alexeyinkin commented on code in PR #24457:
URL: https://github.com/apache/beam/pull/24457#discussion_r1067719822


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playground/frontend/playground_components/lib/src/controllers/public_notifier.dart:
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@@ -0,0 +1,23 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import 'package:flutter/material.dart';
+
+class PublicNotifier extends ChangeNotifier {

Review Comment:
   We aim to eliminate the use of `Provider`s because they make it hard to 
refactor, and Flutter team even [refuses to think about this 
problem](https://github.com/flutter/flutter/issues/116768).
   
   As for 'get_it', you can think of it as just as a global map of objects with 
compile-time type safety of entries. It implements the 'service locator' 
pattern, this is why we populate it in `locator.dart`.
   
   This class on its own is just a notifier that can be triggered from outside 
and passes its change signal to whoever listens to it. It is only compensating 
for the standard `ChangeNotifier`'s inability to be triggered from outside and 
has nothing to do with `get_it`.
   
   It then has multiple use cases. One of them is to pass both an event emitter 
and its trigger into a function:
   
   
https://github.com/akvelon/beam/blob/dc4e142f25e1c7efa23b26a04158e1f208ea3864/learning/tour-of-beam/frontend/lib/components/login/button.dart#L32
   
   This is a null-safe improvement over the previous solution:
   
   
https://github.com/apache/beam/blob/e21b5b79a25dec5555389a87c3d638219d09e2c9/learning/tour-of-beam/frontend/lib/components/login/login_button.dart#L39
   
   The new solution is also reusable while before we had to copy the entire 
method code for each overlay.



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