我无法从 Firebase 数据库中获取数据

Question

我将 Firebase 用于 Android 项目，它在将数据推送到服务器时运行良好，但在检索数据时，我什么也得不到。

这是我的火力基地的结构

这是我从 Firebase 中检索数据的代码

mRef.child("User").addValueEventListener(new ValueEventListener() {
         @Override
         public void onDataChange(DataSnapshot dataSnapshot) {

             counter = dataSnapshot.getChildrenCount();
             for (DataSnapshot postSnapshot : dataSnapshot.getChildren()) {
                 post = postSnapshot.getValue(SettersGetters.class);
                 nicuNames.add(post.getNicuName());
                 nicuAddresses.add(post.getNicuAddress());
                 niucCount.add(post.getNicuCount());
                 nicuPrices.add(post.getNicuCount());
                 nicuPhones.add(post.getNicuPhone());
                 nicuUpdate.add(post.getNicuUpdate());
                 nicuLat.add(post.getNicuLat());
                 nicuLng.add(post.getNicuLng());
                 nicuDes.add(post.getNicuDesc());
                 a++;
                 Toast.makeText(MapsActivity.this,"jhkjhk", Toast.LENGTH_LONG).show();
                 System.out.println(nicuNames.get(0));
             }
             //Toast.makeText(MapsActivity.this,"jhkjhk" + a, Toast.LENGTH_LONG).show();
         }

         @Override
         public void onCancelled(DatabaseError databaseError) {

         }

     });

在制作 Toast 以至少打印 Children 的数量时，它每次都返回 0

Toast.makeText(MapsActivity.this,a+"",Toast.LENGTH_SHORT).show();

Answer 1

您想监听 User 键的子事件，而不是值事件。

替换

mRef.child("User").addValueEventListener(new ValueEventListener() {

与

mRef.child("User").addChildEventListener(new ChildEventListener() {

---

然后，实施

• onChildAdded(DataSnapshot snapshot, String previousChildName)

• onChildChanged(DataSnapshot snapshot, String previousChildName)

从那里，您将 DataSnapshot 映射到（最好比命名更好的类）SettersGetters.class

Answer 2

试试这个

mRef.child("User").child("Kfx7408plvgugiMR1Se").addValueEventListener(new ValueEventListener(){
         @Override
         public void onDataChange(DataSnapshot dataSnapshot) {

             counter = dataSnapshot.getChildrenCount();
             for (DataSnapshot postSnapshot : dataSnapshot.getChildren()) {
                 post = postSnapshot.getValue(SettersGetters.class);
                 nicuNames.add(post.getNicuName());
                 nicuAddresses.add(post.getNicuAddress());
                 niucCount.add(post.getNicuCount());
                 nicuPrices.add(post.getNicuCount());
                 nicuPhones.add(post.getNicuPhone());
                 nicuUpdate.add(post.getNicuUpdate());
                 nicuLat.add(post.getNicuLat());
                 nicuLng.add(post.getNicuLng());
                 nicuDes.add(post.getNicuDesc());
                 a++;
                 Toast.makeText(MapsActivity.this,"jhkjhk", Toast.LENGTH_LONG).show();
                 System.out.println(nicuNames.get(0));
             }
             //Toast.makeText(MapsActivity.this,"jhkjhk" + a, Toast.LENGTH_LONG).show();
         }

         @Override
         public void onCancelled(DatabaseError databaseError) {

         }

     });