add structure

lib/vo/announcement.dart

@@ -0,0 +1,38 @@
+import 'package:cloud_firestore/cloud_firestore.dart';
+
+class Announcement {
+  String id;
+  String name;
+  String text;
+  DateTime time;
+
+  Announcement({this.id, this.name, this.text, this.time});
+
+  bool fromToday() {
+    var now = DateTime.now();
+    if (time == null) return false;
+    return time.day == now.day &&
+        time.month == now.month &&
+        time.year == now.year;
+  }
+
+  factory Announcement.fromMap(Map<String, dynamic> map, String id) {
+    var _time = (map['time'] as Timestamp);
+
+    return Announcement(
+      id: id,
+      time: _time?.toDate(),
+      name: map['name'],
+      text: map['text'],
+    );
+  }
+
+  Map<String, dynamic> toMap() {
+    return {'id': id, 'name': name, 'text': text};
+  }
+
+  @override
+  String toString() {
+    return 'Announcement{id:$id,name:$name,text:$text}';
+  }
+}