packages/flutter/lib/src/cupertino/picker.dart - mirrors/flutter - Git at Google

 // Copyright 2017 The Chromium 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/foundation.dart';
 import 'package:flutter/rendering.dart';
 import 'package:flutter/services.dart';
 import 'package:flutter/widgets.dart';

 /// Color of the 'magnifier' lens border.
 const Color _kHighlighterBorder = Color(0xFF7F7F7F);
 const Color _kDefaultBackground = Color(0xFFD2D4DB);
 // Eyeballed values comparing with a native picker.
 // Values closer to PI produces denser flatter lists.
 const double _kDefaultDiameterRatio = 1.35;
 const double _kDefaultPerspective = 0.004;
 /// Opacity fraction value that hides the wheel above and below the 'magnifier'
 /// lens with the same color as the background.
 const double _kForegroundScreenOpacityFraction = 0.7;

 /// An iOS-styled picker.
 ///
 /// Displays its children widgets on a wheel for selection and
 /// calls back when the currently selected item changes.
 ///
 /// Can be used with [showModalBottomSheet] to display the picker modally at the
 /// bottom of the screen.
 ///
 /// See also:
 ///
 ///  * [ListWheelScrollView], the generic widget backing this picker without
 ///    the iOS design specific chrome.
 ///  * <https://developer.apple.com/ios/human-interface-guidelines/controls/pickers/>
 class CupertinoPicker extends StatefulWidget {
   /// Creates a picker from a concrete list of children.
   ///
   /// The [diameterRatio] and [itemExtent] arguments must not be null. The
   /// [itemExtent] must be greater than zero.
   ///
   /// The [backgroundColor] defaults to light gray. It can be set to null to
   /// disable the background painting entirely; this is mildly more efficient
   /// than using [Colors.transparent].
   ///
   /// The [looping] argument decides whether the child list loops and can be
   /// scrolled infinitely.  If set to true, scrolling past the end of the list
   /// will loop the list back to the beginning.  If set to false, the list will
   /// stop scrolling when you reach the end or the beginning.
   CupertinoPicker({
     Key key,
     this.diameterRatio = _kDefaultDiameterRatio,
     this.backgroundColor = _kDefaultBackground,
     this.offAxisFraction = 0.0,
     this.useMagnifier = false,
     this.magnification = 1.0,
     this.scrollController,
     @required this.itemExtent,
     @required this.onSelectedItemChanged,
     @required List<Widget> children,
     bool looping = false,
   }) : assert(children != null),
        assert(diameterRatio != null),
        assert(diameterRatio > 0.0, RenderListWheelViewport.diameterRatioZeroMessage),
        assert(magnification > 0),
        assert(itemExtent != null),
        assert(itemExtent > 0),
        childDelegate = looping
                        ? ListWheelChildLoopingListDelegate(children: children)
                        : ListWheelChildListDelegate(children: children),
        super(key: key);

   /// Creates a picker from an [IndexedWidgetBuilder] callback where the builder
   /// is dynamically invoked during layout.
   ///
   /// A child is lazily created when it starts becoming visible in the viewport.
   /// All of the children provided by the builder are cached and reused, so
   /// normally the builder is only called once for each index (except when
   /// rebuilding - the cache is cleared).
   ///
   /// The [itemBuilder] argument must not be null. The [childCount] argument
   /// reflects the number of children that will be provided by the [itemBuilder].
   /// {@macro flutter.widgets.wheelList.childCount}
   ///
   /// The [itemExtent] argument must be non-null and positive.
   ///
   /// The [backgroundColor] defaults to light gray. It can be set to null to
   /// disable the background painting entirely; this is mildly more efficient
   /// than using [Colors.transparent].
   CupertinoPicker.builder({
     Key key,
     this.diameterRatio = _kDefaultDiameterRatio,
     this.backgroundColor = _kDefaultBackground,
     this.offAxisFraction = 0.0,
     this.useMagnifier = false,
     this.magnification = 1.0,
     this.scrollController,
     @required this.itemExtent,
     @required this.onSelectedItemChanged,
     @required IndexedWidgetBuilder itemBuilder,
     int childCount,
   }) : assert(itemBuilder != null),
        assert(diameterRatio != null),
        assert(diameterRatio > 0.0, RenderListWheelViewport.diameterRatioZeroMessage),
        assert(magnification > 0),
        assert(itemExtent != null),
        assert(itemExtent > 0),
        childDelegate = ListWheelChildBuilderDelegate(builder: itemBuilder, childCount: childCount),
        super(key: key);

   /// Relative ratio between this picker's height and the simulated cylinder's diameter.
   ///
   /// Smaller values creates more pronounced curvatures in the scrollable wheel.
   ///
   /// For more details, see [ListWheelScrollView.diameterRatio].
   ///
   /// Must not be null and defaults to `1.1` to visually mimic iOS.
   final double diameterRatio;

   /// Background color behind the children.
   ///
   /// Defaults to a gray color in the iOS color palette.
   ///
   /// This can be set to null to disable the background painting entirely; this
   /// is mildly more efficient than using [Colors.transparent].
   final Color backgroundColor;

   /// {@macro flutter.rendering.wheelList.offAxisFraction}
   final double offAxisFraction;

   /// {@macro flutter.rendering.wheelList.useMagnifier}
   final bool useMagnifier;

   /// {@macro flutter.rendering.wheelList.magnification}
   final double magnification;

   /// A [FixedExtentScrollController] to read and control the current item.
   ///
   /// If null, an implicit one will be created internally.
   final FixedExtentScrollController scrollController;

   /// The uniform height of all children.
   ///
   /// All children will be given the [BoxConstraints] to match this exact
   /// height. Must not be null and must be positive.
   final double itemExtent;

   /// An option callback when the currently centered item changes.
   ///
   /// Value changes when the item closest to the center changes.
   ///
   /// This can be called during scrolls and during ballistic flings. To get the
   /// value only when the scrolling settles, use a [NotificationListener],
   /// listen for [ScrollEndNotification] and read its [FixedExtentMetrics].
   final ValueChanged<int> onSelectedItemChanged;

   /// A delegate that lazily instantiates children.
   final ListWheelChildDelegate childDelegate;

   @override
   State<StatefulWidget> createState() => _CupertinoPickerState();
 }

 class _CupertinoPickerState extends State<CupertinoPicker> {
   int _lastHapticIndex;

   void _handleSelectedItemChanged(int index) {
     // Only the haptic engine hardware on iOS devices would produce the
     // intended effects.
     if (defaultTargetPlatform == TargetPlatform.iOS
         && index != _lastHapticIndex) {
       _lastHapticIndex = index;
       HapticFeedback.selectionClick();
     }

     if (widget.onSelectedItemChanged != null) {
       widget.onSelectedItemChanged(index);
     }
   }

   /// Makes the fade to white edge gradients.
   Widget _buildGradientScreen() {
     return Positioned.fill(
       child: IgnorePointer(
         child: Container(
           decoration: const BoxDecoration(
             gradient: LinearGradient(
               colors: <Color>[
                 Color(0xFFFFFFFF),
                 Color(0xF2FFFFFF),
                 Color(0xDDFFFFFF),
                 Color(0x00FFFFFF),
                 Color(0x00FFFFFF),
                 Color(0xDDFFFFFF),
                 Color(0xF2FFFFFF),
                 Color(0xFFFFFFFF),
               ],
               stops: <double>[
                 0.0, 0.05, 0.09, 0.22, 0.78, 0.91, 0.95, 1.0,
               ],
               begin: Alignment.topCenter,
               end: Alignment.bottomCenter,
             ),
           ),
         ),
       ),
     );
   }

   /// Makes the magnifier lens look so that the colors are normal through
   /// the lens and partially grayed out around it.
   Widget _buildMagnifierScreen() {
     final Color foreground = widget.backgroundColor?.withAlpha(
       (widget.backgroundColor.alpha * _kForegroundScreenOpacityFraction).toInt()
     );

     return IgnorePointer(
       child: Column(
         children: <Widget>[
           Expanded(
             child: Container(
               color: foreground,
             ),
           ),
           Container(
             decoration: const BoxDecoration(
               border: Border(
                 top: BorderSide(width: 0.0, color: _kHighlighterBorder),
                 bottom: BorderSide(width: 0.0, color: _kHighlighterBorder),
               )
             ),
             constraints: BoxConstraints.expand(
                 height: widget.itemExtent * widget.magnification,
             ),
           ),
           Expanded(
             child: Container(
               color: foreground,
             ),
           ),
         ],
       ),
     );
   }

   @override
   Widget build(BuildContext context) {
     Widget result = Stack(
       children: <Widget>[
         Positioned.fill(
           child: ListWheelScrollView.useDelegate(
             controller: widget.scrollController,
             physics: const FixedExtentScrollPhysics(),
             diameterRatio: widget.diameterRatio,
             perspective: _kDefaultPerspective,
             offAxisFraction: widget.offAxisFraction,
             useMagnifier: widget.useMagnifier,
             magnification: widget.magnification,
             itemExtent: widget.itemExtent,
             onSelectedItemChanged: _handleSelectedItemChanged,
             childDelegate: widget.childDelegate,
           ),
         ),
         _buildGradientScreen(),
         _buildMagnifierScreen(),
       ],
     );
     if (widget.backgroundColor != null) {
       result = DecoratedBox(
         decoration: BoxDecoration(
           color: widget.backgroundColor,
         ),
         child: result,
       );
     }
     return result;
   }
 }
	// Copyright 2017 The Chromium 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/foundation.dart';
	import 'package:flutter/rendering.dart';
	import 'package:flutter/services.dart';
	import 'package:flutter/widgets.dart';

	/// Color of the 'magnifier' lens border.
	const Color _kHighlighterBorder = Color(0xFF7F7F7F);
	const Color _kDefaultBackground = Color(0xFFD2D4DB);
	// Eyeballed values comparing with a native picker.
	// Values closer to PI produces denser flatter lists.
	const double _kDefaultDiameterRatio = 1.35;
	const double _kDefaultPerspective = 0.004;
	/// Opacity fraction value that hides the wheel above and below the 'magnifier'
	/// lens with the same color as the background.
	const double _kForegroundScreenOpacityFraction = 0.7;

	/// An iOS-styled picker.
	///
	/// Displays its children widgets on a wheel for selection and
	/// calls back when the currently selected item changes.
	///
	/// Can be used with [showModalBottomSheet] to display the picker modally at the
	/// bottom of the screen.
	///
	/// See also:
	///
	/// * [ListWheelScrollView], the generic widget backing this picker without
	/// the iOS design specific chrome.
	/// * <https://developer.apple.com/ios/human-interface-guidelines/controls/pickers/>
	class CupertinoPicker extends StatefulWidget {
	/// Creates a picker from a concrete list of children.
	///
	/// The [diameterRatio] and [itemExtent] arguments must not be null. The
	/// [itemExtent] must be greater than zero.
	///
	/// The [backgroundColor] defaults to light gray. It can be set to null to
	/// disable the background painting entirely; this is mildly more efficient
	/// than using [Colors.transparent].
	///
	/// The [looping] argument decides whether the child list loops and can be
	/// scrolled infinitely. If set to true, scrolling past the end of the list
	/// will loop the list back to the beginning. If set to false, the list will
	/// stop scrolling when you reach the end or the beginning.
	CupertinoPicker({
	Key key,
	this.diameterRatio = _kDefaultDiameterRatio,
	this.backgroundColor = _kDefaultBackground,
	this.offAxisFraction = 0.0,
	this.useMagnifier = false,
	this.magnification = 1.0,
	this.scrollController,
	@required this.itemExtent,
	@required this.onSelectedItemChanged,
	@required List<Widget> children,
	bool looping = false,
	}) : assert(children != null),
	assert(diameterRatio != null),
	assert(diameterRatio > 0.0, RenderListWheelViewport.diameterRatioZeroMessage),
	assert(magnification > 0),
	assert(itemExtent != null),
	assert(itemExtent > 0),
	childDelegate = looping
	? ListWheelChildLoopingListDelegate(children: children)
	: ListWheelChildListDelegate(children: children),
	super(key: key);

	/// Creates a picker from an [IndexedWidgetBuilder] callback where the builder
	/// is dynamically invoked during layout.
	///
	/// A child is lazily created when it starts becoming visible in the viewport.
	/// All of the children provided by the builder are cached and reused, so
	/// normally the builder is only called once for each index (except when
	/// rebuilding - the cache is cleared).
	///
	/// The [itemBuilder] argument must not be null. The [childCount] argument
	/// reflects the number of children that will be provided by the [itemBuilder].
	/// {@macro flutter.widgets.wheelList.childCount}
	///
	/// The [itemExtent] argument must be non-null and positive.
	///
	/// The [backgroundColor] defaults to light gray. It can be set to null to
	/// disable the background painting entirely; this is mildly more efficient
	/// than using [Colors.transparent].
	CupertinoPicker.builder({
	Key key,
	this.diameterRatio = _kDefaultDiameterRatio,
	this.backgroundColor = _kDefaultBackground,
	this.offAxisFraction = 0.0,
	this.useMagnifier = false,
	this.magnification = 1.0,
	this.scrollController,
	@required this.itemExtent,
	@required this.onSelectedItemChanged,
	@required IndexedWidgetBuilder itemBuilder,
	int childCount,
	}) : assert(itemBuilder != null),
	assert(diameterRatio != null),
	assert(diameterRatio > 0.0, RenderListWheelViewport.diameterRatioZeroMessage),
	assert(magnification > 0),
	assert(itemExtent != null),
	assert(itemExtent > 0),
	childDelegate = ListWheelChildBuilderDelegate(builder: itemBuilder, childCount: childCount),
	super(key: key);

	/// Relative ratio between this picker's height and the simulated cylinder's diameter.
	///
	/// Smaller values creates more pronounced curvatures in the scrollable wheel.
	///
	/// For more details, see [ListWheelScrollView.diameterRatio].
	///
	/// Must not be null and defaults to `1.1` to visually mimic iOS.
	final double diameterRatio;

	/// Background color behind the children.
	///
	/// Defaults to a gray color in the iOS color palette.
	///
	/// This can be set to null to disable the background painting entirely; this
	/// is mildly more efficient than using [Colors.transparent].
	final Color backgroundColor;

	/// {@macro flutter.rendering.wheelList.offAxisFraction}
	final double offAxisFraction;

	/// {@macro flutter.rendering.wheelList.useMagnifier}
	final bool useMagnifier;

	/// {@macro flutter.rendering.wheelList.magnification}
	final double magnification;

	/// A [FixedExtentScrollController] to read and control the current item.
	///
	/// If null, an implicit one will be created internally.
	final FixedExtentScrollController scrollController;

	/// The uniform height of all children.
	///
	/// All children will be given the [BoxConstraints] to match this exact
	/// height. Must not be null and must be positive.
	final double itemExtent;

	/// An option callback when the currently centered item changes.
	///
	/// Value changes when the item closest to the center changes.
	///
	/// This can be called during scrolls and during ballistic flings. To get the
	/// value only when the scrolling settles, use a [NotificationListener],
	/// listen for [ScrollEndNotification] and read its [FixedExtentMetrics].
	final ValueChanged<int> onSelectedItemChanged;

	/// A delegate that lazily instantiates children.
	final ListWheelChildDelegate childDelegate;

	@override
	State<StatefulWidget> createState() => _CupertinoPickerState();
	}

	class _CupertinoPickerState extends State<CupertinoPicker> {
	int _lastHapticIndex;

	void _handleSelectedItemChanged(int index) {
	// Only the haptic engine hardware on iOS devices would produce the
	// intended effects.
	if (defaultTargetPlatform == TargetPlatform.iOS
	&& index != _lastHapticIndex) {
	_lastHapticIndex = index;
	HapticFeedback.selectionClick();
	}

	if (widget.onSelectedItemChanged != null) {
	widget.onSelectedItemChanged(index);
	}
	}

	/// Makes the fade to white edge gradients.
	Widget _buildGradientScreen() {
	return Positioned.fill(
	child: IgnorePointer(
	child: Container(
	decoration: const BoxDecoration(
	gradient: LinearGradient(
	colors: <Color>[
	Color(0xFFFFFFFF),
	Color(0xF2FFFFFF),
	Color(0xDDFFFFFF),
	Color(0x00FFFFFF),
	Color(0x00FFFFFF),
	Color(0xDDFFFFFF),
	Color(0xF2FFFFFF),
	Color(0xFFFFFFFF),
	],
	stops: <double>[
	0.0, 0.05, 0.09, 0.22, 0.78, 0.91, 0.95, 1.0,
	],
	begin: Alignment.topCenter,
	end: Alignment.bottomCenter,
	),
	),
	),
	),
	);
	}

	/// Makes the magnifier lens look so that the colors are normal through
	/// the lens and partially grayed out around it.
	Widget _buildMagnifierScreen() {
	final Color foreground = widget.backgroundColor?.withAlpha(
	(widget.backgroundColor.alpha * _kForegroundScreenOpacityFraction).toInt()
	);

	return IgnorePointer(
	child: Column(
	children: <Widget>[
	Expanded(
	child: Container(
	color: foreground,
	),
	),
	Container(
	decoration: const BoxDecoration(
	border: Border(
	top: BorderSide(width: 0.0, color: _kHighlighterBorder),
	bottom: BorderSide(width: 0.0, color: _kHighlighterBorder),
	)
	),
	constraints: BoxConstraints.expand(
	height: widget.itemExtent * widget.magnification,
	),
	),
	Expanded(
	child: Container(
	color: foreground,
	),
	),
	],
	),
	);
	}

	@override
	Widget build(BuildContext context) {
	Widget result = Stack(
	children: <Widget>[
	Positioned.fill(
	child: ListWheelScrollView.useDelegate(
	controller: widget.scrollController,
	physics: const FixedExtentScrollPhysics(),
	diameterRatio: widget.diameterRatio,
	perspective: _kDefaultPerspective,
	offAxisFraction: widget.offAxisFraction,
	useMagnifier: widget.useMagnifier,
	magnification: widget.magnification,
	itemExtent: widget.itemExtent,
	onSelectedItemChanged: _handleSelectedItemChanged,
	childDelegate: widget.childDelegate,
	),
	),
	_buildGradientScreen(),
	_buildMagnifierScreen(),
	],
	);
	if (widget.backgroundColor != null) {
	result = DecoratedBox(
	decoration: BoxDecoration(
	color: widget.backgroundColor,
	),
	child: result,
	);
	}
	return result;
	}
	}