packages/flutter/lib/src/cupertino/page_scaffold.dart - external/github.com/flutter/flutter - Git at Google

 // Copyright 2014 The Flutter Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.

 import 'package:flutter/widgets.dart';

 import 'colors.dart';
 import 'theme.dart';

 /// Implements a single iOS application page's layout.
 ///
 /// The scaffold lays out the navigation bar on top and the content between or
 /// behind the navigation bar.
 ///
 /// When tapping a status bar at the top of the CupertinoPageScaffold, an
 /// animation will complete for the current primary [ScrollView], scrolling to
 /// the beginning. This is done using the [PrimaryScrollController] that
 /// encloses the [ScrollView]. The [ScrollView.primary] flag is used to connect
 /// a [ScrollView] to the enclosing [PrimaryScrollController].
 ///
 /// {@tool dartpad}
 /// This example shows a [CupertinoPageScaffold] with a [ListView] as a [child].
 /// The [CupertinoButton] is connected to a callback that increments a counter.
 /// The [backgroundColor] can be changed.
 ///
 /// ** See code in examples/api/lib/cupertino/page_scaffold/cupertino_page_scaffold.0.dart **
 /// {@end-tool}
 ///
 /// See also:
 ///
 ///  * [CupertinoTabScaffold], a similar widget for tabbed applications.
 ///  * [CupertinoPageRoute], a modal page route that typically hosts a
 ///    [CupertinoPageScaffold] with support for iOS-style page transitions.
 class CupertinoPageScaffold extends StatefulWidget {
   /// Creates a layout for pages with a navigation bar at the top.
   const CupertinoPageScaffold({
     Key? key,
     this.navigationBar,
     this.backgroundColor,
     this.resizeToAvoidBottomInset = true,
     required this.child,
   }) : assert(child != null),
        assert(resizeToAvoidBottomInset != null),
        super(key: key);

   /// The [navigationBar], typically a [CupertinoNavigationBar], is drawn at the
   /// top of the screen.
   ///
   /// If translucent, the main content may slide behind it.
   /// Otherwise, the main content's top margin will be offset by its height.
   ///
   /// The scaffold assumes the navigation bar will account for the [MediaQuery]
   /// top padding, also consume it if the navigation bar is opaque.
   ///
   /// By default `navigationBar` has its text scale factor set to 1.0 and does
   /// not respond to text scale factor changes from the operating system, to match
   /// the native iOS behavior. To override such behavior, wrap each of the `navigationBar`'s
   /// components inside a [MediaQuery] with the desired [MediaQueryData.textScaleFactor]
   /// value. The text scale factor value from the operating system can be retrieved
   /// in many ways, such as querying [MediaQuery.textScaleFactorOf] against
   /// [CupertinoApp]'s [BuildContext].
   // TODO(xster): document its page transition animation when ready
   final ObstructingPreferredSizeWidget? navigationBar;

   /// Widget to show in the main content area.
   ///
   /// Content can slide under the [navigationBar] when they're translucent.
   /// In that case, the child's [BuildContext]'s [MediaQuery] will have a
   /// top padding indicating the area of obstructing overlap from the
   /// [navigationBar].
   final Widget child;

   /// The color of the widget that underlies the entire scaffold.
   ///
   /// By default uses [CupertinoTheme]'s `scaffoldBackgroundColor` when null.
   final Color? backgroundColor;

   /// Whether the [child] should size itself to avoid the window's bottom inset.
   ///
   /// For example, if there is an onscreen keyboard displayed above the
   /// scaffold, the body can be resized to avoid overlapping the keyboard, which
   /// prevents widgets inside the body from being obscured by the keyboard.
   ///
   /// Defaults to true and cannot be null.
   final bool resizeToAvoidBottomInset;

   @override
   State<CupertinoPageScaffold> createState() => _CupertinoPageScaffoldState();
 }

 class _CupertinoPageScaffoldState extends State<CupertinoPageScaffold> {

   void _handleStatusBarTap() {
     final ScrollController? _primaryScrollController = PrimaryScrollController.of(context);
     // Only act on the scroll controller if it has any attached scroll positions.
     if (_primaryScrollController != null && _primaryScrollController.hasClients) {
       _primaryScrollController.animateTo(
         0.0,
         // Eyeballed from iOS.
         duration: const Duration(milliseconds: 500),
         curve: Curves.linearToEaseOut,
       );
     }
   }

   @override
   Widget build(BuildContext context) {
     Widget paddedContent = widget.child;

     final MediaQueryData existingMediaQuery = MediaQuery.of(context);
     if (widget.navigationBar != null) {
       // TODO(xster): Use real size after partial layout instead of preferred size.
       // https://github.com/flutter/flutter/issues/12912
       final double topPadding =
           widget.navigationBar!.preferredSize.height + existingMediaQuery.padding.top;

       // Propagate bottom padding and include viewInsets if appropriate
       final double bottomPadding = widget.resizeToAvoidBottomInset
           ? existingMediaQuery.viewInsets.bottom
           : 0.0;

       final EdgeInsets newViewInsets = widget.resizeToAvoidBottomInset
           // The insets are consumed by the scaffolds and no longer exposed to
           // the descendant subtree.
           ? existingMediaQuery.viewInsets.copyWith(bottom: 0.0)
           : existingMediaQuery.viewInsets;

       final bool fullObstruction = widget.navigationBar!.shouldFullyObstruct(context);

       // If navigation bar is opaquely obstructing, directly shift the main content
       // down. If translucent, let main content draw behind navigation bar but hint the
       // obstructed area.
       if (fullObstruction) {
         paddedContent = MediaQuery(
           data: existingMediaQuery
           // If the navigation bar is opaque, the top media query padding is fully consumed by the navigation bar.
           .removePadding(removeTop: true)
           .copyWith(
             viewInsets: newViewInsets,
           ),
           child: Padding(
             padding: EdgeInsets.only(top: topPadding, bottom: bottomPadding),
             child: paddedContent,
           ),
         );
       } else {
         paddedContent = MediaQuery(
           data: existingMediaQuery.copyWith(
             padding: existingMediaQuery.padding.copyWith(
               top: topPadding,
             ),
             viewInsets: newViewInsets,
           ),
           child: Padding(
             padding: EdgeInsets.only(bottom: bottomPadding),
             child: paddedContent,
           ),
         );
       }
     } else {
       // If there is no navigation bar, still may need to add padding in order
       // to support resizeToAvoidBottomInset.
       final double bottomPadding = widget.resizeToAvoidBottomInset
           ? existingMediaQuery.viewInsets.bottom
           : 0.0;
       paddedContent = Padding(
         padding: EdgeInsets.only(bottom: bottomPadding),
         child: paddedContent,
       );
     }

     return DecoratedBox(
       decoration: BoxDecoration(
         color: CupertinoDynamicColor.maybeResolve(widget.backgroundColor, context)
             ?? CupertinoTheme.of(context).scaffoldBackgroundColor,
       ),
       child: Stack(
         children: <Widget>[
           // The main content being at the bottom is added to the stack first.
           paddedContent,
           if (widget.navigationBar != null)
             Positioned(
               top: 0.0,
               left: 0.0,
               right: 0.0,
               child: MediaQuery(
                 data: existingMediaQuery.copyWith(textScaleFactor: 1),
                 child: widget.navigationBar!,
               ),
             ),
           // Add a touch handler the size of the status bar on top of all contents
           // to handle scroll to top by status bar taps.
           Positioned(
             top: 0.0,
             left: 0.0,
             right: 0.0,
             height: existingMediaQuery.padding.top,
             child: GestureDetector(
               excludeFromSemantics: true,
               onTap: _handleStatusBarTap,
             ),
           ),
         ],
       ),
     );
   }
 }

 /// Widget that has a preferred size and reports whether it fully obstructs
 /// widgets behind it.
 ///
 /// Used by [CupertinoPageScaffold] to either shift away fully obstructed content
 /// or provide a padding guide to partially obstructed content.
 abstract class ObstructingPreferredSizeWidget implements PreferredSizeWidget {
   /// If true, this widget fully obstructs widgets behind it by the specified
   /// size.
   ///
   /// If false, this widget partially obstructs.
   bool shouldFullyObstruct(BuildContext context);
 }
	// Copyright 2014 The Flutter Authors. All rights reserved.
	// Use of this source code is governed by a BSD-style license that can be
	// found in the LICENSE file.

	import 'package:flutter/widgets.dart';

	import 'colors.dart';
	import 'theme.dart';

	/// Implements a single iOS application page's layout.
	///
	/// The scaffold lays out the navigation bar on top and the content between or
	/// behind the navigation bar.
	///
	/// When tapping a status bar at the top of the CupertinoPageScaffold, an
	/// animation will complete for the current primary [ScrollView], scrolling to
	/// the beginning. This is done using the [PrimaryScrollController] that
	/// encloses the [ScrollView]. The [ScrollView.primary] flag is used to connect
	/// a [ScrollView] to the enclosing [PrimaryScrollController].
	///
	/// {@tool dartpad}
	/// This example shows a [CupertinoPageScaffold] with a [ListView] as a [child].
	/// The [CupertinoButton] is connected to a callback that increments a counter.
	/// The [backgroundColor] can be changed.
	///
	/// See code in examples/api/lib/cupertino/page_scaffold/cupertino_page_scaffold.0.dart
	/// {@end-tool}
	///
	/// See also:
	///
	/// * [CupertinoTabScaffold], a similar widget for tabbed applications.
	/// * [CupertinoPageRoute], a modal page route that typically hosts a
	/// [CupertinoPageScaffold] with support for iOS-style page transitions.
	class CupertinoPageScaffold extends StatefulWidget {
	/// Creates a layout for pages with a navigation bar at the top.
	const CupertinoPageScaffold({
	Key? key,
	this.navigationBar,
	this.backgroundColor,
	this.resizeToAvoidBottomInset = true,
	required this.child,
	}) : assert(child != null),
	assert(resizeToAvoidBottomInset != null),
	super(key: key);

	/// The [navigationBar], typically a [CupertinoNavigationBar], is drawn at the
	/// top of the screen.
	///
	/// If translucent, the main content may slide behind it.
	/// Otherwise, the main content's top margin will be offset by its height.
	///
	/// The scaffold assumes the navigation bar will account for the [MediaQuery]
	/// top padding, also consume it if the navigation bar is opaque.
	///
	/// By default `navigationBar` has its text scale factor set to 1.0 and does
	/// not respond to text scale factor changes from the operating system, to match
	/// the native iOS behavior. To override such behavior, wrap each of the `navigationBar`'s
	/// components inside a [MediaQuery] with the desired [MediaQueryData.textScaleFactor]
	/// value. The text scale factor value from the operating system can be retrieved
	/// in many ways, such as querying [MediaQuery.textScaleFactorOf] against
	/// [CupertinoApp]'s [BuildContext].
	// TODO(xster): document its page transition animation when ready
	final ObstructingPreferredSizeWidget? navigationBar;

	/// Widget to show in the main content area.
	///
	/// Content can slide under the [navigationBar] when they're translucent.
	/// In that case, the child's [BuildContext]'s [MediaQuery] will have a
	/// top padding indicating the area of obstructing overlap from the
	/// [navigationBar].
	final Widget child;

	/// The color of the widget that underlies the entire scaffold.
	///
	/// By default uses [CupertinoTheme]'s `scaffoldBackgroundColor` when null.
	final Color? backgroundColor;

	/// Whether the [child] should size itself to avoid the window's bottom inset.
	///
	/// For example, if there is an onscreen keyboard displayed above the
	/// scaffold, the body can be resized to avoid overlapping the keyboard, which
	/// prevents widgets inside the body from being obscured by the keyboard.
	///
	/// Defaults to true and cannot be null.
	final bool resizeToAvoidBottomInset;

	@override
	State<CupertinoPageScaffold> createState() => _CupertinoPageScaffoldState();
	}

	class _CupertinoPageScaffoldState extends State<CupertinoPageScaffold> {

	void _handleStatusBarTap() {
	final ScrollController? _primaryScrollController = PrimaryScrollController.of(context);
	// Only act on the scroll controller if it has any attached scroll positions.
	if (_primaryScrollController != null && _primaryScrollController.hasClients) {
	_primaryScrollController.animateTo(
	0.0,
	// Eyeballed from iOS.
	duration: const Duration(milliseconds: 500),
	curve: Curves.linearToEaseOut,
	);
	}
	}

	@override
	Widget build(BuildContext context) {
	Widget paddedContent = widget.child;

	final MediaQueryData existingMediaQuery = MediaQuery.of(context);
	if (widget.navigationBar != null) {
	// TODO(xster): Use real size after partial layout instead of preferred size.
	// https://github.com/flutter/flutter/issues/12912
	final double topPadding =
	widget.navigationBar!.preferredSize.height + existingMediaQuery.padding.top;

	// Propagate bottom padding and include viewInsets if appropriate
	final double bottomPadding = widget.resizeToAvoidBottomInset
	? existingMediaQuery.viewInsets.bottom
	: 0.0;

	final EdgeInsets newViewInsets = widget.resizeToAvoidBottomInset
	// The insets are consumed by the scaffolds and no longer exposed to
	// the descendant subtree.
	? existingMediaQuery.viewInsets.copyWith(bottom: 0.0)
	: existingMediaQuery.viewInsets;

	final bool fullObstruction = widget.navigationBar!.shouldFullyObstruct(context);

	// If navigation bar is opaquely obstructing, directly shift the main content
	// down. If translucent, let main content draw behind navigation bar but hint the
	// obstructed area.
	if (fullObstruction) {
	paddedContent = MediaQuery(
	data: existingMediaQuery
	// If the navigation bar is opaque, the top media query padding is fully consumed by the navigation bar.
	.removePadding(removeTop: true)
	.copyWith(
	viewInsets: newViewInsets,
	),
	child: Padding(
	padding: EdgeInsets.only(top: topPadding, bottom: bottomPadding),
	child: paddedContent,
	),
	);
	} else {
	paddedContent = MediaQuery(
	data: existingMediaQuery.copyWith(
	padding: existingMediaQuery.padding.copyWith(
	top: topPadding,
	),
	viewInsets: newViewInsets,
	),
	child: Padding(
	padding: EdgeInsets.only(bottom: bottomPadding),
	child: paddedContent,
	),
	);
	}
	} else {
	// If there is no navigation bar, still may need to add padding in order
	// to support resizeToAvoidBottomInset.
	final double bottomPadding = widget.resizeToAvoidBottomInset
	? existingMediaQuery.viewInsets.bottom
	: 0.0;
	paddedContent = Padding(
	padding: EdgeInsets.only(bottom: bottomPadding),
	child: paddedContent,
	);
	}

	return DecoratedBox(
	decoration: BoxDecoration(
	color: CupertinoDynamicColor.maybeResolve(widget.backgroundColor, context)
	?? CupertinoTheme.of(context).scaffoldBackgroundColor,
	),
	child: Stack(
	children: <Widget>[
	// The main content being at the bottom is added to the stack first.
	paddedContent,
	if (widget.navigationBar != null)
	Positioned(
	top: 0.0,
	left: 0.0,
	right: 0.0,
	child: MediaQuery(
	data: existingMediaQuery.copyWith(textScaleFactor: 1),
	child: widget.navigationBar!,
	),
	),
	// Add a touch handler the size of the status bar on top of all contents
	// to handle scroll to top by status bar taps.
	Positioned(
	top: 0.0,
	left: 0.0,
	right: 0.0,
	height: existingMediaQuery.padding.top,
	child: GestureDetector(
	excludeFromSemantics: true,
	onTap: _handleStatusBarTap,
	),
	),
	],
	),
	);
	}
	}

	/// Widget that has a preferred size and reports whether it fully obstructs
	/// widgets behind it.
	///
	/// Used by [CupertinoPageScaffold] to either shift away fully obstructed content
	/// or provide a padding guide to partially obstructed content.
	abstract class ObstructingPreferredSizeWidget implements PreferredSizeWidget {
	/// If true, this widget fully obstructs widgets behind it by the specified
	/// size.
	///
	/// If false, this widget partially obstructs.
	bool shouldFullyObstruct(BuildContext context);
	}