java Android Firebase数据库子节点

Question

我有一个Firebase数据库结构，如下所示：

the firebase database structure

现在我想访问节点“comingSoonPages”中的项到一个模型类。如何获取对该节点中这些不同用户指定项的引用

数据库参考：

mUpcomingDatabaseReference = mFirebaseDatabase.getReference().child("comingSoonPages").child("blrKoramangala")

现在，引用的侦听器如下所示：

mValueEventListener = new ValueEventListener() {
    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {
        for (DataSnapshot snapShot : dataSnapshot.getChildren()){
            Log.e("snap" , String.valueOf(snapShot));
            try{
                UpcomingProperty property = snapShot.getValue(UpcomingProperty.class);
                Log.e("name" , String.valueOf(property.getName()));
            }catch (Exception ex){
                ex.printStackTrace();
            }
        }
    }

    @Override
    public void onCancelled(DatabaseError databaseError) {

    }
};
mUpcomingDatabaseReference.addValueEventListener(mValueEventListener);

当我尝试记录每个节点中的名称时，我得到了NPE，值为null

我正在映射的模型类是：

public class UpcomingProperty implements Serializable {

    //private Amenities amenities;
    private List<String> amenities;
    private Coordinates coordinates;
    private Image image;
    private String link;
    private String location;
    private String name;
    private Text text;
    private List<String> sortParameter;
    private EarlyBird earlyBird;

    public UpcomingProperty(){}

    public List<String> getAmenities() {
        return amenities;
    }

    public void setAmenities(List<String> amenities) {
        this.amenities = amenities;
    }

    public Coordinates getCoordinates() {
        return coordinates;
    }

    public void setCoordinates(Coordinates coordinates) {
        this.coordinates = coordinates;
    }

    public Image getImage() {
        return image;
    }

    public void setImage(Image image) {
        this.image = image;
    }

    public String getLink() {
        return link;
    }

    public void setLink(String link) {
        this.link = link;
    }

    public String getLocation() {
        return location;
    }

    public void setLocation(String location) {
        this.location = location;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public Text getText() {
        return text;
    }

    public void setText(Text text) {
        this.text = text;
    }

    public List<String> getSortParameter() {
        return sortParameter;
    }

    public void setSortParameter(List<String> sortParameter) {
        this.sortParameter = sortParameter;
    }

    public EarlyBird getEarlyBird() {
        return earlyBird;
    }

    public void setEarlyBird(EarlyBird earlyBird) {
        this.earlyBird = earlyBird;
    }
}

谢谢

扩展firebase节点： extended node values

Answer 1

要获取该数据，请使用以下代码：

DatabaseReference rootRef = FirebaseDatabase.getInstance().getReference();
DatabaseReference comingSoonPagesRef = rootRef.child("comingSoonPages");
ValueEventListener eventListener = new ValueEventListener() {
    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {
        for(DataSnapshot ds : dataSnapshot.getChildren()) {
            String name = ds.child("name").getValue(String.class);
            Log.d("TAG", name);
        }
    }

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

唯一的名字将是out。但是你也可以用同样的方法得到所有其他的值

如果要使用model类，请使用以下代码：

DatabaseReference rootRef = FirebaseDatabase.getInstance().getReference();
DatabaseReference comingSoonPagesRef = rootRef.child("comingSoonPages");
ValueEventListener eventListener = new ValueEventListener() {
    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {
        for(DataSnapshot ds : dataSnapshot.getChildren()) {
            UpcomingProperty upcomingProperty = ds.getValue(UpcomingProperty.class);
            Log.d("TAG", upcomingProperty.getName());
        }
    }

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

您将获得相同的输出

Answer 2

假设comingSoonPages包含一个项列表，如果希望访问该项的所有子节点，则需要在comingSoonPages引用上添加一个^{}

DatabaseReference upcomingItemsRef = mFirebaseDatabase.getReference().child("comingSoonPages");

ChildEventListener childEventListener = new ChildEventListener() {
     @Override
     public void onChildAdded(DataSnapshot dataSnapshot, String previousChildName) {
         if(dataSnapshot.exists()) {
             // Handle each individual node like blrKoramangala, cyberHub here.
             String key = dataSnapshot.getKey();
             // Get the UpcomingProperty object here.
             UpcomingProperty property = dataSnapshot.getValue(UpcomingProperty.class);
             Log.d(TAG, "property.getName():" + property.getName();
         }
     }
     // Other methods of ChildEventListener go here
};
upcomingItemsRef.addChildEventListener(childEventListener);

您可以阅读有关使用数据列表here的更多信息

然而，如果这不是一个清单，下面是你做错了什么：

@Override
public void onDataChange(DataSnapshot dataSnapshot) {
    // Don't do this. It will get the children of blrKoramangala and
    // those won't be of UpcomingProperty type. 
    // Remove and replace with dataSnapshot.exists()
    for (DataSnapshot snapShot : dataSnapshot.getChildren()){
    ...
    }
}