如何从Firebase检索多个数据项并将这些字符串合并在一起？

Question

I have a Firebase database which stores data for student timetables. The locations of the multiple items of data are as follows:

Module = Timetable > Course > Day > Time > MODULE_DATA

Room = Timetable > Course > Day > Time > ROOM_DATA

My aim is to retrieve these items of data into two Strings and merge them together into a single String. However the problem I came across that retrieving items of data require separate onDataChange methods which means I cannot access the string outside of this in order to merge it with another.

This is my code to retrieve the Module data:

                //Monday
    for (i = 9; i <= 18; i++) {
        String time = Integer.toString(i);
        final String MonTime = "Mon" + i;

        DatabaseReference Module = mRef.child("Monday").child(time).child("Module");
        Monday.addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(DataSnapshot dataSnapshot) {
                String MonValue = dataSnapshot.getValue(String.class);
                int id = getResources().getIdentifier(MonTime, "id", getPackageName());
                TextView Monday = (TextView) findViewById(id);
                Monday.setText(MonValue);
            }

            @Override
            public void onCancelled(DatabaseError databaseError) {

            }
        });
    }

Effectively I want to do the same thing for the following Database reference and merge the string values together:

            DatabaseReference Room= mRef.child("Monday").child(time).child("Room");

Answer 1

Assuming you structured your database the way I think you did, this should work. I'm confused as to why you said you couldn't do this in one ValueEventListener. I also took out that loop.

mRef.child("Monday").orderByKey().startAt("9").endAt("18").addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
            for(DataSnapshot child : dataSnapshot.getChildren()) {
                HashMap<String, String> value = (HashMap<String, String>) child.getValue();
                String module = value.get("module");
                String room = value.get("room");
                System.out.println(room + module);
            }
        }

        @Override
        public void onCancelled(DatabaseError databaseError) {

        }
    });

Edit

With loop:

for (i = 9; i <= 18; i++) {
        String time = Integer.toString(i);
        final String MonTime = "Mon" + i;

        dbRef.child("Monday").child(time).addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(DataSnapshot dataSnapshot) {
                String module = dataSnapshot.child("Module").getValue(String.class);
                String room = dataSnapshot.child("Room").getValue(String.class);
                int id = getResources().getIdentifier(MonTime, "id", getPackageName());
                TextView Monday = (TextView) findViewById(id);
                Monday.setText(MonValue);
            }

            @Override
            public void onCancelled(DatabaseError databaseError) {

            }
        });
}

Answer 2

I found the way to return the data using snapshot foreach

 firebase.database().ref('events').once('value',(data)=>{
      //console.log(data.toJSON());
      data.forEach(function(snapshot){
        var newPost = snapshot.val();
        console.log("description: " + newPost.description);
        console.log("interest: " + newPost.interest);
        console.log("players: " + newPost.players);
        console.log("uid: " + newPost.uid);
        console.log("when: " + newPost.when);
        console.log("where: " + newPost.where);
      })

      })