[CP-stable] Support CupertinoSliverNavigationBar.search with condensed large title (#162912)

Original PR: flutter/flutter#159120

The next stable branch has `CupertinoSliverNavigationBar.search`, but it is currently [unusable](flutter/flutter#159120 (comment)). The linked PR adds the search functionality and makes it usable.

Author: victorsanni

examples/api/lib/cupertino/nav_bar/cupertino_sliver_nav_bar.1.dart

@@ -4,7 +4,7 @@
 
 import 'package:flutter/cupertino.dart';
 
-/// Flutter code sample for [CupertinoSliverNavigationBar].
+/// Flutter code sample for [CupertinoSliverNavigationBar.search].
 
 void main() => runApp(const SliverNavBarApp());
 
@@ -76,18 +76,27 @@ class SliverNavBarExample extends StatelessWidget {
   }
 }
 
-class NextPage extends StatelessWidget {
+class NextPage extends StatefulWidget {
   const NextPage({super.key, this.bottomMode = NavigationBarBottomMode.automatic});
 
   final NavigationBarBottomMode bottomMode;
 
+  @override
+  State<NextPage> createState() => _NextPageState();
+}
+
+class _NextPageState extends State<NextPage> {
+  bool searchIsActive = false;
+  late String text;
+
   @override
   Widget build(BuildContext context) {
     final Brightness brightness = CupertinoTheme.brightnessOf(context);
     return CupertinoPageScaffold(
       child: CustomScrollView(
         slivers: <Widget>[
           CupertinoSliverNavigationBar.search(
+            stretch: true,
             backgroundColor: CupertinoColors.systemYellow,
             border: Border(
               bottom: BorderSide(
@@ -97,16 +106,47 @@ class NextPage extends StatelessWidget {
             ),
             middle: const Text('Contacts Group'),
             largeTitle: const Text('Family'),
-            bottomMode: bottomMode,
-          ),
-          const SliverFillRemaining(
-            child: Column(
-              mainAxisAlignment: MainAxisAlignment.spaceEvenly,
-              children: <Widget>[
-                Text('Drag me up', textAlign: TextAlign.center),
-                Text('Tap on the leading button to navigate back', textAlign: TextAlign.center),
-              ],
+            bottomMode: widget.bottomMode,
+            searchField: CupertinoSearchTextField(
+              autofocus: searchIsActive,
+              placeholder: searchIsActive ? 'Enter search text' : 'Search',
+              onChanged: (String value) {
+                setState(() {
+                  if (value.isEmpty) {
+                    text = 'Type in the search field to show text here';
+                  } else {
+                    text = 'The text has changed to: $value';
+                  }
+                });
+              },
             ),
+            onSearchableBottomTap: (bool value) {
+              text = 'Type in the search field to show text here';
+              setState(() {
+                searchIsActive = value;
+              });
+            },
+          ),
+          SliverFillRemaining(
+            child:
+                searchIsActive
+                    ? ColoredBox(
+                      color: CupertinoColors.extraLightBackgroundGray,
+                      child: Center(child: Text(text, textAlign: TextAlign.center)),
+                    )
+                    : const Padding(
+                      padding: EdgeInsets.symmetric(horizontal: 16.0),
+                      child: Column(
+                        mainAxisAlignment: MainAxisAlignment.spaceEvenly,
+                        children: <Widget>[
+                          Text('Drag me up', textAlign: TextAlign.center),
+                          Text(
+                            'Tap on the search field to open the search view',
+                            textAlign: TextAlign.center,
+                          ),
+                        ],
+                      ),
+                    ),
           ),
         ],
       ),

examples/api/test/cupertino/nav_bar/cupertino_sliver_nav_bar.1_test.dart

@@ -91,6 +91,43 @@ void main() {
     expect(tester.getBottomLeft(find.byType(CupertinoSearchTextField)).dy, 87.0);
   });
 
+  testWidgets('Opens the search view when the search field is tapped', (WidgetTester tester) async {
+    await tester.pumpWidget(const example.SliverNavBarApp());
+
+    // Navigate to a page with a search field.
+    final Finder nextButton = find.text('Bottom Automatic mode');
+    expect(nextButton, findsOneWidget);
+    await tester.tap(nextButton);
+    await tester.pumpAndSettle();
+
+    expect(find.widgetWithText(CupertinoSearchTextField, 'Search'), findsOneWidget);
+    expect(find.text('Tap on the search field to open the search view'), findsOneWidget);
+    // A decoy 'Cancel' button used in the animation.
+    expect(find.widgetWithText(CupertinoButton, 'Cancel'), findsOneWidget);
+
+    // Tap on the search field to open the search view.
+    await tester.tap(find.byType(CupertinoSearchTextField), warnIfMissed: false);
+    await tester.pumpAndSettle();
+
+    expect(find.widgetWithText(CupertinoSearchTextField, 'Enter search text'), findsOneWidget);
+    expect(find.text('Tap on the search field to open the search view'), findsNothing);
+    expect(find.widgetWithText(CupertinoButton, 'Cancel'), findsOneWidget);
+
+    await tester.enterText(find.byType(CupertinoSearchTextField), 'a');
+    await tester.pumpAndSettle();
+
+    expect(find.text('The text has changed to: a'), findsOneWidget);
+
+    // Tap on the 'Cancel' button to close the search view.
+    await tester.tap(find.widgetWithText(CupertinoButton, 'Cancel'));
+    await tester.pumpAndSettle();
+
+    expect(find.widgetWithText(CupertinoSearchTextField, 'Search'), findsOneWidget);
+    expect(find.text('Tap on the search field to open the search view'), findsOneWidget);
+    // A decoy 'Cancel' button used in the animation.
+    expect(find.widgetWithText(CupertinoButton, 'Cancel'), findsOneWidget);
+  });
+
   testWidgets('CupertinoSliverNavigationBar with previous route has back button', (
     WidgetTester tester,
   ) async {
@@ -104,7 +141,7 @@ void main() {
     expect(nextButton1, findsNothing);
 
     // Go back to the previous page.
-    final Finder backButton1 = find.byType(CupertinoButton);
+    final Finder backButton1 = find.byType(CupertinoButton).first;
     expect(backButton1, findsOneWidget);
     await tester.tap(backButton1);
     await tester.pumpAndSettle();
@@ -118,7 +155,7 @@ void main() {
     expect(nextButton2, findsNothing);
 
     // Go back to the previous page.
-    final Finder backButton2 = find.byType(CupertinoButton);
+    final Finder backButton2 = find.byType(CupertinoButton).first;
     expect(backButton2, findsOneWidget);
     await tester.tap(backButton2);
     await tester.pumpAndSettle();