如何从Firebase数据库检索多个数据？

Question

这是我编写的代码，但是它返回了整个架构。

mDatabase = FirebaseDatabase.getInstance().getReference().child("/News");
    mTitle = (TextView)findViewById(R.id.title_view);

    mDatabase.addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
            String title=dataSnapshot.getValue().toString();;
            mTitle.setText(title);
        }

        @Override
        public void onCancelled(@NonNull DatabaseError databaseError) {}
    });

Answer 1

要解决此问题，只需使用以下代码行：

DatabaseReference rootRef = FirebaseDatabase.getInstance().getReference();
DatabaseReference newsRef = rootRef.child("News");
ValueEventListener valueEventListener = new ValueEventListener() {
    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {
        for(DataSnapshot ds : dataSnapshot.getChildren()) {
            String desc = ds.child("desc").getValue(String.class);
            String title = ds.child("title").getValue(String.class);
            Log.d(TAG, desc + " / " + title);
        }
    }

    @Override
    public void onCancelled(@NonNull DatabaseError databaseError) {
        Log.d(TAG, databaseError.getMessage());
    }
};
newsRef.addListenerForSingleValueEvent(valueEventListener);

您的logcat中的输出将是：

desc1 / title1
desc2 / title2

Answer 2

use this method 
//-----------------//
private void getDataFrom() {

            String userId = FirebaseAuth.getInstance().getCurrentUser().getUid();

            DatabaseReference mCustomerDatabase = FirebaseDatabase.getInstance().getReference().child("Users").child("1");

            mCustomerDatabase.addListenerForSingleValueEvent(new ValueEventListener() {
                @Override
                public void onDataChange(DataSnapshot dataSnapshot) {
                    if (dataSnapshot.exists() && dataSnapshot.getChildrenCount() > 0) {
                        Map<String, Object> map = (Map<String, Object>) dataSnapshot.getValue();
                        if (map.get("title") != null) {
                            customer_name = map.get("title").toString();
                            Log.i("customer_name",String.valueOf(customer_name));

                        }

                    }
                }

                @Override
                public void onCancelled(DatabaseError databaseError) {
                }
            });
        }

Answer 3

这就是我获取所有Firebase数据的方式

     DatabaseReference databaseReference = FirebaseDatabase.getInstance().getReference();
    DatabaseReference db = databaseReference.child("Customers");
            arrayList = new ArrayList<>();
            db.addValueEventListener(new ValueEventListener() {
                @Override
                public void onDataChange(DataSnapshot dataSnapshot) {

                    for(DataSnapshot snapshot : dataSnapshot.getChildren())
                    {

                          arrayList.add(snapshot.getValue(Customer_Details2.class));
                    }



                    checkUpdate();
                }

                @Override
                public void onCancelled(DatabaseError databaseError) {

                }
            });