问片段中的列表视图不是从firebase填充的，但我可以将数据保存到可能的firebase DB

EN

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
    // Inflate the fragment_dash_board for this fragment
    View rootView = inflater.inflate(R.layout.fragment_dash_board, container, false);
    newsListView = (ListView) rootView.findViewById(R.id.newslist_view);

    dbref = FirebaseDatabase.getInstance().getReference();
    dbOperationsHelper = new DBOperationsHelper(dbref);

    /**
     * SET ADAPTER
     */

     //dbAdapter = new DBAdapter(getActivity().getApplicationContext(),dbOperationsHelper.retrieveNews());
    arrayAdapter = new ArrayAdapter<String>(getActivity(), android.R.layout.simple_list_item_1,dbOperationsHelper.retrieveNews());

    //Toast.makeText(getActivity().getApplicationContext(), "MUST NOT BE EMPTY", Toast.LENGTH_SHORT).show();
     newsListView.setAdapter(dbAdapter);


    return rootView;

}

public class DBOperationsHelper {
DatabaseReference dbref;
Boolean saved;
ArrayList<String> newsArraylist = new ArrayList<>();

public DBOperationsHelper(DatabaseReference db){
    this.dbref = db;
}

public Boolean save(DBModel news){
    if(news == null){
        saved = false;
    }else{
        try {
            dbref.child("DBModel").push().setValue(news);
            saved = true;
        } catch (DatabaseException e) {

            e.printStackTrace();
            saved = false;
        }
    }
    return saved;
}

private void fetchData(DataSnapshot dataSnapshot){
    newsArraylist.clear();
    for(DataSnapshot ds : dataSnapshot.getChildren()){
        String news = ds.getValue(DBModel.class).getNewsHead();
        newsArraylist.add(news);
    }
}

/**
 * RETRIEVE NEWS
 */
public ArrayList<String> retrieveNews(){
   dbref.addChildEventListener(new ChildEventListener() {
       @Override
       public void onChildAdded(DataSnapshot dataSnapshot, String s) {
         fetchData(dataSnapshot);
       }

       @Override
       public void onChildChanged(DataSnapshot dataSnapshot, String s) {
           fetchData(dataSnapshot);
       }

       @Override
       public void onChildRemoved(DataSnapshot dataSnapshot) {

       }

       @Override
       public void onChildMoved(DataSnapshot dataSnapshot, String s) {

       }

       @Override
       public void onCancelled(DatabaseError databaseError) {

       }
   });
    return newsArraylist;
}
}

public class DBModel {
boolean bool;
String name, email, username, pass, newsHead, newsBody;

public void setIsLogin(boolean bl){
    this.bool = bl;

}
public boolean getIsLogin(){
    return this.bool;
}

public void setEmail(String email){
    this.email = email;

}
public String getEmail(){
    return this.email;
}

public void setUsername(String username){
    this.username = username;

}
public String getUsername(){
    return this.username;
}

public void setPass(String pass){
    this.pass = pass;

}
public String getPass(){
    return this.pass;
}

public void setNewsHead(String nws_name){
    this.newsHead = nws_name;

}

public String getNewsHead() {
    return newsHead;
}

public void setNewsBody(String newsBody) {
    this.newsBody = newsBody;
}

public String getNewsBody() {
    return newsBody;
}
}