add package

lib/vo/package.dart

@@ -12,13 +12,14 @@ class Package {
 
   int rate;
   int weight;
-  int amount;
   String packageType;
   String pickUpID;
   List<String> photos;
   String remark;
   DateTime arrivedDate;
 
+  int get amount => rate != null && weight != null ? rate * weight : 0;
+
   String get packageNumber =>
       shipmentNumber + "-" + receiverNumber + " #" + boxNumber;
   double get price => rate.toDouble() * weight;
@@ -35,7 +36,6 @@ class Package {
       this.boxNumber,
       this.rate,
       this.weight,
-      this.amount,
       this.packageType,
       this.pickUpID,
       this.remark,