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遗憾的是，我还没有找到 Flutter 提供的任何选项或可能性来实现一轮 SnackBar。
如果您真的需要/想要圆角和间距，您可以复制SnackBar 的源代码并对副本进行调整。请记住将implements SnackBar 添加到您的类定义中。
我已经开始实施并添加了圆角。您只需为 iPhone X 等手机添加底部填充，它们的底部有元素，会遮挡视图。 （要获得底部间距，您可以使用MediaQuery.of(context).viewInsets.bottom。）
您可以复制的独立示例：
main.dart
import 'package:flutter/material.dart';
import 'package:your_app_name/my_snack.dart';
void main() => runApp(MyApp());
class MyApp extends StatelessWidget {
@override
Widget build(BuildContext context) {
return MaterialApp(
home: Scaffold(
body: MyBody()
),
);
}
}
class MyBody extends StatelessWidget {
@override
Widget build(BuildContext context) {
return Center(
child: RaisedButton(onPressed: () {
Scaffold.of(context).showSnackBar(MySnack(content: Text('MySnack!')));
}),
);
}
}
my_snack.dart
// Copyright 2015 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/rendering.dart';
import 'package:flutter/widgets.dart';
import 'package:flutter/material.dart';
const double _kSnackBarPadding = 24.0;
const double _kSingleLineVerticalPadding = 14.0;
const Color _kSnackBackground = Color(0xFF323232);
// TODO(ianh): We should check if the given text and actions are going to fit on
// one line or not, and if they are, use the single-line layout, and if not, use
// the multiline layout. See link above.
// TODO(ianh): Implement the Tablet version of snackbar if we're "on a tablet".
const Duration _kSnackBarTransitionDuration = Duration(milliseconds: 250);
const Duration _kSnackBarDisplayDuration = Duration(milliseconds: 4000);
const Curve _snackBarHeightCurve = Curves.fastOutSlowIn;
const Curve _snackBarFadeCurve = Interval(0.72, 1.0, curve: Curves.fastOutSlowIn);
/// Specify how a [SnackBar] was closed.
///
/// The [ScaffoldState.showSnackBar] function returns a
/// [ScaffoldFeatureController]. The value of the controller's closed property
/// is a Future that resolves to a SnackBarClosedReason. Applications that need
/// to know how a snackbar was closed can use this value.
///
/// Example:
///
/// ```dart
/// Scaffold.of(context).showSnackBar(
/// SnackBar( ... )
/// ).closed.then((SnackBarClosedReason reason) {
/// ...
/// });
/// ```
/// A button for a [SnackBar], known as an "action".
///
/// Snack bar actions are always enabled. If you want to disable a snack bar
/// action, simply don't include it in the snack bar.
///
/// Snack bar actions can only be pressed once. Subsequent presses are ignored.
///
/// See also:
///
/// * [SnackBar]
/// * <https://material.io/design/components/snackbars.html>
class _SnackBarActionState extends State<SnackBarAction> {
bool _haveTriggeredAction = false;
void _handlePressed() {
if (_haveTriggeredAction)
return;
setState(() {
_haveTriggeredAction = true;
});
widget.onPressed();
Scaffold.of(context).hideCurrentSnackBar(reason: SnackBarClosedReason.action);
}
@override
Widget build(BuildContext context) {
return FlatButton(
onPressed: _haveTriggeredAction ? null : _handlePressed,
child: Text(widget.label),
textColor: widget.textColor,
disabledTextColor: widget.disabledTextColor,
);
}
}
/// A lightweight message with an optional action which briefly displays at the
/// bottom of the screen.
///
/// To display a snack bar, call `Scaffold.of(context).showSnackBar()`, passing
/// an instance of [SnackBar] that describes the message.
///
/// To control how long the [SnackBar] remains visible, specify a [duration].
///
/// A SnackBar with an action will not time out when TalkBack or VoiceOver are
/// enabled. This is controlled by [AccessibilityFeatures.accessibleNavigation].
///
/// See also:
///
/// * [Scaffold.of], to obtain the current [ScaffoldState], which manages the
/// display and animation of snack bars.
/// * [ScaffoldState.showSnackBar], which displays a [SnackBar].
/// * [ScaffoldState.removeCurrentSnackBar], which abruptly hides the currently
/// displayed snack bar, if any, and allows the next to be displayed.
/// * [SnackBarAction], which is used to specify an [action] button to show
/// on the snack bar.
/// * <https://material.io/design/components/snackbars.html>
class MySnack extends StatelessWidget implements SnackBar {
/// Creates a snack bar.
///
/// The [content] argument must be non-null.
const MySnack({
Key key,
@required this.content,
this.backgroundColor,
this.action,
this.duration = _kSnackBarDisplayDuration,
this.animation,
}) : assert(content != null),
assert(duration != null),
super(key: key);
/// The primary content of the snack bar.
///
/// Typically a [Text] widget.
final Widget content;
/// The Snackbar's background color. By default the color is dark grey.
final Color backgroundColor;
/// (optional) An action that the user can take based on the snack bar.
///
/// For example, the snack bar might let the user undo the operation that
/// prompted the snackbar. Snack bars can have at most one action.
///
/// The action should not be "dismiss" or "cancel".
final SnackBarAction action;
/// The amount of time the snack bar should be displayed.
///
/// Defaults to 4.0s.
///
/// See also:
///
/// * [ScaffoldState.removeCurrentSnackBar], which abruptly hides the
/// currently displayed snack bar, if any, and allows the next to be
/// displayed.
/// * <https://material.io/design/components/snackbars.html>
final Duration duration;
/// The animation driving the entrance and exit of the snack bar.
final Animation<double> animation;
@override
Widget build(BuildContext context) {
final MediaQueryData mediaQueryData = MediaQuery.of(context);
assert(animation != null);
final ThemeData theme = Theme.of(context);
final ThemeData darkTheme = ThemeData(
brightness: Brightness.dark,
accentColor: theme.accentColor,
accentColorBrightness: theme.accentColorBrightness,
);
final List<Widget> children = <Widget>[
const SizedBox(width: _kSnackBarPadding),
Expanded(
child: Container(
padding: const EdgeInsets.symmetric(vertical: _kSingleLineVerticalPadding),
child: DefaultTextStyle(
style: darkTheme.textTheme.subhead,
child: content,
),
),
),
];
if (action != null) {
children.add(ButtonTheme.bar(
padding: const EdgeInsets.symmetric(horizontal: _kSnackBarPadding),
textTheme: ButtonTextTheme.accent,
child: action,
));
} else {
children.add(const SizedBox(width: _kSnackBarPadding));
}
final CurvedAnimation heightAnimation = CurvedAnimation(parent: animation, curve: _snackBarHeightCurve);
final CurvedAnimation fadeAnimation = CurvedAnimation(parent: animation, curve: _snackBarFadeCurve, reverseCurve: const Threshold(0.0));
Widget snackbar = SafeArea(
bottom: false,
top: false,
child: Row(
children: children,
crossAxisAlignment: CrossAxisAlignment.center,
),
);
snackbar = Semantics(
container: true,
liveRegion: true,
onDismiss: () {
Scaffold.of(context).removeCurrentSnackBar(reason: SnackBarClosedReason.dismiss);
},
child: Dismissible(
key: const Key('dismissible'),
direction: DismissDirection.down,
resizeDuration: null,
onDismissed: (DismissDirection direction) {
Scaffold.of(context).removeCurrentSnackBar(reason: SnackBarClosedReason.swipe);
},
child: Padding(
padding: const EdgeInsets.all(8.0),
child: Container(
decoration: BoxDecoration(
color: backgroundColor ?? _kSnackBackground,
borderRadius: BorderRadius.circular(8.0)
),
child: Material(
elevation: 6.0,
color: Colors.transparent,
child: Theme(
data: darkTheme,
child: mediaQueryData.accessibleNavigation ? snackbar : FadeTransition(
opacity: fadeAnimation,
child: snackbar,
),
),
),
),
),
),
);
return ClipRect(
child: mediaQueryData.accessibleNavigation ? snackbar : AnimatedBuilder(
animation: heightAnimation,
builder: (BuildContext context, Widget child) {
return Align(
alignment: AlignmentDirectional.topStart,
heightFactor: heightAnimation.value,
child: child,
);
},
child: snackbar,
),
);
}
// API for Scaffold.addSnackBar():
/// Creates an animation controller useful for driving a snack bar's entrance and exit animation.
static AnimationController createAnimationController({ @required TickerProvider vsync }) {
return AnimationController(
duration: _kSnackBarTransitionDuration,
debugLabel: 'SnackBar',
vsync: vsync,
);
}
/// Creates a copy of this snack bar but with the animation replaced with the given animation.
///
/// If the original snack bar lacks a key, the newly created snack bar will
/// use the given fallback key.
SnackBar withAnimation(Animation<double> newAnimation, { Key fallbackKey }) {
return MySnack(
key: key ?? fallbackKey,
content: content,
backgroundColor: backgroundColor,
action: action,
duration: duration,
animation: newAnimation,
);
}
}
对 SnackBar 所做的更改：
- 将
SnackBar重命名为MySnack
- 将
implements SnackBar 添加到MySnack 类
- 在
MySnack构建方法中的SafeArea中设置bottom: false
- 在
Material 周围添加了Container，这是SnackBar 的背景
- 将
color 声明从Material 移动到创建的Container
- 将所需的
borderRadius（连同color）作为BoxDecoration 添加到Container