问当活动开始使用Linearlayoutmanager时，滚动Recycleview到顶部位置

EN

llm.setReverseLayout(true);

         rv.setHasFixedSize(true);
         LinearLayoutManager llm = new LinearLayoutManager(this);
         llm.setReverseLayout(true);
         rv.setLayoutManager(llm);
         llm.scrollToPositionWithOffset(0, 0);
         rv.setAdapter(staggeredBooksAdapter);

public class SubjectBooks extends AppCompatActivity {
    FirebaseAuth fauth;
    String user;
    DatabaseReference dbreference,dbref;
    RecyclerView rv;
    String subject;
    int child_count=0;
    ArrayList<Books> list;
    SubjectBooksAdapter staggeredBooksAdapter;
    ProgressDialog progressDialog;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_subject_books);
        getSupportActionBar().setTitle(getIntent().getStringExtra("subject")+" Area");
        getSupportActionBar().setBackgroundDrawable(
                new ColorDrawable(Color.parseColor("#8abe50")));
     // this.getSupportActionBar().setDisplayHomeAsUpEnabled(true);
     // this.getSupportActionBar().setHomeAsUpIndicator(R.drawable.ic_menu_share);



        fauth = FirebaseAuth.getInstance();
        subject = getIntent().getStringExtra("subject").trim();

        dbreference = FirebaseDatabase.getInstance().getReference("books").child(subject);
        dbreference.keepSynced(true);
        user = fauth.getCurrentUser().getEmail();

        list = new ArrayList<>();
        staggeredBooksAdapter = new SubjectBooksAdapter(list);

        rv = (RecyclerView) findViewById(R.id.recyclerView);

        final ProgressDialog  progressDialog = ProgressDialog.show(this, "Loading...", "Please wait...", true);
        progressDialog.setMessage("Please wait ...");
        progressDialog.setCanceledOnTouchOutside(true);
        progressDialog.show();

        rv.setHasFixedSize(true);
        LinearLayoutManager llm = new LinearLayoutManager(this);
        rv.setLayoutManager(llm);
        rv.setAdapter(staggeredBooksAdapter);

        dbreference.addChildEventListener(new ChildEventListener() {
            @Override
            public void onChildAdded(DataSnapshot dataSnapshot, String s) {

                final Books b1 = dataSnapshot.getValue(Books.class);
              //  Log.e("Value is ",dataSnapshot.getKey()+" "+b1.getBauthor());
                //Log.e("Book"," received");
                if(!user.equals(b1.getSelleremail()) || (user.equals(b1.getSelleremail())) ) {

                    child_count++;
                    list.add(b1);
                    staggeredBooksAdapter.notifyDataSetChanged();
                    progressDialog.dismiss();
                }


   
}

/Solution one
mLayoutManager.scrollToPositionWithOffset(0, 0);
//Solution Two
rv.scrollToPosition(0)
//Solution Three
setStackFromEnd(false)
//Solution Four
Collections.reverse();