add structure

lib/pages/po/po_files.dart

@@ -0,0 +1,27 @@
+import 'dart:io';
+
+class POFiles {
+  File poPaymentFile, storageChargeFile;
+  List<File> poPaymentFilesAdded=[];
+  List<String> poPaymentFilesRemoved=[]; // only url
+  bool poFileChanged = false, storageFileChanged = false;
+
+  set addPoPaymentFile(File file) {
+    poPaymentFilesAdded.add(file);
+    poFileChanged = true;
+  }
+
+  set removePoPaymentFile(String url) {
+    poPaymentFilesRemoved.add(url);
+    poFileChanged = true;
+  }
+
+  set setStorageChargeFile(File file) {
+    storageChargeFile = file;
+    storageFileChanged = true;
+  }
+
+  bool get anyChanged => poFileChanged || storageFileChanged;
+
+
+}