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// 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 'dart:math' as math;
import 'dart:ui' show window;
import 'package:flutter/foundation.dart';
import 'package:flutter/rendering.dart';
import 'package:flutter/services.dart';
import 'package:flutter/widgets.dart';
import 'package:flutter/material.dart'
hide DropdownButton, DropdownMenuItem, DropdownButtonHideUnderline;
const Duration _kDropdownMenuDuration = Duration(milliseconds: 300);
const double _kMenuItemHeight = kMinInteractiveDimension;
const double _kDenseButtonHeight = 24.0;
const EdgeInsets _kMenuItemPadding = EdgeInsets.symmetric(horizontal: 16.0);
const EdgeInsetsGeometry _kAlignedButtonPadding =
EdgeInsetsDirectional.only(start: 16.0, end: 4.0);
const EdgeInsets _kUnalignedButtonPadding = EdgeInsets.zero;
const EdgeInsets _kAlignedMenuMargin = EdgeInsets.zero;
const EdgeInsetsGeometry _kUnalignedMenuMargin =
EdgeInsetsDirectional.only(start: 16.0, end: 24.0);
typedef DropdownButtonBuilder = List<Widget> Function(BuildContext context);
class _DropdownMenuPainter extends CustomPainter {
_DropdownMenuPainter({
this.color,
this.elevation,
this.selectedIndex,
this.resize,
this.getSelectedItemOffset,
}) : _painter = BoxDecoration(
// If you add an image here, you must provide a real
// configuration in the paint() function and you must provide some sort
// of onChanged callback here.
color: color,
borderRadius: BorderRadius.circular(15.0),
boxShadow: kElevationToShadow[elevation],
).createBoxPainter(),
super(repaint: resize);
final Color color;
final int elevation;
final int selectedIndex;
final Animation<double> resize;
final ValueGetter<double> getSelectedItemOffset;
final BoxPainter _painter;
@override
void paint(Canvas canvas, Size size) {
final double selectedItemOffset = getSelectedItemOffset();
final Tween<double> top = Tween<double>(
begin: selectedItemOffset.clamp(0.0, size.height - _kMenuItemHeight)
as double,
end: 0.0,
);
final Tween<double> bottom = Tween<double>(
begin: (top.begin + _kMenuItemHeight).clamp(_kMenuItemHeight, size.height)
as double,
end: size.height,
);
final Rect rect = Rect.fromLTRB(
0.0, top.evaluate(resize), size.width, bottom.evaluate(resize));
_painter.paint(canvas, rect.topLeft, ImageConfiguration(size: rect.size));
}
@override
bool shouldRepaint(_DropdownMenuPainter oldPainter) {
return oldPainter.color != color ||
oldPainter.elevation != elevation ||
oldPainter.selectedIndex != selectedIndex ||
oldPainter.resize != resize;
}
}
// Do not use the platform-specific default scroll configuration.
// Dropdown menus should never overscroll or display an overscroll indicator.
class _DropdownScrollBehavior extends ScrollBehavior {
const _DropdownScrollBehavior();
@override
TargetPlatform getPlatform(BuildContext context) =>
Theme.of(context).platform;
@override
Widget buildViewportChrome(
BuildContext context, Widget child, AxisDirection axisDirection) =>
child;
@override
ScrollPhysics getScrollPhysics(BuildContext context) =>
const ClampingScrollPhysics();
}
// The widget that is the button wrapping the menu items.
class _DropdownMenuItemButton<T> extends StatefulWidget {
const _DropdownMenuItemButton({
Key key,
@required this.padding,
@required this.route,
@required this.buttonRect,
@required this.constraints,
@required this.itemIndex,
}) : super(key: key);
final _DropdownRoute<T> route;
final EdgeInsets padding;
final Rect buttonRect;
final BoxConstraints constraints;
final int itemIndex;
@override
_DropdownMenuItemButtonState<T> createState() =>
_DropdownMenuItemButtonState<T>();
}
class _DropdownMenuItemButtonState<T>
extends State<_DropdownMenuItemButton<T>> {
void _handleFocusChange(bool focused) {
bool inTraditionalMode;
switch (FocusManager.instance.highlightMode) {
case FocusHighlightMode.touch:
inTraditionalMode = false;
break;
case FocusHighlightMode.traditional:
inTraditionalMode = true;
break;
}
if (focused && inTraditionalMode) {
final _MenuLimits menuLimits = widget.route.getMenuLimits(
widget.buttonRect, widget.constraints.maxHeight, widget.itemIndex);
widget.route.scrollController.animateTo(
menuLimits.scrollOffset,
curve: Curves.easeInOut,
duration: const Duration(milliseconds: 100),
);
}
}
void _handleOnTap() {
final DropdownMenuItem<T> dropdownMenuItem =
widget.route.items[widget.itemIndex].item;
if (dropdownMenuItem.onTap != null) {
dropdownMenuItem.onTap();
}
Navigator.pop(
context,
_DropdownRouteResult<T>(dropdownMenuItem.value),
);
}
static final Map<LogicalKeySet, Intent> _webShortcuts =
<LogicalKeySet, Intent>{
LogicalKeySet(LogicalKeyboardKey.enter): const ActivateIntent(),
};
@override
Widget build(BuildContext context) {
CurvedAnimation opacity;
final double unit = 0.5 / (widget.route.items.length + 1.5);
if (widget.itemIndex == widget.route.selectedIndex) {
opacity = CurvedAnimation(
parent: widget.route.animation, curve: const Threshold(0.0));
} else {
final double start =
(0.5 + (widget.itemIndex + 1) * unit).clamp(0.0, 1.0) as double;
final double end = (start + 1.5 * unit).clamp(0.0, 1.0) as double;
opacity = CurvedAnimation(
parent: widget.route.animation, curve: Interval(start, end));
}
Widget child = FadeTransition(
opacity: opacity,
child: InkWell(
autofocus: widget.itemIndex == widget.route.selectedIndex,
child: Container(
padding: widget.padding,
child: widget.route.items[widget.itemIndex],
),
onTap: _handleOnTap,
onFocusChange: _handleFocusChange,
),
);
if (kIsWeb) {
// On the web, enter doesn't select things, *except* in a <select>
// element, which is what a dropdown emulates.
child = Shortcuts(
shortcuts: _webShortcuts,
child: child,
);
}
return child;
}
}
class _DropdownMenu<T> extends StatefulWidget {
const _DropdownMenu({
Key key,
this.padding,
this.route,
this.buttonRect,
this.constraints,
this.dropdownColor,
}) : super(key: key);
final _DropdownRoute<T> route;
final EdgeInsets padding;
final Rect buttonRect;
final BoxConstraints constraints;
final Color dropdownColor;
@override
_DropdownMenuState<T> createState() => _DropdownMenuState<T>();
}
class _DropdownMenuState<T> extends State<_DropdownMenu<T>> {
CurvedAnimation _fadeOpacity;
CurvedAnimation _resize;
@override
void initState() {
super.initState();
// We need to hold these animations as state because of their curve
// direction. When the route's animation reverses, if we were to recreate
// the CurvedAnimation objects in build, we'd lose
// CurvedAnimation._curveDirection.
_fadeOpacity = CurvedAnimation(
parent: widget.route.animation,
curve: const Interval(0.0, 0.25),
reverseCurve: const Interval(0.75, 1.0),
);
_resize = CurvedAnimation(
parent: widget.route.animation,
curve: const Interval(0.25, 0.5),
reverseCurve: const Threshold(0.0),
);
}
@override
Widget build(BuildContext context) {
// The menu is shown in three stages (unit timing in brackets):
// [0s - 0.25s] - Fade in a rect-sized menu container with the selected item.
// [0.25s - 0.5s] - Grow the otherwise empty menu container from the center
// until it's big enough for as many items as we're going to show.
// [0.5s - 1.0s] Fade in the remaining visible items from top to bottom.
//
// When the menu is dismissed we just fade the entire thing out
// in the first 0.25s.
assert(debugCheckHasMaterialLocalizations(context));
final MaterialLocalizations localizations =
MaterialLocalizations.of(context);
final _DropdownRoute<T> route = widget.route;
final List<Widget> children = <Widget>[
for (int itemIndex = 0; itemIndex < route.items.length; ++itemIndex)
_DropdownMenuItemButton<T>(
route: widget.route,
padding: widget.padding,
buttonRect: widget.buttonRect,
constraints: widget.constraints,
itemIndex: itemIndex,
),
];
return FadeTransition(
opacity: _fadeOpacity,
child: CustomPaint(
painter: _DropdownMenuPainter(
color: widget.dropdownColor ?? Theme.of(context).canvasColor,
elevation: route.elevation,
selectedIndex: route.selectedIndex,
resize: _resize,
// This offset is passed as a callback, not a value, because it must
// be retrieved at paint time (after layout), not at build time.
getSelectedItemOffset: () => route.getItemOffset(route.selectedIndex),
),
child: Semantics(
scopesRoute: true,
namesRoute: true,
explicitChildNodes: true,
label: localizations.popupMenuLabel,
child: Material(
type: MaterialType.transparency,
textStyle: route.style,
child: ScrollConfiguration(
behavior: const _DropdownScrollBehavior(),
child: Scrollbar(
child: ListView(
controller: widget.route.scrollController,
padding: kMaterialListPadding,
shrinkWrap: true,
children: children,
),
),
),
),
),
),
);
}
}
class _DropdownMenuRouteLayout<T> extends SingleChildLayoutDelegate {
_DropdownMenuRouteLayout({
@required this.buttonRect,
@required this.route,
@required this.textDirection,
});
final Rect buttonRect;
final _DropdownRoute<T> route;
final TextDirection textDirection;
@override
BoxConstraints getConstraintsForChild(BoxConstraints constraints) {
// The maximum height of a simple menu should be one or more rows less than
// the view height. This ensures a tappable area outside of the simple menu
// with which to dismiss the menu.
// -- https://material.io/design/components/menus.html#usage
final double maxHeight =
math.max(0.0, constraints.maxHeight - 2 * _kMenuItemHeight);
// The width of a menu should be at most the view width. This ensures that
// the menu does not extend past the left and right edges of the screen.
final double width = math.min(constraints.maxWidth, buttonRect.width);
return BoxConstraints(
minWidth: width,
maxWidth: width,
minHeight: 0.0,
maxHeight: maxHeight,
);
}
@override
Offset getPositionForChild(Size size, Size childSize) {
final _MenuLimits menuLimits =
route.getMenuLimits(buttonRect, size.height, route.selectedIndex);
assert(() {
final Rect container = Offset.zero & size;
if (container.intersect(buttonRect) == buttonRect) {
// If the button was entirely on-screen, then verify
// that the menu is also on-screen.
// If the button was a bit off-screen, then, oh well.
assert(menuLimits.top >= 0.0);
assert(menuLimits.top + menuLimits.height <= size.height);
}
return true;
}());
assert(textDirection != null);
double left;
switch (textDirection) {
case TextDirection.rtl:
left = (buttonRect.right.clamp(0.0, size.width) as double) -
childSize.width;
break;
case TextDirection.ltr:
left =
buttonRect.left.clamp(0.0, size.width - childSize.width) as double;
break;
}
return Offset(left, menuLimits.top);
}
@override
bool shouldRelayout(_DropdownMenuRouteLayout<T> oldDelegate) {
return buttonRect != oldDelegate.buttonRect ||
textDirection != oldDelegate.textDirection;
}
}
// We box the return value so that the return value can be null. Otherwise,
// canceling the route (which returns null) would get confused with actually
// returning a real null value.
@immutable
class _DropdownRouteResult<T> {
const _DropdownRouteResult(this.result);
final T result;
@override
bool operator ==(Object other) {
return other is _DropdownRouteResult<T> && other.result == result;
}
@override
int get hashCode => result.hashCode;
}
class _MenuLimits {
const _MenuLimits(this.top, this.bottom, this.height, this.scrollOffset);
final double top;
final double bottom;
final double height;
final double scrollOffset;
}
class _DropdownRoute<T> extends PopupRoute<_DropdownRouteResult<T>> {
_DropdownRoute({
this.items,
this.padding,
this.buttonRect,
this.selectedIndex,
this.elevation = 8,
this.theme,
@required this.style,
this.barrierLabel,
this.itemHeight,
this.dropdownColor,
}) : assert(style != null),
itemHeights = List<double>.filled(
items.length, itemHeight ?? kMinInteractiveDimension);
final List<_MenuItem<T>> items;
final EdgeInsetsGeometry padding;
final Rect buttonRect;
final int selectedIndex;
final int elevation;
final ThemeData theme;
final TextStyle style;
final double itemHeight;
final Color dropdownColor;
final List<double> itemHeights;
ScrollController scrollController;
@override
Duration get transitionDuration => _kDropdownMenuDuration;
@override
bool get barrierDismissible => true;
@override
Color get barrierColor => null;
@override
final String barrierLabel;
@override
Widget buildPage(BuildContext context, Animation<double> animation,
Animation<double> secondaryAnimation) {
return LayoutBuilder(
builder: (BuildContext context, BoxConstraints constraints) {
return _DropdownRoutePage<T>(
route: this,
constraints: constraints,
items: items,
padding: padding,
buttonRect: buttonRect,
selectedIndex: selectedIndex,
elevation: elevation,
theme: theme,
style: style,
dropdownColor: dropdownColor,
);
});
}
void _dismiss() {
navigator?.removeRoute(this);
}
double getItemOffset(int index) {
double offset = kMaterialListPadding.top;
if (items.isNotEmpty && index > 0) {
assert(items.length == itemHeights?.length);
offset += itemHeights
.sublist(0, index)
.reduce((double total, double height) => total + height);
}
return offset;
}
// Returns the vertical extent of the menu and the initial scrollOffset
// for the ListView that contains the menu items. The vertical center of the
// selected item is aligned with the button's vertical center, as far as
// that's possible given availableHeight.
_MenuLimits getMenuLimits(
Rect buttonRect, double availableHeight, int index) {
final double maxMenuHeight = availableHeight - 2.0 * _kMenuItemHeight;
final double buttonTop = buttonRect.top;
final double buttonBottom = math.min(buttonRect.bottom, availableHeight);
final double selectedItemOffset = getItemOffset(index);
// If the button is placed on the bottom or top of the screen, its top or
// bottom may be less than [_kMenuItemHeight] from the edge of the screen.
// In this case, we want to change the menu limits to align with the top
// or bottom edge of the button.
final double topLimit = math.min(_kMenuItemHeight, buttonTop);
final double bottomLimit =
math.max(availableHeight - _kMenuItemHeight, buttonBottom);
double menuTop = (buttonTop - selectedItemOffset) -
(itemHeights[selectedIndex] - buttonRect.height) / 2.0;
double preferredMenuHeight = kMaterialListPadding.vertical;
if (items.isNotEmpty)
preferredMenuHeight +=
itemHeights.reduce((double total, double height) => total + height);
// If there are too many elements in the menu, we need to shrink it down
// so it is at most the maxMenuHeight.
final double menuHeight = math.min(maxMenuHeight, preferredMenuHeight);
double menuBottom = menuTop + menuHeight;
// If the computed top or bottom of the menu are outside of the range
// specified, we need to bring them into range. If the item height is larger
// than the button height and the button is at the very bottom or top of the
// screen, the menu will be aligned with the bottom or top of the button
// respectively.
if (menuTop < topLimit) menuTop = math.min(buttonTop, topLimit);
if (menuBottom > bottomLimit) {
menuBottom = math.max(buttonBottom, bottomLimit);
menuTop = menuBottom - menuHeight;
}
// If all of the menu items will not fit within availableHeight then
// compute the scroll offset that will line the selected menu item up
// with the select item. This is only done when the menu is first
// shown - subsequently we leave the scroll offset where the user left
// it. This scroll offset is only accurate for fixed height menu items
// (the default).
final double scrollOffset = preferredMenuHeight <= maxMenuHeight
? 0
: math.max(0.0, selectedItemOffset - (buttonTop - menuTop));
return _MenuLimits(menuTop, menuBottom, menuHeight, scrollOffset);
}
}
class _DropdownRoutePage<T> extends StatelessWidget {
const _DropdownRoutePage({
Key key,
this.route,
this.constraints,
this.items,
this.padding,
this.buttonRect,
this.selectedIndex,
this.elevation = 8,
this.theme,
this.style,
this.dropdownColor,
}) : super(key: key);
final _DropdownRoute<T> route;
final BoxConstraints constraints;
final List<_MenuItem<T>> items;
final EdgeInsetsGeometry padding;
final Rect buttonRect;
final int selectedIndex;
final int elevation;
final ThemeData theme;
final TextStyle style;
final Color dropdownColor;
@override
Widget build(BuildContext context) {
assert(debugCheckHasDirectionality(context));
// Computing the initialScrollOffset now, before the items have been laid
// out. This only works if the item heights are effectively fixed, i.e. either
// DropdownButton.itemHeight is specified or DropdownButton.itemHeight is null
// and all of the items' intrinsic heights are less than kMinInteractiveDimension.
// Otherwise the initialScrollOffset is just a rough approximation based on
// treating the items as if their heights were all equal to kMinInteractveDimension.
if (route.scrollController == null) {
final _MenuLimits menuLimits =
route.getMenuLimits(buttonRect, constraints.maxHeight, selectedIndex);
route.scrollController =
ScrollController(initialScrollOffset: menuLimits.scrollOffset);
}
final TextDirection textDirection = Directionality.of(context);
Widget menu = _DropdownMenu<T>(
route: route,
padding: padding.resolve(textDirection),
buttonRect: buttonRect,
constraints: constraints,
dropdownColor: dropdownColor,
);
if (theme != null) menu = Theme(data: theme, child: menu);
return MediaQuery.removePadding(
context: context,
removeTop: true,
removeBottom: true,
removeLeft: true,
removeRight: true,
child: Builder(
builder: (BuildContext context) {
return CustomSingleChildLayout(
delegate: _DropdownMenuRouteLayout<T>(
buttonRect: buttonRect,
route: route,
textDirection: textDirection,
),
child: menu,
);
},
),
);
}
}
// This widget enables _DropdownRoute to look up the sizes of
// each menu item. These sizes are used to compute the offset of the selected
// item so that _DropdownRoutePage can align the vertical center of the
// selected item lines up with the vertical center of the dropdown button,
// as closely as possible.
class _MenuItem<T> extends SingleChildRenderObjectWidget {
const _MenuItem({
Key key,
@required this.onLayout,
@required this.item,
}) : assert(onLayout != null),
super(key: key, child: item);
final ValueChanged<Size> onLayout;
final DropdownMenuItem<T> item;
@override
RenderObject createRenderObject(BuildContext context) {
return _RenderMenuItem(onLayout);
}
@override
void updateRenderObject(
BuildContext context, covariant _RenderMenuItem renderObject) {
renderObject.onLayout = onLayout;
}
}
class _RenderMenuItem extends RenderProxyBox {
_RenderMenuItem(this.onLayout, [RenderBox child])
: assert(onLayout != null),
super(child);
ValueChanged<Size> onLayout;
@override
void performLayout() {
super.performLayout();
onLayout(size);
}
}
// The container widget for a menu item created by a [DropdownButton]. It
// provides the default configuration for [DropdownMenuItem]s, as well as a
// [DropdownButton]'s hint and disabledHint widgets.
class _DropdownMenuItemContainer extends StatelessWidget {
/// Creates an item for a dropdown menu.
///
/// The [child] argument is required.
const _DropdownMenuItemContainer({
Key key,
@required this.child,
}) : assert(child != null),
super(key: key);
/// The widget below this widget in the tree.
///
/// Typically a [Text] widget.
final Widget child;
@override
Widget build(BuildContext context) {
return Container(
constraints: const BoxConstraints(minHeight: _kMenuItemHeight),
alignment: AlignmentDirectional.centerStart,
child: child,
);
}
}
/// An item in a menu created by a [DropdownButton].
///
/// The type `T` is the type of the value the entry represents. All the entries
/// in a given menu must represent values with consistent types.
class DropdownMenuItem<T> extends _DropdownMenuItemContainer {
/// Creates an item for a dropdown menu.
///
/// The [child] argument is required.
const DropdownMenuItem({
Key key,
this.onTap,
this.value,
@required Widget child,
}) : assert(child != null),
super(key: key, child: child);
/// Called when the dropdown menu item is tapped.
final VoidCallback onTap;
/// The value to return if the user selects this menu item.
///
/// Eventually returned in a call to [DropdownButton.onChanged].
final T value;
}
/// An inherited widget that causes any descendant [DropdownButton]
/// widgets to not include their regular underline.
///
/// This is used by [DataTable] to remove the underline from any
/// [DropdownButton] widgets placed within material data tables, as
/// required by the material design specification.
class DropdownButtonHideUnderline extends InheritedWidget {
/// Creates a [DropdownButtonHideUnderline]. A non-null [child] must
/// be given.
const DropdownButtonHideUnderline({
Key key,
@required Widget child,
}) : assert(child != null),
super(key: key, child: child);
/// Returns whether the underline of [DropdownButton] widgets should
/// be hidden.
static bool at(BuildContext context) {
return context.dependOnInheritedWidgetOfExactType<
DropdownButtonHideUnderline>() !=
null;
}
@override
bool updateShouldNotify(DropdownButtonHideUnderline oldWidget) => false;
}
/// A material design button for selecting from a list of items.
///
/// A dropdown button lets the user select from a number of items. The button
/// shows the currently selected item as well as an arrow that opens a menu for
/// selecting another item.
///
/// The type `T` is the type of the [value] that each dropdown item represents.
/// All the entries in a given menu must represent values with consistent types.
/// Typically, an enum is used. Each [DropdownMenuItem] in [items] must be
/// specialized with that same type argument.
///
/// The [onChanged] callback should update a state variable that defines the
/// dropdown's value. It should also call [State.setState] to rebuild the
/// dropdown with the new value.
///
/// {@tool dartpad --template=stateful_widget_scaffold_center}
///
/// This sample shows a `DropdownButton` with a large arrow icon,
/// purple text style, and bold purple underline, whose value is one of "One",
/// "Two", "Free", or "Four".
///
/// ![](https://flutter.github.io/assets-for-api-docs/assets/material/dropdown_button.png)
///
/// ```dart
/// String dropdownValue = 'One';
///
/// @override
/// Widget build(BuildContext context) {
/// return DropdownButton<String>(
/// value: dropdownValue,
/// icon: Icon(Icons.arrow_downward),
/// iconSize: 24,
/// elevation: 16,
/// style: TextStyle(
/// color: Colors.deepPurple
/// ),
/// underline: Container(
/// height: 2,
/// color: Colors.deepPurpleAccent,
/// ),
/// onChanged: (String newValue) {
/// setState(() {
/// dropdownValue = newValue;
/// });
/// },
/// items: <String>['One', 'Two', 'Free', 'Four']
/// .map<DropdownMenuItem<String>>((String value) {
/// return DropdownMenuItem<String>(
/// value: value,
/// child: Text(value),
/// );
/// })
/// .toList(),
/// );
/// }
/// ```
/// {@end-tool}
///
/// If the [onChanged] callback is null or the list of [items] is null
/// then the dropdown button will be disabled, i.e. its arrow will be
/// displayed in grey and it will not respond to input. A disabled button
/// will display the [disabledHint] widget if it is non-null. However, if
/// [disabledHint] is null and [hint] is non-null, the [hint] widget will
/// instead be displayed.
///
/// Requires one of its ancestors to be a [Material] widget.
///
/// See also:
///
/// * [DropdownMenuItem], the class used to represent the [items].
/// * [DropdownButtonHideUnderline], which prevents its descendant dropdown buttons
/// from displaying their underlines.
/// * [RaisedButton], [FlatButton], ordinary buttons that trigger a single action.
/// * <https://material.io/design/components/menus.html#dropdown-menu>
class DropdownButton<T> extends StatefulWidget {
/// Creates a dropdown button.
///
/// The [items] must have distinct values. If [value] isn't null then it
/// must be equal to one of the [DropDownMenuItem] values. If [items] or
/// [onChanged] is null, the button will be disabled, the down arrow
/// will be greyed out, and the [disabledHint] will be shown (if provided).
/// If [disabledHint] is null and [hint] is non-null, [hint] will instead be
/// shown.
///
/// The [elevation] and [iconSize] arguments must not be null (they both have
/// defaults, so do not need to be specified). The boolean [isDense] and
/// [isExpanded] arguments must not be null.
///
/// The [dropdownColor] argument specifies the background color of the
/// dropdown when it is open. If it is null, the current theme's
/// [ThemeData.canvasColor] will be used instead.
DropdownButton({
Key key,
@required this.items,
this.selectedItemBuilder,
this.value,
this.hint,
this.disabledHint,
@required this.onChanged,
this.onTap,
this.elevation = 8,
this.style,
this.underline,
this.icon,
this.iconDisabledColor,
this.iconEnabledColor,
this.iconSize = 24.0,
this.isDense = false,
this.isExpanded = false,
this.itemHeight = kMinInteractiveDimension,
this.focusColor,
this.focusNode,
this.autofocus = false,
this.dropdownColor,
}) : assert(
items == null ||
items.isEmpty ||
value == null ||
items.where((DropdownMenuItem<T> item) {
return item.value == value;
}).length ==
1,
"There should be exactly one item with [DropdownButton]'s value: "
'$value. \n'
'Either zero or 2 or more [DropdownMenuItem]s were detected '
'with the same value',
),
assert(elevation != null),
assert(iconSize != null),
assert(isDense != null),
assert(isExpanded != null),
assert(autofocus != null),
assert(itemHeight == null || itemHeight >= kMinInteractiveDimension),
super(key: key);
/// The list of items the user can select.
///
/// If the [onChanged] callback is null or the list of items is null
/// then the dropdown button will be disabled, i.e. its arrow will be
/// displayed in grey and it will not respond to input. A disabled button
/// will display the [disabledHint] widget if it is non-null. If
/// [disabledHint] is also null but [hint] is non-null, [hint] will instead
/// be displayed.
final List<DropdownMenuItem<T>> items;
/// The value of the currently selected [DropdownMenuItem].
///
/// If [value] is null and [hint] is non-null, the [hint] widget is
/// displayed as a placeholder for the dropdown button's value.
final T value;
/// A placeholder widget that is displayed by the dropdown button.
///
/// If [value] is null, this widget is displayed as a placeholder for
/// the dropdown button's value. This widget is also displayed if the button
/// is disabled ([items] or [onChanged] is null) and [disabledHint] is null.
final Widget hint;
/// A message to show when the dropdown is disabled.
///
/// Displayed if [items] or [onChanged] is null. If [hint] is non-null and
/// [disabledHint] is null, the [hint] widget will be displayed instead.
final Widget disabledHint;
/// {@template flutter.material.dropdownButton.onChanged}
/// Called when the user selects an item.
///
/// If the [onChanged] callback is null or the list of [items] is null
/// then the dropdown button will be disabled, i.e. its arrow will be
/// displayed in grey and it will not respond to input. A disabled button
/// will display the [disabledHint] widget if it is non-null. If
/// [disabledHint] is also null but [hint] is non-null, [hint] will instead
/// be displayed.
/// {@endtemplate}
final ValueChanged<T> onChanged;
/// Called when the dropdown button is tapped.
///
/// This is distinct from [onChanged], which is called when the user
/// selects an item from the dropdown.
///
/// The callback will not be invoked if the dropdown button is disabled.
final VoidCallback onTap;
/// A builder to customize the dropdown buttons corresponding to the
/// [DropdownMenuItem]s in [items].
///
/// When a [DropdownMenuItem] is selected, the widget that will be displayed
/// from the list corresponds to the [DropdownMenuItem] of the same index
/// in [items].
///
/// {@tool dartpad --template=stateful_widget_scaffold}
///
/// This sample shows a `DropdownButton` with a button with [Text] that
/// corresponds to but is unique from [DropdownMenuItem].
///
/// ```dart
/// final List<String> items = <String>['1','2','3'];
/// String selectedItem = '1';
///
/// @override
/// Widget build(BuildContext context) {
/// return Padding(
/// padding: const EdgeInsets.symmetric(horizontal: 12.0),
/// child: DropdownButton<String>(
/// value: selectedItem,
/// onChanged: (String string) => setState(() => selectedItem = string),
/// selectedItemBuilder: (BuildContext context) {
/// return items.map<Widget>((String item) {
/// return Text(item);
/// }).toList();
/// },
/// items: items.map((String item) {
/// return DropdownMenuItem<String>(
/// child: Text('Log $item'),
/// value: item,
/// );
/// }).toList(),
/// ),
/// );
/// }
/// ```
/// {@end-tool}
///
/// If this callback is null, the [DropdownMenuItem] from [items]
/// that matches [value] will be displayed.
final DropdownButtonBuilder selectedItemBuilder;
/// The z-coordinate at which to place the menu when open.
///
/// The following elevations have defined shadows: 1, 2, 3, 4, 6, 8, 9, 12,
/// 16, and 24. See [kElevationToShadow].
///
/// Defaults to 8, the appropriate elevation for dropdown buttons.
final int elevation;
/// The text style to use for text in the dropdown button and the dropdown
/// menu that appears when you tap the button.
///
/// To use a separate text style for selected item when it's displayed within
/// the dropdown button,, consider using [selectedItemBuilder].
///
/// {@tool dartpad --template=stateful_widget_scaffold}
///
/// This sample shows a `DropdownButton` with a dropdown button text style
/// that is different than its menu items.
///
/// ```dart
/// List<String> options = <String>['One', 'Two', 'Free', 'Four'];
/// String dropdownValue = 'One';
///
/// @override
/// Widget build(BuildContext context) {
/// return Container(
/// alignment: Alignment.center,
/// color: Colors.blue,
/// child: DropdownButton<String>(
/// value: dropdownValue,
/// onChanged: (String newValue) {
/// setState(() {
/// dropdownValue = newValue;
/// });
/// },
/// style: TextStyle(color: Colors.blue),
/// selectedItemBuilder: (BuildContext context) {
/// return options.map((String value) {
/// return Text(
/// dropdownValue,
/// style: TextStyle(color: Colors.white),
/// );
/// }).toList();
/// },
/// items: options.map<DropdownMenuItem<String>>((String value) {
/// return DropdownMenuItem<String>(
/// value: value,
/// child: Text(value),
/// );
/// }).toList(),
/// ),
/// );
/// }
/// ```
/// {@end-tool}
///
/// Defaults to the [TextTheme.subtitle1] value of the current
/// [ThemeData.textTheme] of the current [Theme].
final TextStyle style;
/// The widget to use for drawing the drop-down button's underline.
///
/// Defaults to a 0.0 width bottom border with color 0xFFBDBDBD.
final Widget underline;
/// The widget to use for the drop-down button's icon.
///
/// Defaults to an [Icon] with the [Icons.arrow_drop_down] glyph.
final Widget icon;
/// The color of any [Icon] descendant of [icon] if this button is disabled,
/// i.e. if [onChanged] is null.
///
/// Defaults to [Colors.grey.shade400] when the theme's
/// [ThemeData.brightness] is [Brightness.light] and to
/// [Colors.white10] when it is [Brightness.dark]
final Color iconDisabledColor;
/// The color of any [Icon] descendant of [icon] if this button is enabled,
/// i.e. if [onChanged] is defined.
///
/// Defaults to [Colors.grey.shade700] when the theme's
/// [ThemeData.brightness] is [Brightness.light] and to
/// [Colors.white70] when it is [Brightness.dark]
final Color iconEnabledColor;
/// The size to use for the drop-down button's down arrow icon button.
///
/// Defaults to 24.0.
final double iconSize;
/// Reduce the button's height.
///
/// By default this button's height is the same as its menu items' heights.
/// If isDense is true, the button's height is reduced by about half. This
/// can be useful when the button is embedded in a container that adds
/// its own decorations, like [InputDecorator].
final bool isDense;
/// Set the dropdown's inner contents to horizontally fill its parent.
///
/// By default this button's inner width is the minimum size of its contents.
/// If [isExpanded] is true, the inner width is expanded to fill its
/// surrounding container.
final bool isExpanded;
/// If null, then the menu item heights will vary according to each menu item's
/// intrinsic height.
///
/// The default value is [kMinInteractiveDimension], which is also the minimum
/// height for menu items.
///
/// If this value is null and there isn't enough vertical room for the menu,
/// then the menu's initial scroll offset may not align the selected item with
/// the dropdown button. That's because, in this case, the initial scroll
/// offset is computed as if all of the menu item heights were
/// [kMinInteractiveDimension].
final double itemHeight;
/// The color for the button's [Material] when it has the input focus.
final Color focusColor;
/// {@macro flutter.widgets.Focus.focusNode}
final FocusNode focusNode;
/// {@macro flutter.widgets.Focus.autofocus}
final bool autofocus;
/// The background color of the dropdown.
///
/// If it is not provided, the theme's [ThemeData.canvasColor] will be used
/// instead.
final Color dropdownColor;
@override
_DropdownButtonState<T> createState() => _DropdownButtonState<T>();
}
class _DropdownButtonState<T> extends State<DropdownButton<T>>
with WidgetsBindingObserver {
int _selectedIndex;
_DropdownRoute<T> _dropdownRoute;
Orientation _lastOrientation;
FocusNode _internalNode;
FocusNode get focusNode => widget.focusNode ?? _internalNode;
bool _hasPrimaryFocus = false;
Map<Type, Action<Intent>> _actionMap;
FocusHighlightMode _focusHighlightMode;
// Only used if needed to create _internalNode.
FocusNode _createFocusNode() {
return FocusNode(debugLabel: '${widget.runtimeType}');
}
@override
void initState() {
super.initState();
_updateSelectedIndex();
if (widget.focusNode == null) {
_internalNode ??= _createFocusNode();
}
_actionMap = <Type, Action<Intent>>{
ActivateIntent: CallbackAction<ActivateIntent>(
onInvoke: (ActivateIntent intent) => _handleTap(),
),
};
focusNode.addListener(_handleFocusChanged);
final FocusManager focusManager = WidgetsBinding.instance.focusManager;
_focusHighlightMode = focusManager.highlightMode;
focusManager.addHighlightModeListener(_handleFocusHighlightModeChange);
}
@override
void dispose() {
WidgetsBinding.instance.removeObserver(this);
_removeDropdownRoute();
WidgetsBinding.instance.focusManager
.removeHighlightModeListener(_handleFocusHighlightModeChange);
focusNode.removeListener(_handleFocusChanged);
_internalNode?.dispose();
super.dispose();
}
void _removeDropdownRoute() {
_dropdownRoute?._dismiss();
_dropdownRoute = null;
_lastOrientation = null;
}
void _handleFocusChanged() {
if (_hasPrimaryFocus != focusNode.hasPrimaryFocus) {
setState(() {
_hasPrimaryFocus = focusNode.hasPrimaryFocus;
});
}
}
void _handleFocusHighlightModeChange(FocusHighlightMode mode) {
if (!mounted) {
return;
}
setState(() {
_focusHighlightMode = mode;
});
}
@override
void didUpdateWidget(DropdownButton<T> oldWidget) {
super.didUpdateWidget(oldWidget);
if (widget.focusNode != oldWidget.focusNode) {
oldWidget.focusNode?.removeListener(_handleFocusChanged);
if (widget.focusNode == null) {
_internalNode ??= _createFocusNode();
}
_hasPrimaryFocus = focusNode.hasPrimaryFocus;
focusNode.addListener(_handleFocusChanged);
}
_updateSelectedIndex();
}
void _updateSelectedIndex() {
if (!_enabled) {
return;
}
assert(widget.value == null ||
widget.items
.where((DropdownMenuItem<T> item) => item.value == widget.value)
.length ==
1);
_selectedIndex = null;
for (int itemIndex = 0; itemIndex < widget.items.length; itemIndex++) {
if (widget.items[itemIndex].value == widget.value) {
_selectedIndex = itemIndex;
return;
}
}
}
TextStyle get _textStyle =>
widget.style ?? Theme.of(context).textTheme.subtitle1;
void _handleTap() {
final RenderBox itemBox = context.findRenderObject() as RenderBox;
final Rect itemRect = itemBox.localToGlobal(Offset.zero) & itemBox.size;
final TextDirection textDirection = Directionality.of(context);
final EdgeInsetsGeometry menuMargin =
ButtonTheme.of(context).alignedDropdown
? _kAlignedMenuMargin
: _kUnalignedMenuMargin;
final List<_MenuItem<T>> menuItems =
List<_MenuItem<T>>(widget.items.length);
for (int index = 0; index < widget.items.length; index += 1) {
menuItems[index] = _MenuItem<T>(
item: widget.items[index],
onLayout: (Size size) {
// If [_dropdownRoute] is null and onLayout is called, this means
// that performLayout was called on a _DropdownRoute that has not
// left the widget tree but is already on its way out.
//
// Since onLayout is used primarily to collect the desired heights
// of each menu item before laying them out, not having the _DropdownRoute
// collect each item's height to lay out is fine since the route is
// already on its way out.
if (_dropdownRoute == null) return;
_dropdownRoute.itemHeights[index] = size.height;
},
);
}
assert(_dropdownRoute == null);
_dropdownRoute = _DropdownRoute<T>(
items: menuItems,
buttonRect: menuMargin.resolve(textDirection).inflateRect(itemRect),
padding: _kMenuItemPadding.resolve(textDirection),
selectedIndex: _selectedIndex ?? 0,
elevation: widget.elevation,
theme: Theme.of(context, shadowThemeOnly: true),
style: _textStyle,
barrierLabel: MaterialLocalizations.of(context).modalBarrierDismissLabel,
itemHeight: widget.itemHeight,
dropdownColor: widget.dropdownColor,
);
Navigator.push(context, _dropdownRoute)
.then<void>((_DropdownRouteResult<T> newValue) {
_removeDropdownRoute();
if (!mounted || newValue == null) return;
if (widget.onChanged != null) widget.onChanged(newValue.result);
});
if (widget.onTap != null) {
widget.onTap();
}
}
// When isDense is true, reduce the height of this button from _kMenuItemHeight to
// _kDenseButtonHeight, but don't make it smaller than the text that it contains.
// Similarly, we don't reduce the height of the button so much that its icon
// would be clipped.
double get _denseButtonHeight {
final double fontSize =
_textStyle.fontSize ?? Theme.of(context).textTheme.subtitle1.fontSize;
return math.max(fontSize, math.max(widget.iconSize, _kDenseButtonHeight));
}
Color get _iconColor {
// These colors are not defined in the Material Design spec.
if (_enabled) {
if (widget.iconEnabledColor != null) return widget.iconEnabledColor;
switch (Theme.of(context).brightness) {
case Brightness.light:
return Colors.grey.shade700;
case Brightness.dark:
return Colors.white70;
}
} else {
if (widget.iconDisabledColor != null) return widget.iconDisabledColor;
switch (Theme.of(context).brightness) {
case Brightness.light:
return Colors.grey.shade400;
case Brightness.dark:
return Colors.white10;
}
}
assert(false);
return null;
}
bool get _enabled =>
widget.items != null &&
widget.items.isNotEmpty &&
widget.onChanged != null;
Orientation _getOrientation(BuildContext context) {
Orientation result = MediaQuery.of(context, nullOk: true)?.orientation;
if (result == null) {
// If there's no MediaQuery, then use the window aspect to determine
// orientation.
final Size size = window.physicalSize;
result = size.width > size.height
? Orientation.landscape
: Orientation.portrait;
}
return result;
}
bool get _showHighlight {
switch (_focusHighlightMode) {
case FocusHighlightMode.touch:
return false;
case FocusHighlightMode.traditional:
return _hasPrimaryFocus;
}
return null;
}
@override
Widget build(BuildContext context) {
assert(debugCheckHasMaterial(context));
assert(debugCheckHasMaterialLocalizations(context));
final Orientation newOrientation = _getOrientation(context);
_lastOrientation ??= newOrientation;
if (newOrientation != _lastOrientation) {
_removeDropdownRoute();
_lastOrientation = newOrientation;
}
// The width of the button and the menu are defined by the widest
// item and the width of the hint.
List<Widget> items;
if (_enabled) {
items = widget.selectedItemBuilder == null
? List<Widget>.from(widget.items)
: widget.selectedItemBuilder(context);
} else {
items = widget.selectedItemBuilder == null
? <Widget>[]
: widget.selectedItemBuilder(context);
}
int hintIndex;
if (widget.hint != null || (!_enabled && widget.disabledHint != null)) {
Widget displayedHint =
_enabled ? widget.hint : widget.disabledHint ?? widget.hint;
if (widget.selectedItemBuilder == null)
displayedHint = _DropdownMenuItemContainer(child: displayedHint);
hintIndex = items.length;
items.add(DefaultTextStyle(
style: _textStyle.copyWith(color: Theme.of(context).hintColor),
child: IgnorePointer(
ignoringSemantics: false,
child: displayedHint,
),
));
}
final EdgeInsetsGeometry padding = ButtonTheme.of(context).alignedDropdown
? _kAlignedButtonPadding
: _kUnalignedButtonPadding;
// If value is null (then _selectedIndex is null) or if disabled then we
// display the hint or nothing at all.
final int index = _enabled ? (_selectedIndex ?? hintIndex) : hintIndex;
Widget innerItemsWidget;
if (items.isEmpty) {
innerItemsWidget = Container();
} else {
innerItemsWidget = IndexedStack(
index: index,
alignment: AlignmentDirectional.centerStart,
children: widget.isDense
? items
: items.map((Widget item) {
return widget.itemHeight != null
? SizedBox(height: widget.itemHeight, child: item)
: Column(
mainAxisSize: MainAxisSize.min,
children: <Widget>[item]);
}).toList(),
);
}
const Icon defaultIcon = Icon(Icons.arrow_drop_down);
Widget result = DefaultTextStyle(
style: _textStyle,
child: Container(
decoration: _showHighlight
? BoxDecoration(
color: widget.focusColor ?? Theme.of(context).focusColor,
borderRadius: const BorderRadius.all(Radius.circular(4.0)),
)
: null,
padding: padding.resolve(Directionality.of(context)),
height: widget.isDense ? _denseButtonHeight : null,
child: Row(
mainAxisAlignment: MainAxisAlignment.spaceBetween,
mainAxisSize: MainAxisSize.min,
children: <Widget>[
if (widget.isExpanded)
Expanded(child: innerItemsWidget)
else
innerItemsWidget,
IconTheme(
data: IconThemeData(
color: _iconColor,
size: widget.iconSize,
),
child: widget.icon ?? defaultIcon,
),
],
),
),
);
if (!DropdownButtonHideUnderline.at(context)) {
final double bottom =
(widget.isDense || widget.itemHeight == null) ? 0.0 : 8.0;
result = Stack(
children: <Widget>[
result,
Positioned(
left: 0.0,
right: 0.0,
bottom: bottom,
child: widget.underline ??
Container(
height: 1.0,
decoration: const BoxDecoration(
border: Border(
bottom: BorderSide(
color: Color(0xFFBDBDBD),
width: 0.0,
),
),
),
),
),
],
);
}
return Semantics(
button: true,
child: Actions(
actions: _actionMap,
child: Focus(
canRequestFocus: _enabled,
focusNode: focusNode,
autofocus: widget.autofocus,
child: GestureDetector(
onTap: _enabled ? _handleTap : null,
behavior: HitTestBehavior.opaque,
child: result,
),
),
),
);
}
}
/// A convenience widget that wraps a [DropdownButton] in a [FormField].
class DropdownButtonFormField<T> extends FormField<T> {
/// Creates a [DropdownButton] widget wrapped in an [InputDecorator] and
/// [FormField].
///
/// The [DropdownButton] [items] parameters must not be null.
DropdownButtonFormField({
Key key,
T value,
@required List<DropdownMenuItem<T>> items,
DropdownButtonBuilder selectedItemBuilder,
Widget hint,
@required this.onChanged,
VoidCallback onTap,
this.decoration = const InputDecoration(),
FormFieldSetter<T> onSaved,
FormFieldValidator<T> validator,
bool autovalidate = false,
Widget disabledHint,
int elevation = 8,
TextStyle style,
Widget icon,
Color iconDisabledColor,
Color iconEnabledColor,
double iconSize = 24.0,
bool isDense = true,
bool isExpanded = false,
double itemHeight,
}) : assert(
items == null ||
items.isEmpty ||
value == null ||
items.where((DropdownMenuItem<T> item) {
return item.value == value;
}).length ==
1,
"There should be exactly one item with [DropdownButton]'s value: "
'$value. \n'
'Either zero or 2 or more [DropdownMenuItem]s were detected '
'with the same value',
),
assert(decoration != null),
assert(elevation != null),
assert(iconSize != null),
assert(isDense != null),
assert(isExpanded != null),
assert(itemHeight == null || itemHeight > 0),
super(
key: key,
onSaved: onSaved,
initialValue: value,
validator: validator,
autovalidate: autovalidate,
builder: (FormFieldState<T> field) {
final _DropdownButtonFormFieldState<T> state =
field as _DropdownButtonFormFieldState<T>;
final InputDecoration effectiveDecoration =
decoration.applyDefaults(
Theme.of(field.context).inputDecorationTheme,
);
return InputDecorator(
decoration:
effectiveDecoration.copyWith(errorText: field.errorText),
isEmpty: state.value == null,
child: DropdownButtonHideUnderline(
child: DropdownButton<T>(
value: state.value,
items: items,
selectedItemBuilder: selectedItemBuilder,
hint: hint,
onChanged: onChanged == null ? null : state.didChange,
onTap: onTap,
disabledHint: disabledHint,
elevation: elevation,
style: style,
icon: icon,
iconDisabledColor: iconDisabledColor,
iconEnabledColor: iconEnabledColor,
iconSize: iconSize,
isDense: isDense,
isExpanded: isExpanded,
itemHeight: itemHeight,
),
),
);
},
);
/// {@macro flutter.material.dropdownButton.onChanged}
final ValueChanged<T> onChanged;
/// The decoration to show around the dropdown button form field.
///
/// By default, draws a horizontal line under the dropdown button field but can be
/// configured to show an icon, label, hint text, and error text.
///
/// Specify null to remove the decoration entirely (including the
/// extra padding introduced by the decoration to save space for the labels).
final InputDecoration decoration;
@override
FormFieldState<T> createState() => _DropdownButtonFormFieldState<T>();
}
class _DropdownButtonFormFieldState<T> extends FormFieldState<T> {
@override
DropdownButtonFormField<T> get widget =>
super.widget as DropdownButtonFormField<T>;
@override
void didChange(T value) {
super.didChange(value);
assert(widget.onChanged != null);
widget.onChanged(value);
}
}
import 'package:flutter/material.dart'
hide DropdownButton, DropdownMenuItem, DropdownButtonHideUnderline;
import 'my_dropdown.dart';
void main() => runApp(App());
class App extends StatefulWidget {
const App({Key key}) : super(key: key);
@override
_AppState createState() => _AppState();
}
class _AppState extends State<App> {
String selectedValue;
@override
Widget build(BuildContext context) {
return MaterialApp(
home: Scaffold(
body: Center(
child: Container(
width: 200,
child: DropdownButtonHideUnderline(
child: DropdownButton<String>(
style: TextStyle(
fontWeight: FontWeight.w600,
fontSize: 18,
color: Colors.black,
),
isExpanded: true,
value: selectedValue, //var that
items: [
DropdownMenuItem(child: Text('Apple')),
DropdownMenuItem(child: Text('Google')),
DropdownMenuItem(child: Text('Samsung')),
DropdownMenuItem(child: Text('Sony')),
DropdownMenuItem(child: Text('LG')),
], //simple function that holds the values of all the items
onChanged: (String value) {
setState(() {
selectedValue = value;
});
},
),
),
),
),
),
);
}
}
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