在不知道值键的情况下读取孩子的值

Question

我想获取之前推送的特定数据值（绿色圈出）。但是当我运行这段代码时，它也会显示密钥。

This is the Structure

我推送数据的类：

FirebaseUser user = FirebaseAuth.getInstance().getCurrentUser();
String uid = user.getEmail();
DatabaseReference reference = FirebaseDatabase.getInstance().getReference("Users");

reference.child(user.getUid()).child("Distance").push().setValue(LastValueRounded);
reference.child(user.getUid()).child("Speed").push().setValue(averagespeed);
reference.child(user.getUid()).child("Time").push().setValue(getTimerText());

我应该读取数据的类：

mAuth = FirebaseAuth.getInstance();
FirebaseUser user = mAuth.getCurrentUser();
String uid = user.getEmail();
DatabaseReference reference = 
    FirebaseDatabase.getInstance()
                    .getReference("Users");

reference.orderByChild("email")
         .equalTo(uid)
         .addValueEventListener(
    new ValueEventListener() {
        @Override
        public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
            for (DataSnapshot snapshot : dataSnapshot.getChildren()) {
                if (snapshot.child("Distance").getValue() != null) {
                    String distance1 = snapshot.child("Distance").getValue().toString();
                    String speed1 = snapshot.child("Speed").getValue().toString();
                    String time1 = snapshot.child("Time").getValue().toString();
                 
                    distance.setText(distance1);
                    speed.setText(speed1);
                    time.setText(time1);
                }
            }
        }        

        @Override
        public void onCancelled(@NonNull DatabaseError databaseError) {
            Log.w("ERROR", "onCancelled", databaseError.toException());
        }
    });

The displayed data

Answer 1

我怀疑您的“getValue()”返回一个 Map 对象。你可以试试：

String distance1 = (String)(snapshot.child("Distance").getValue().get("MJw...9") );

Answer 2

当您使用以下参考时：

DatabaseReference reference = FirebaseDatabase.getInstance().getReference("Users");
reference.orderByChild("email")
     .equalTo(uid)
     .addValueEventListener(/* ... /*);

这意味着您正在尝试获取“用户”节点下的所有子节点，其中“电子邮件”字段包含经过身份验证的用户的 UID 的值，但这不正确，因为在“用户”节点下有没有这样的孩子。为了能够仅获取与那些推送的元素对应的值，请使用以下代码行：

String uid = FirebaseAuth.getInstance().getCurrentUser().getUid();
DatabaseReference rootRef = FirebaseDatabase.getInstance().getReference();
DatabaseReference uidRef = rootRef.child("Users").child(uid);
uidRef.get().addOnCompleteListener(new OnCompleteListener<DataSnapshot>() {
    @Override
    public void onComplete(@NonNull Task<DataSnapshot> task) {
        if (task.isSuccessful()) {
            DataSnapshot snapshot = task.getResult();
            for (DataSnapshot distanceSnapshot : snapshot.child("Distance").getChildren()) {
                distance.setText(distanceSnapshot.getValue(String.class));
            }
            for (DataSnapshot speedSnapshot : snapshot.child("Speed").getChildren()) {
                speed.setText(speedSnapshot.getValue(String.class));
            }
            for (DataSnapshot timeSnapshot : snapshot.child("Time").getChildren()) {
                time.setText(timeSnapshot.getValue(String.class));
            }
        } else {
            Log.d("TAG", task.getException().getMessage()); //Don't ignore potential errors!
        }
    }
});