從Firebase中刪除notifyDataSetChanged（）;不刷新ListView

Question

基本上從Firebase刪除對象後，notifyDataSetChanged()不會實時更新它。我試圖從適配器本身刪除對象，但它也失敗。

回到這個片段顯示更新列表，但我認爲這是因爲添加了小孩。這是我的代碼。

public class ArchiveFragment extends Fragment { 

    public static ArchiveFragment newInstance(Beer beer) { 
     ArchiveFragment archiveFragment = new ArchiveFragment(); 
     if (beer != null) { 
      Bundle args = new Bundle(); 
      args.putSerializable("beer", beer); 
      archiveFragment.setArguments(args); 
     } 
     return archiveFragment; 
    } 

    public ArchiveFragment(){} 

    private ArrayList<Beer> beerDB = new ArrayList<>(); 
    private ListView beerList; 
    private RecyclerView beerRec; 
    private DatabaseReference mDatabase; 

    @Override 
    public View onCreateView(LayoutInflater inflater, ViewGroup container, 
          Bundle savedInstanceState) { 
     final View view = inflater.inflate(R.layout.archive_fragment, container, false); 
     final Activity activity = getActivity(); 
     FirebaseUser user = FirebaseAuth.getInstance().getCurrentUser(); 
     beerList = (ListView)view.findViewById(R.id.beerList); 
     final ArrayAdapter<Beer> arrayAdapter = new ArrayAdapter<Beer>(getActivity(), android.R.layout.simple_list_item_1,beerDB); 
     mDatabase = FirebaseDatabase.getInstance().getReference().child("Users").child(user.getUid()).child("BeerList"); 
     beerList.setAdapter(arrayAdapter); 

     beerList.setOnItemClickListener(new AdapterView.OnItemClickListener() { 
      @Override 
      public void onItemClick(AdapterView<?> adapterView, View view, int i, long l) { 
       Object deletedBeer = beerList.getItemAtPosition(i); 
       Beer delBeer = (Beer) deletedBeer; 
       deleteBeer(delBeer.getKey()); 
      } 
     }); 

     mDatabase.addChildEventListener(new ChildEventListener() { 
      @Override 
      public void onChildAdded(DataSnapshot dataSnapshot, String s) { 
       Beer value = dataSnapshot.getValue(Beer.class); 
       value.setKey(dataSnapshot.getKey()); 
       beerDB.add(value); 

       arrayAdapter.notifyDataSetChanged(); 
      } 

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

      @Override 
      public void onChildRemoved(DataSnapshot dataSnapshot) { 

       String key = dataSnapshot.getKey(); 
       beerDB.remove(key); 
       arrayAdapter.notifyDataSetChanged(); 
      } 

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

      @Override 
      public void onCancelled(DatabaseError databaseError) {} 
     }); 

     return view; 
    } 

    public void deleteBeer(String key){ 
     mDatabase.child(key).removeValue(); 
    } 
} 

Answer 1

你從你的ArrayList使用remove功能這是不正確刪除的項目。 remove函數獲取ArrayList中需要刪除的項目索引。但在這裏，當您從dataSnapshot獲得密鑰時，它與您的ArrayList的任何索引都不匹配，因此該項目實際上並未從您的ArrayList中刪除。所以你需要改變你的onChildRemoved這樣的功能。

@Override 
public void onChildRemoved(DataSnapshot dataSnapshot) { 

    String key = dataSnapshot.getKey(); 

    for (int i = 0; i < beerDB.size(); i++) { 
     // Find the item to remove and then remove it by index 
     if (beerDB.get(i).key.equals(key)) { 
      beerDB.remove(i); 
      break; 
     } 
    } 

    arrayAdapter.notifyDataSetChanged(); 
}