如何在Firebase实时更新Android中的列表视图

Question

我在应用程序中更新我的好友列表(mListView)视图时遇到了一些问题，它似乎只在启动时更新。我知道这是一个更新函数的问题，但我不知道该使用什么。

(我对Firebase和Android还比较新，还在学习中。)

以下是代码：

private ListView mListView;
private ArrayList<String> mFriends;

private List<User> mUserList;

private UserListAdapter mAdapter;

@Nullable
@Override
public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
    View view = inflater.inflate(R.layout.fragment_profile_friends, container, false);
    mSearchParam = (EditText) view.findViewById(R.id.searchFriends);
    mListView = (ListView) view.findViewById(R.id.lvProfileFriends);
    mPhotos = new ArrayList<>();
    mUserList = new ArrayList<>();
    mFriends = new ArrayList<>();



    DisplayFriends();

    return view;
}

private void DisplayFriends(){
    getFriends();
}


private void updateUsersList(){
    Log.d(TAG, "updateUsersList: updating users list");

    mAdapter = new UserListAdapter(getActivity(), R.layout.layout_user_listitem, mUserList);

    mListView.setAdapter(mAdapter);

    mListView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
        @Override
        public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
            Log.d(TAG, "onItemClick: selected user: " + mUserList.get(position).toString());

            //navigate to profile activity
            Intent intent = new Intent(getActivity(), ViewProfileFragment.class);
            intent.putExtra(getString(R.string.calling_activity), getString(R.string.fragment_profile));
            intent.putExtra(getString(R.string.intent_user), mUserList.get(position));
            startActivity(intent);
        }
    });
}

private void updateFriendsList(){
    Log.d(TAG, "getPhotos: getting Friend(s)");
    DatabaseReference reference = FirebaseDatabase.getInstance().getReference();
    for(int i = 0; i < mFriends.size(); i++){
        final int count = i;
        Query query = reference
                .child(getString(R.string.dbname_users))
                .orderByChild(getString(R.string.field_user_id))
                .equalTo(mFriends.get(i));
        query.addListenerForSingleValueEvent(new ValueEventListener() {
            @Override
            public void onDataChange(DataSnapshot dataSnapshot) {
                for(DataSnapshot singleSnapshot : dataSnapshot.getChildren()){

                    mUserList.add(singleSnapshot.getValue(User.class));
                }
                if(count >= mFriends.size() - 1){
                    updateUsersList();
                }
            }

            @Override
            public void onCancelled(DatabaseError databaseError) {

            }
        });
    }
}


private void getFriends(){
    Log.d(TAG, "getFollowing: searching for FRIENDS **************************************");
    mFriends.clear();
    mUserList.clear();
    DatabaseReference reference = FirebaseDatabase.getInstance().getReference();
    Query query = reference
            .child(getString(R.string.dbname_friends))
            .child(FirebaseAuth.getInstance().getCurrentUser().getUid());
    query.addListenerForSingleValueEvent(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
            for (DataSnapshot singleSnapshot : dataSnapshot.getChildren()) {
                Log.d(TAG, "onDataChange: found friend----------------**: " + singleSnapshot.getValue(User.class).toString());

                mFriends.add(singleSnapshot.child(getString(R.string.field_user_id)).getValue().toString());

                Log.d(TAG, "onDataChange: Freinds user id: " + mFriends.toString() );
            }

            updateFriendsList();
        }

        @Override
        public void onCancelled(DatabaseError databaseError) {

        }
    });
}

- TheRapidSloth

Answer 1

看一下这个：

 DatabaseReference dref;  
   ListView listview;  
   ArrayList<String> list=new ArrayList<>();  
   @Override  
   protected void onCreate(Bundle savedInstanceState) {  
     super.onCreate(savedInstanceState);  
     setContentView(R.layout.activity_main);  
     listview=(ListView)findViewById(R.id.listview);  
     final ArrayAdapter<String> adapter=new ArrayAdapter<String>(this,android.R.layout.simple_dropdown_item_1line,list);  
     listview.setAdapter(adapter);  
     dref=FirebaseDatabase.getInstance().getReference();  
     dref.addChildEventListener(new ChildEventListener() {  
       @Override  
       public void onChildAdded(DataSnapshot dataSnapshot, String s) {  
         list.add(dataSnapshot.getValue(String.class));  
         adapter.notifyDataSetChanged();  
       }  
       @Override  
       public void onChildChanged(DataSnapshot dataSnapshot, String s) {  
       }  
       @Override  
       public void onChildRemoved(DataSnapshot dataSnapshot) {  
         list.remove(dataSnapshot.getValue(String.class));  
         adapter.notifyDataSetChanged();  
       }  
       @Override  
       public void onChildMoved(DataSnapshot dataSnapshot, String s) {  
       }  
       @Override  
       public void onCancelled(DatabaseError databaseError) {  
       }  
     });  
   }  

- Vansh Badkul

---

啊，现在我明白了。谢谢。 - TheRapidSloth

Answer 2

无论何时您在friendList上收到firebase更新，都可以在适配器上调用adapter.notifyDataSetChanged()，这样适配器就会知道需要执行更新。

我建议您使用RecyclerView，因为它比listview更灵活。

- MezzDroid

---

我并不完全理解这个答案。据我所知，在getFriendsList()中从Firebase接收数据（onDataChange），然后在其中放置adapter.notifyDataSetChanged()（我不知道是否应该放在那里）。如果您可以，请详细说明，以便我能够理解。 - TheRapidSloth

好的，让我简单解释一下。每当您想更新列表时，请调用notifydatasetchanged()。例如，如果您在Firebase中添加了一个新朋友，请使用新值更新mUserList，并在adapter上调用adapter.notifydatasetchanged()。 - MezzDroid