(squash) move onChannelSelect default up to public widget

Author: gnprice

lib/widgets/subscription_list.dart

@@ -31,6 +31,10 @@ class SubscriptionListPageBody extends StatefulWidget {
   //     https://github.com/zulip/zulip-flutter/pull/1774#discussion_r2249032503
   final bool disableChannelActionSheet;
   final bool hideChannelsIfUserCantPost;
+
+  /// Callback to invoke when the user selects a channel from the list.
+  ///
+  /// If null, the default behavior is to navigate to the channel feed.
   final OnChannelSelectCallback? onChannelSelect;
   // TODO(#412) add onTopicSelect
 
@@ -82,6 +86,12 @@ class _SubscriptionListPageBodyState extends State<SubscriptionListPageBody> wit
     });
   }
 
+  void _handleChannelSelect(ChannelNarrow narrow) {
+    Navigator.push(context,
+      MessageListPage.buildRoute(context: context,
+        narrow: narrow));
+  }
+
   @override
   Widget build(BuildContext context) {
     // Design referenced from:
@@ -124,6 +134,7 @@ class _SubscriptionListPageBodyState extends State<SubscriptionListPageBody> wit
         message: zulipLocalizations.channelsEmptyPlaceholder);
     }
 
+    final onChannelSelect = widget.onChannelSelect ?? _handleChannelSelect;
     return SafeArea(
       // Don't pad the bottom here; we want the list content to do that.
       //
@@ -144,15 +155,15 @@ class _SubscriptionListPageBodyState extends State<SubscriptionListPageBody> wit
               unreadsModel: unreadsModel,
               subscriptions: pinned,
               disableChannelActionSheet: widget.disableChannelActionSheet,
-              onChannelSelect: widget.onChannelSelect),
+              onChannelSelect: onChannelSelect),
           ],
           if (unpinned.isNotEmpty) ...[
             _SubscriptionListHeader(label: zulipLocalizations.unpinnedSubscriptionsLabel),
             _SubscriptionList(
               unreadsModel: unreadsModel,
               subscriptions: unpinned,
               disableChannelActionSheet: widget.disableChannelActionSheet,
-              onChannelSelect: widget.onChannelSelect),
+              onChannelSelect: onChannelSelect),
           ],
 
           // TODO(#188): add button leading to "All Streams" page with ability to subscribe
@@ -206,13 +217,13 @@ class _SubscriptionList extends StatelessWidget {
     required this.unreadsModel,
     required this.subscriptions,
     required this.disableChannelActionSheet,
-    this.onChannelSelect,
+    required this.onChannelSelect,
   });
 
   final Unreads? unreadsModel;
   final List<Subscription> subscriptions;
   final bool disableChannelActionSheet;
-  final OnChannelSelectCallback? onChannelSelect;
+  final OnChannelSelectCallback onChannelSelect;
 
   @override
   Widget build(BuildContext context) {
@@ -227,12 +238,7 @@ class _SubscriptionList extends StatelessWidget {
           unreadCount: unreadCount,
           showMutedUnreadBadge: showMutedUnreadBadge,
           disableChannelActionSheet: disableChannelActionSheet,
-          onChannelSelect: onChannelSelect
-            ?? (narrow) {
-                Navigator.push(context,
-                  MessageListPage.buildRoute(context: context,
-                    narrow: narrow));
-              });
+          onChannelSelect: onChannelSelect);
     });
   }
 }