Android Firebase：检索ArrayList中的所有数据，并从该ArrayList中随机选择字符串

Question

我正在使用Firebase创建一个应用，用户可以在其中分享报价。数据插入成功，在插入每个值后，它在数据库中看起来像这样。 请查看此图像以获取数据库值：

我想获取ArrayList中的所有数据。并且public View onCreateView(LayoutInflater paramLayoutInflater, ViewGroup paramViewGroup, Bundle paramBundle) { this.localView = paramLayoutInflater.inflate(R.layout.fragmenthome, paramViewGroup, false); story = (TextView) localView.findViewById(R.id.story_text); rl = (RelativeLayout) localView.findViewById(R.id.rlLayout); linearLayout = (LinearLayout) localView.findViewById(R.id.bottom_bar); imgRefresh = (ImageView) localView.findViewById(R.id.refreshStory); databaseReference = FirebaseDatabase.getInstance().getReference().child("stories"); databaseReference.addValueEventListener(new ValueEventListener() { @Override public void onDataChange(DataSnapshot dataSnapshot) { storiesary = new ArrayList<String>(); for (DataSnapshot childSnapshot: dataSnapshot.getChildren()) { storiesary.add(childSnapshot.getValue().toString()); } } @Override public void onCancelled(DatabaseError databaseError) { } }); imgRefresh.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View v) { setStory(); } }); return localView; } public void setStory() { int arraysize = storiesary.size(); final int arrayposition1 = (new Random()).nextInt(arraysize); story.setText(storiesary.get(arrayposition1)); } 的刷新按钮应该将TextView更新为将从ArrayList中随机选择的新值。我尝试过这样的事情。但它不起作用。它显示nullpointerexception。

{{1}}

Answer 1

试试这个

databaseReference.addValueEventListener(new ValueEventListener() {
     @Override
     public void onDataChange(DataSnapshot dataSnapshot) {
         storiesary = new ArrayList<String>();
         for (DataSnapshot childSnapshot: dataSnapshot.getChildren()) {
               HashMap map =(HashMap) childSnapshot.getValue();
               if(map!=null) {
                   storiesary.add(map.get("storytext"));
               }
               //or 
              String name = (String) childSnapshot.child("storytext").getValue();
          }
      }

      @Override
      public void onCancelled(DatabaseError databaseError) {
         Log.d(TAG,"Error");
      }
   });