add prompt confirmation and update carton

lib/pages/receiving/receiving_editor.dart

@@ -150,9 +150,13 @@ class _ReceivingEditorState extends State<ReceivingEditor> {
               icon:
                   new Icon(CupertinoIcons.back, color: primaryColor, size: 30),
               onPressed: () {
-                showConfirmDialog(context, "back.button_confirm", () {
+                if (isDataChanged()) {
+                  showConfirmDialog(context, "back.button_confirm", () {
+                    Navigator.of(context).pop();
+                  });
+                } else {
                   Navigator.of(context).pop();
-                });
+                }
               },
             ),
             shadowColor: Colors.transparent,
@@ -253,4 +257,22 @@ class _ReceivingEditorState extends State<ReceivingEditor> {
       });
     }
   }
+
+  isDataChanged() {
+    if (_isNew) {
+      return _trackingIDCtl.text != "" ||
+          _remarkCtl.text != "" ||
+          user != null ||
+          _multiImgController.getAddedFile.isNotEmpty;
+    } else {
+      var _package = Package(
+          trackingID: _trackingIDCtl.text,
+          remark: _remarkCtl.text,
+          fcsID: user.fcsID,
+          photoUrls: widget.package.photoUrls);
+      return widget.package.isChangedForEdit(_package) ||
+          _multiImgController.getAddedFile.isNotEmpty ||
+          _multiImgController.getDeletedUrl.isNotEmpty;
+    }
+  }
 }