Activity TextView不显示Firebase中的内容，而Push通知仅在活动内部有效？

Question

I'm having a big or little problem, I want to show the specific message por each of my orders put it takes one and print it for the three of them and the push notification appears when I open the activity here is my code from java and xml

public class MessageActivity extends AppCompatActivity {

    public TextView message;
    private DatabaseReference mDatabase;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_message);

        mDatabase = FirebaseDatabase.getInstance().getReference().child("users").child("paid").child(FirebaseAuth.getInstance().getCurrentUser().getUid());

        message = findViewById(R.id.message);
        mDatabase.addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(DataSnapshot dataSnapshot) {
                for (DataSnapshot areaSnapshot : dataSnapshot.getChildren()) {
                    DetailCart detail = areaSnapshot.getValue(DetailCart.class);
                    String mess = detail.getMessage();
                    message.setText(mess);
                    NotificationManager notif=(NotificationManager)getSystemService(Context.NOTIFICATION_SERVICE);
                    Notification notify=new Notification.Builder
                            (getApplicationContext()).setContentTitle(mess).setContentText(mess).
                            setContentTitle(mess).setSmallIcon(R.drawable.ic_person).build();
                    notify.flags |= Notification.FLAG_AUTO_CANCEL;
                    notif.notify(0, notify);
                }
            }

            @Override
            public void onCancelled(DatabaseError databaseError) {    
                // [START_EXCLUDE]
                System.out.println("The read failed: " + databaseError.getMessage());
            }
        });
    }
}

This is the layout code:

<TextView
    android:id="@+id/message"
    android:textSize="20dp"
    android:layout_marginBottom="5dp"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:text="Message"
    android:textColor="@android:color/holo_blue_dark"
    android:textColorHighlight="@android:color/primary_text_dark" />

Answer 1

I add this to my code and it worked It's only missing the push notification outside the activity

if (detail.getUidrequest().equals(item.getUidrequest())){

                    String mess = detail.getMessage();
                    message.setText(mess);
                    NotificationManager notif=(NotificationManager)getSystemService(Context.NOTIFICATION_SERVICE);
                    Notification notify=new Notification.Builder
                            (getApplicationContext()).setContentTitle(mess).setContentText(mess).
                            setContentTitle(mess).setSmallIcon(R.drawable.ic_person).build();
                    notify.flags |= Notification.FLAG_AUTO_CANCEL;
                    notif.notify(0, notify);

                }