Update state management.

lib/foundation/global_state.dart

@@ -0,0 +1,66 @@
+import 'package:flutter/widgets.dart';
+
+abstract class GlobalState {
+  static final _state = <Pair<Object?, State>>[];
+
+  static void register(State state, [Object? key]) {
+    _state.add(Pair(key, state));
+  }
+
+  static T find<T extends State>([Object? key]) {
+    for (var pair in _state) {
+      if (pair.left == key && pair.right is T) {
+        return pair.right as T;
+      }
+    }
+    throw Exception('State not found');
+  }
+
+  static T? findOrNull<T extends State>([Object? key]) {
+    for (var pair in _state) {
+      if (pair.left == key && pair.right is T) {
+        return pair.right as T;
+      }
+    }
+    return null;
+  }
+
+  static void unregister(State state, [Object? key]) {
+    _state.removeWhere(
+        (pair) => (key == null || pair.left == key) && pair.right == state);
+  }
+}
+
+class Pair<K, V> {
+  K left;
+  V right;
+
+  Pair(this.left, this.right);
+}
+
+abstract class AutomaticGlobalState<T extends StatefulWidget>
+    extends State<T> {
+  @override
+  @mustCallSuper
+  void initState() {
+    super.initState();
+    GlobalState.register(this, key);
+  }
+
+  @override
+  @mustCallSuper
+  void dispose() {
+    super.dispose();
+    GlobalState.unregister(this, key);
+  }
+
+  Object? get key;
+
+  void update() {
+    setState(() {});
+  }
+
+  void refresh() {
+    update();
+  }
+}