add two decimal and add confirm dialog if press back button

lib/pages/carton/carton_cargo_table.dart

@@ -1,5 +1,6 @@
 import 'package:fcs/domain/entities/cargo_type.dart';
 import 'package:fcs/helpers/theme.dart';
+import 'package:fcs/pages/main/util.dart';
 import 'package:fcs/pages/widgets/local_text.dart';
 import 'package:fcs/pages/widgets/my_data_table.dart';
 import 'package:flutter/cupertino.dart';
@@ -25,6 +26,8 @@ class CargoTable extends StatefulWidget {
 
 class _CargoTableState extends State<CargoTable> {
   double totalWeight = 0;
+  List<CargoType> _cargos = [];
+  double remainingWeight = 0;
   @override
   Widget build(BuildContext context) {
     return MyDataTable(
@@ -54,12 +57,13 @@ class _CargoTableState extends State<CargoTable> {
       return [];
     }
 
-    double _total = 0;
     var rows = widget.cargoTypes.map((c) {
-      _total += c.weight;
-
       return MyDataRow(
         onSelectChanged: (bool selected) async {
+          if (this.totalWeight <= 0) {
+            showMsgDialog(context, "Error", "Please insert total weight");
+            return;
+          }
           CargoType cargo = await Navigator.push<CargoType>(
               context,
               CupertinoPageRoute(
@@ -67,6 +71,12 @@ class _CargoTableState extends State<CargoTable> {
                         cargo: c,
                       )));
           if (widget.onAdd != null) widget.onAdd(cargo);
+          if (cargo == null) return;
+
+          this._cargos.add(cargo);
+          if (this.remainingWeight <= 0) return;
+          this.remainingWeight -= cargo.weight;
+          print("this.remainingWeight>>>${this.remainingWeight}");
         },
         cells: [
           MyDataCell(new Text(
@@ -104,6 +114,7 @@ class _CargoTableState extends State<CargoTable> {
         if (_t == null) return;
         setState(() {
           totalWeight = _t;
+          remainingWeight = _t;
         });
       },
       cells: [