当onChildAdded事件被触发时，如何在Firebase中获取父项？

Question

考虑下面的代码示例：

// Get a reference to our posts
Firebase ref = new Firebase("https://docs-examples.firebaseio.com/web/saving-data/fireblog/posts");
ref.addChildEventListener(new ChildEventListener() {
// Retrieve new posts as they are added to the database
@Override
public void onChildAdded(DataSnapshot snapshot, String previousChildKey) {
    BlogPost newPost = snapshot.getValue(BlogPost.class);
    System.out.println("Author: " + newPost.getAuthor());
    System.out.println("Title: " + newPost.getTitle());
}
//... ChildEventListener also defines onChildChanged, onChildRemoved,
//    onChildMoved and onCanceled, covered in later sections.
});

当onChildAdded被触发时，是否可以在Firebase中获取DataSnapshot父项目？

Answer 1

由于您只检索了子项，因此DataSnapshot不包含父项的数据。但在ref上可以很容易地访问它。

public void onChildAdded(DataSnapshot snapshot, String previousChildKey) {
  ref.addListenerForSingleValueEvent(new ValueEventListener() {
    public void onDataChange(DataSnapshot parent) {
      System.out.println("Got parent");
    }
    ...
  });
}

Answer 2

我知道这个帖子已经很老了，但下面是对我有用的

@Override
public void onChildChanged(@NonNull DataSnapshot dataSnapshot, @Nullable String s) {
       DatabaseReference parent = dataSnapshot.getRef().getParent();
       if( parent != null){
             String parentNode = parent.getKey();
       }
 }

因此，基本上在Datasnapshot上调用.getRef()、.getParent()、.getKey()就可以了。