View v) {
                        Toast.makeText(context,"Clicked Backup",Toast.LENGTH_SHORT).show();
                        mBottomSheetDialog.dismiss();
                    }
                });

                txtDetail.setOnClickListener(new View.OnClickListener() {

                    @Override
                    public void onClick(View v) {
                        Toast.makeText(context,"Clicked Detail",Toast.LENGTH_SHORT).show();
                        mBottomSheetDialog.dismiss();
                    }
                });

                txtOpen.setOnClickListener(new View.OnClickListener() {

                    @Override
                    public void onClick(View v) {
                        Toast.makeText(context,"Clicked Open",Toast.LENGTH_SHORT).show();
                        mBottomSheetDialog.dismiss();
                    }
                });

                txtUninstall.setOnClickListener(new View.OnClickListener() {

                    @Override
                    public void onClick(View v) {
                        Toast.makeText(context,"Clicked Uninstall",Toast.LENGTH_SHORT).show();
                        mBottomSheetDialog.dismiss();
                    }
                });
            }

        }

}

my log cat is

android.view.WindowManager$BadTokenException: Unable to add window -- token null is not for an application at android.view.ViewRootImpl.setView(ViewRootImpl.java:583) at android.view.WindowManagerGlobal.addView(WindowManagerGlobal.java:310) at android.view.WindowManagerImpl.addView(WindowManagerImpl.java:85) at android.app.Dialog.show(Dialog.java:319) at in.edsys.teacherapp.adapters.AddAtendanceAdapter$AttendanceViewHolder.openBottomSheet(AddAtendanceAdapter.java:119) at in.edsys.teacherapp.adapters.AddAtendanceAdapter$AttendanceViewHolder.access$000(AddAtendanceAdapter.java:80) at in.edsys.teacherapp.adapters.AddAtendanceAdapter$AttendanceViewHolder$1.onLongClick(AddAtendanceAdapter.java:95)