我从firebase数据库中检索到的文本没有出现在我的列表视图中

Posted 2021-04-01

这是我的数据库的屏幕截图：

这是活动：

private ListView dishList;
private Button bAddNewDish;
private DishListAdapter dishListAdapter;
private FirebaseDatabase mFireDb;
private DatabaseReference mDbReference;
private ChildEventListener mChildListener;

@Override
protected void onCreate(@Nullable Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.dishes);

    dishList = (ListView) findViewById(R.id.dishList);
    bAddNewDish = (Button) findViewById(R.id.bAddNewDish);

    mFireDb = FirebaseDatabase.getInstance();
    mDbReference = mFireDb.getReference().child("dishlist");
    ArrayList<DishElement> dishArray = new ArrayList<>();
    dishListAdapter = new DishListAdapter(this,R.layout.dish_item_element,dishArray);
    dishList.setAdapter(dishListAdapter);

    mChildListener = new ChildEventListener() {
        @Override
        public void onChildAdded(DataSnapshot dataSnapshot, String s) {

            DishElement dishElement = dataSnapshot.getValue(DishElement.class);
            dishListAdapter.add(dishElement);

        }

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

            DishElement dishElement = dataSnapshot.getValue(DishElement.class);
            dishListAdapter.add(dishElement);

        }

        @Override
        public void onChildRemoved(DataSnapshot dataSnapshot) {

            DishElement dishElement = dataSnapshot.getValue(DishElement.class);
            dishListAdapter.add(dishElement);

        }

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

        }

        @Override
        public void onCancelled(DatabaseError databaseError) {

        }
    };

    mDbReference.addChildEventListener(mChildListener);

    bAddNewDish.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            Intent i = new Intent(view.getContext(),AddDish.class);
            startActivity(i);
        }
    });
}

}

这是适配器：

public class DishListAdapter extends ArrayAdapter<DishElement> {

public DishListAdapter(@NonNull Context context, int resource, ArrayList<DishElement> dishElements) {
    super(context, resource, dishElements);
}

@NonNull
@Override
public View getView(int position, @Nullable View convertView, @NonNull ViewGroup parent) {

    DishElement dishElement = getItem(position);

    if(convertView == null){
        convertView = LayoutInflater.from((Activity) getContext()).inflate(R.layout.dish_item_element,parent,false);
    }

    TextView dishName = (TextView) convertView.findViewById(R.id.dishName);
    dishName.setText(dishElement.getName());

    return convertView;
}

}

我用dishElement.getName()方法得到null作为值。数据库连接似乎工作正常，但每当在我的数据库中添加子节点时，我都没有获得此字符串值。

答案

您在读取数据时遇到问题，因为您的字段未正确命名。要解决此问题，请使用如下所示的模型类：

public class DishElement {
    private String description, image, menuId, name;
    private double price;

    public DishElement() {}

    public DishElement(String description, String image, String menuId, String name, double price) {
        this.description = description;
        this.image = image;
        this.menuId = menuId;
        this.name = name;
        this.price = price;
    }

    public String getDescription() {return description;}

    public String getImage() {return image;}

    public String getMenuId() {return menuId;}

    public String getName() {return name;}

    public double getPrice() {return price;}
}

要实际正确读取数据，请从数据库中删除旧数据并添加新数据。

要读取数据，请使用以下代码：

DatabaseReference rootRef = FirebaseDatabase.getInstance().getReference();
DatabaseReference dishListRef = rootRef.child("dishlist");
ValueEventListener eventListener = new ValueEventListener() {
    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {
        for(DataSnapshot ds : dataSnapshot.getChildren()) {
            DishElement dishElement = ds.getValue(DishElement.class);
            dishListAdapter.add(dishElement);
            Log.d("TAG", dishElement.getName());
        }
    }

    @Override
    public void onCancelled(DatabaseError databaseError) {}
};
dishListRef.addListenerForSingleValueEvent(eventListener);

如您所见，我添加了一个日志语句来打印出名称：

dishElement.getName()

在这种情况下肯定会起作用。在你的情况下没有工作，因为Firebase正在寻找一个名为name而不是Name（大写N）的字段。