action_sheet: Add and use PageRoot

Author: chrisbobbe

lib/widgets/action_sheet.dart

@@ -24,6 +24,7 @@ import 'emoji_reaction.dart';
 import 'icons.dart';
 import 'inset_shadow.dart';
 import 'message_list.dart';
+import 'page.dart';
 import 'store.dart';
 import 'text.dart';
 import 'theme.dart';
@@ -163,11 +164,15 @@ class ActionSheetCancelButton extends StatelessWidget {
 }
 
 /// Show a sheet of actions you can take on a topic.
+///
+/// Needs a [PageRoot] ancestor.
 void showTopicActionSheet(BuildContext context, {
   required int channelId,
   required TopicName topic,
 }) {
-  final store = PerAccountStoreWidget.of(context);
+  final pageContext = PageRoot.contextOf(context);
+
+  final store = PerAccountStoreWidget.of(pageContext);
   final subscription = store.subscriptions[channelId];
 
   final optionButtons = <ActionSheetMenuItemButton>[];
@@ -237,7 +242,7 @@ void showTopicActionSheet(BuildContext context, {
       currentVisibilityPolicy: visibilityPolicy,
       newVisibilityPolicy: to,
       narrow: TopicNarrow(channelId, topic),
-      pageContext: context);
+      pageContext: pageContext);
   }));
 
   if (optionButtons.isEmpty) {
@@ -250,7 +255,7 @@ void showTopicActionSheet(BuildContext context, {
     return;
   }
 
-  _showActionSheet(context, optionButtons: optionButtons);
+  _showActionSheet(pageContext, optionButtons: optionButtons);
 }
 
 class UserTopicUpdateButton extends ActionSheetMenuItemButton {
@@ -376,33 +381,34 @@ class UserTopicUpdateButton extends ActionSheetMenuItemButton {
 ///
 /// Must have a [MessageListPage] ancestor.
 void showMessageActionSheet({required BuildContext context, required Message message}) {
-  final store = PerAccountStoreWidget.of(context);
+  final pageContext = PageRoot.contextOf(context);
+  final store = PerAccountStoreWidget.of(pageContext);
 
   // The UI that's conditioned on this won't live-update during this appearance
   // of the action sheet (we avoid calling composeBoxControllerOf in a build
   // method; see its doc).
   // So we rely on the fact that isComposeBoxOffered for any given message list
   // will be constant through the page's life.
-  final messageListPage = MessageListPage.ancestorOf(context);
+  final messageListPage = MessageListPage.ancestorOf(pageContext);
   final isComposeBoxOffered = messageListPage.composeBoxController != null;
 
   final isMessageRead = message.flags.contains(MessageFlag.read);
   final markAsUnreadSupported = store.connection.zulipFeatureLevel! >= 155; // TODO(server-6)
   final showMarkAsUnreadButton = markAsUnreadSupported && isMessageRead;
 
   final optionButtons = [
-    ReactionButtons(message: message, pageContext: context),
-    StarButton(message: message, pageContext: context),
+    ReactionButtons(message: message, pageContext: pageContext),
+    StarButton(message: message, pageContext: pageContext),
     if (isComposeBoxOffered)
-      QuoteAndReplyButton(message: message, pageContext: context),
+      QuoteAndReplyButton(message: message, pageContext: pageContext),
     if (showMarkAsUnreadButton)
-      MarkAsUnreadButton(message: message, pageContext: context),
-    CopyMessageTextButton(message: message, pageContext: context),
-    CopyMessageLinkButton(message: message, pageContext: context),
-    ShareButton(message: message, pageContext: context),
+      MarkAsUnreadButton(message: message, pageContext: pageContext),
+    CopyMessageTextButton(message: message, pageContext: pageContext),
+    CopyMessageLinkButton(message: message, pageContext: pageContext),
+    ShareButton(message: message, pageContext: pageContext),
   ];
 
-  _showActionSheet(context, optionButtons: optionButtons);
+  _showActionSheet(pageContext, optionButtons: optionButtons);
 }
 
 abstract class MessageActionSheetMenuItemButton extends ActionSheetMenuItemButton {

lib/widgets/message_list.dart

@@ -277,7 +277,9 @@ class _MessageListPageState extends State<MessageListPage> implements MessageLis
             narrow: ChannelNarrow(streamId)))));
     }
 
-    return Scaffold(
+    // Insert a PageRoot here, to provide a context that can be used for
+    // MessageListPage.ancestorOf.
+    return PageRoot(child: Scaffold(
       appBar: ZulipAppBar(
         buildTitle: (willCenterTitle) =>
           MessageListAppBarTitle(narrow: narrow, willCenterTitle: willCenterTitle),
@@ -318,7 +320,7 @@ class _MessageListPageState extends State<MessageListPage> implements MessageLis
                 ))),
             if (ComposeBox.hasComposeBox(narrow))
               ComposeBox(key: _composeBoxKey, narrow: narrow)
-          ])));
+          ]))));
   }
 }
 

lib/widgets/page.dart

@@ -3,6 +3,30 @@ import 'package:flutter/material.dart';
 
 import 'store.dart';
 
+/// An [InheritedWidget] for near the root of a page's widget subtree,
+/// providing its [BuildContext].
+///
+/// Useful when needing a context that persists through the page's lifespan,
+/// e.g. for a show-action-sheet function
+/// whose buttons use a context to close the sheet
+/// or show an error dialog / snackbar asynchronously.
+///
+/// (In this scenario, it would be buggy to use the context of the element
+/// that was long-pressed,
+/// if the element can unmount as part of handling a Zulip event.)
+class PageRoot extends InheritedWidget {
+  const PageRoot({super.key, required super.child});
+
+  @override
+  bool updateShouldNotify(covariant PageRoot oldWidget) => false;
+
+  static BuildContext contextOf(BuildContext context) {
+    final element = context.getElementForInheritedWidgetOfExactType<PageRoot>();
+    assert(element != null, 'No PageRoot ancestor');
+    return element!;
+  }
+}
+
 /// A page route that always builds the same widget.
 ///
 /// This is useful for making the route more transparent for a test to inspect.
@@ -42,7 +66,10 @@ mixin AccountPageRouteMixin<T extends Object?> on PageRoute<T> {
       accountId: accountId,
       placeholder: loadingPlaceholderPage ?? const LoadingPlaceholderPage(),
       routeToRemoveOnLogout: this,
-      child: super.buildPage(context, animation, secondaryAnimation));
+      // PageRoot goes under PerAccountStoreWidget, so the provided context
+      // can be used for PerAccountStoreWidget.of.
+      child: PageRoot(
+        child: super.buildPage(context, animation, secondaryAnimation)));
   }
 }
 

test/widgets/test_app.dart

@@ -1,6 +1,7 @@
 import 'package:flutter/material.dart';
 
 import 'package:zulip/generated/l10n/zulip_localizations.dart';
+import 'package:zulip/widgets/page.dart';
 import 'package:zulip/widgets/store.dart';
 import 'package:zulip/widgets/theme.dart';
 
@@ -77,9 +78,9 @@ class TestZulipApp extends StatelessWidget {
         navigatorObservers: navigatorObservers ?? const [],
 
         home: accountId != null
-          ? PerAccountStoreWidget(accountId: accountId!, child: child)
-          : child,
-      );
+          ? PerAccountStoreWidget(accountId: accountId!,
+              child: PageRoot(child: child))
+          : PageRoot(child: child));
     }));
   }
 }