add setting, alertbox, etc

ui/lib/utils.dart

@@ -0,0 +1,31 @@
+import 'package:flutter/material.dart';
+
+class Utils {
+  static Future<void> showAlertDialog(BuildContext context, String msg) async {
+
+    return showDialog<void>(
+      context: context,
+      barrierDismissible: true, // user must tap button!
+      builder: (BuildContext context) {
+        return AlertDialog(
+          title: const Text('警告 ⚠️'),
+          content: SingleChildScrollView(
+            child: ListBody(
+              children: <Widget>[
+                Text(msg),
+              ],
+            ),
+          ),
+          actions: <Widget>[
+            TextButton(
+              child: const Text('确定'),
+              onPressed: () {
+                Navigator.of(context).pop();
+              },
+            ),
+          ],
+        );
+      },
+    );
+  }
+}