Menghitung jumlah semua (sum) nilai dari child "total", kotlin firebase

https://drive.google.com/open?id=1kKralGYGdZuimkrxxIGaRMH8OI6-D_gJ https://drive.google.com/open?id=1IJ9RQIxOkuw17rKU5TJp7SlyPJRjK_-p

idperiod?.onItemSelectedListener = object : AdapterView.OnItemSelectedListener {
            override fun onItemSelected(p0: AdapterView<*>?, p1: View?, p2: Int, p3: Long) {
                val periode = idperiod.selectedItem.toString()
                idsearch.setOnClickListener {
                    val mdatabase = FirebaseDatabase.getInstance().getReference("Transaction").orderByChild("periode")
                        .startAt(periode).endAt(periode + "\uf8ff")
                    mdatabase.addValueEventListener(object : ValueEventListener {
                        override fun onCancelled(p0: DatabaseError) {
                            TODO("not implemented") //To change body of created functions use File | Settings | File Templates.
                        }

                        override fun onDataChange(p0: DataSnapshot) {
                            var sum = 0
                            p0.children.forEach {
                                val total = it.getValue(transaction::class.java)?.total
                                val pValue = total?.toInt()
                                sum += pValue!!

                            }
                            idTotal.text = sum.toString()

                        }

                    })
                }
            }