Added viewport fraction parameter to tabView (#98512)

packages/flutter/lib/src/material/tabs.dart

@@ -1328,6 +1328,7 @@ class TabBarView extends StatefulWidget {
     this.controller,
     this.physics,
     this.dragStartBehavior = DragStartBehavior.start,
+    this.viewportFraction = 1.0,
   }) : assert(children != null),
        assert(dragStartBehavior != null),
        super(key: key);
@@ -1358,6 +1359,9 @@ class TabBarView extends StatefulWidget {
   /// {@macro flutter.widgets.scrollable.dragStartBehavior}
   final DragStartBehavior dragStartBehavior;
 
+  /// {@macro flutter.widgets.pageview.viewportFraction}
+  final double viewportFraction;
+
   @override
   State<TabBarView> createState() => _TabBarViewState();
 }
@@ -1411,7 +1415,10 @@ class _TabBarViewState extends State<TabBarView> {
     super.didChangeDependencies();
     _updateTabController();
     _currentIndex = _controller!.index;
-    _pageController = PageController(initialPage: _currentIndex!);
+    _pageController = PageController(
+      initialPage: _currentIndex!,
+      viewportFraction: widget.viewportFraction,
+    );
   }
 
   @override

packages/flutter/lib/src/widgets/page_view.dart

@@ -144,10 +144,12 @@ class PageController extends ScrollController {
   ///    locations used to save scroll offsets.
   final bool keepPage;
 
+  /// {@template flutter.widgets.pageview.viewportFraction}
   /// The fraction of the viewport that each page should occupy.
   ///
   /// Defaults to 1.0, which means each page fills the viewport in the scrolling
   /// direction.
+  /// {@endtemplate}
   final double viewportFraction;
 
   /// The current page displayed in the controlled [PageView].

packages/flutter/test/material/tabs_test.dart

@@ -1017,6 +1017,93 @@ void main() {
     expect(position.pixels, 800);
   });
 
+  testWidgets('TabBarView viewportFraction sets PageView viewport fraction', (WidgetTester tester) async {
+    const Duration animationDuration = Duration(milliseconds: 100);
+    final List<String> tabs = <String>['A', 'B', 'C'];
+
+    final TabController tabController = TabController(
+      vsync: const TestVSync(),
+      initialIndex: 1,
+      length: tabs.length,
+      animationDuration: animationDuration,
+    );
+    await tester.pumpWidget(boilerplate(
+      child: Column(
+        children: <Widget>[
+          TabBar(
+            tabs: tabs.map<Widget>((String tab) => Tab(text: tab)).toList(),
+            controller: tabController,
+          ),
+          SizedBox(
+            width: 400.0,
+            height: 400.0,
+            child: TabBarView(
+              viewportFraction: 0.8,
+              controller: tabController,
+              children: const <Widget>[
+                Center(child: Text('0')),
+                Center(child: Text('1')),
+                Center(child: Text('2')),
+              ],
+            ),
+          ),
+        ],
+      ),
+    ));
+
+    expect(tabController.index, 1);
+
+    final PageView pageView = tester.widget(find.byType(PageView));
+    final PageController pageController = pageView.controller;
+
+    // The TabView was initialized with viewportFraction as 0.8
+    // So it's expected the PageView inside would obtain the same viewportFraction
+    expect(pageController.viewportFraction, 0.8);
+  });
+
+  testWidgets('TabBarView viewportFraction is 1 by default', (WidgetTester tester) async {
+    const Duration animationDuration = Duration(milliseconds: 100);
+    final List<String> tabs = <String>['A', 'B', 'C'];
+
+    final TabController tabController = TabController(
+      vsync: const TestVSync(),
+      initialIndex: 1,
+      length: tabs.length,
+      animationDuration: animationDuration,
+    );
+    await tester.pumpWidget(boilerplate(
+      child: Column(
+        children: <Widget>[
+          TabBar(
+            tabs: tabs.map<Widget>((String tab) => Tab(text: tab)).toList(),
+            controller: tabController,
+          ),
+          SizedBox(
+            width: 400.0,
+            height: 400.0,
+            child: TabBarView(
+              controller: tabController,
+              children: const <Widget>[
+                Center(child: Text('0')),
+                Center(child: Text('1')),
+                Center(child: Text('2')),
+              ],
+            ),
+          ),
+        ],
+      ),
+    ));
+
+    expect(tabController.index, 1);
+
+    final PageView pageView = tester.widget(find.byType(PageView));
+    final PageController pageController = pageView.controller;
+
+    // The TabView was initialized with default viewportFraction
+    // So it's expected the PageView inside would obtain the value 1
+    expect(pageController.viewportFraction, 1);
+  });
+
   testWidgets('TabBar tap skips indicator animation when disabled in controller', (WidgetTester tester) async {
     final List<String> tabs = <String>['A', 'B'];