appBar: new AppBar(
leading: getAppBarLeading(context),
SRC：
// 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/material.dart';
const double _kLeadingWidth =
kToolbarHeight; // So the leading button is square.
/// A "back" icon that's appropriate for the current [TargetPlatform].
///
/// The current platform is determined by querying for the ambient [Theme].
///
/// See also:
///
/// * [BackButton], an [IconButton] with a [BackButtonIcon] that calls
/// [Navigator.maybePop] to return to the previous route.
/// * [IconButton], which is a more general widget for creating buttons
/// with icons.
/// * [Icon], a material design icon.
/// * [ThemeData.platform], which specifies the current platform.
class BackButtonIcon2 extends StatelessWidget {
/// Creates an icon that shows the appropriate "back" image for
/// the current platform (as obtained from the [Theme]).
const BackButtonIcon2({Key key}) : super(key: key);
/// Returns the appropriate "back" icon for the given `platform`.
static IconData _getIconData(
TargetPlatform platform, TextDirection direction) {
switch (platform) {
case TargetPlatform.android:
case TargetPlatform.fuchsia:
return (direction == TextDirection.rtl)
? Icons.arrow_forward
: Icons.arrow_back;
case TargetPlatform.iOS:
return (direction == TextDirection.rtl)
? Icons.arrow_forward_ios
: Icons.arrow_back_ios;
}
assert(false);
return null;
}
@override
Widget build(BuildContext context) => new Icon(_getIconData(
Theme.of(context).platform,
Directionality.of(context),
));
}
/// A material design back button.
///
/// A [BackButton] is an [IconButton] with a "back" icon appropriate for the
/// current [TargetPlatform]. When pressed, the back button calls
/// [Navigator.maybePop] to return to the previous route.
///
/// When deciding to display a [BackButton], consider using
/// `ModalRoute.of(context)?.canPop` to check whether the current route can be
/// popped. If that value is false (e.g., because the current route is the
/// initial route), the [BackButton] will not have any effect when pressed,
/// which could frustrate the user.
///
/// Requires one of its ancestors to be a [Material] widget.
///
/// See also:
///
/// * [AppBar], which automatically uses a [BackButton] in its
/// [AppBar.leading] slot when the [Scaffold] has no [Drawer] and the
/// current [Route] is not the [Navigator]'s first route.
/// * [BackButtonIcon], which is useful if you need to create a back button
/// that responds differently to being pressed.
/// * [IconButton], which is a more general widget for creating buttons with
/// icons.
/// * [CloseButton], an alternative which may be more appropriate for leaf
/// node pages in the navigation tree.
class BackButton2 extends StatelessWidget {
/// Creates an [IconButton] with the appropriate "back" icon for the current
/// target platform.
const BackButton2({Key key, this.color}) : super(key: key);
/// The color to use for the icon.
///
/// Defaults to the [IconThemeData.color] specified in the ambient [IconTheme],
/// which usually matches the ambient [Theme]'s [ThemeData.iconTheme].
final Color color;
@override
Widget build(BuildContext context) {
return new IconButton(
icon: const BackButtonIcon2(),
color: color,
tooltip: MaterialLocalizations.of(context).backButtonTooltip,
onPressed: () {
Navigator.of(context).maybePop();
});
}
}
/// A material design close button.
///
/// A [CloseButton] is an [IconButton] with a "close" icon. When pressed, the
/// close button calls [Navigator.maybePop] to return to the previous route.
///
/// Use a [CloseButton] instead of a [BackButton] on fullscreen dialogs or
/// pages that may solicit additional actions to close.
///
/// See also:
///
/// * [AppBar], which automatically uses a [CloseButton] in its
/// [AppBar.leading] slot when appropriate.
/// * [BackButton], which is more appropriate for middle nodes in the
/// navigation tree or where pages can be popped instantaneously with
/// no user data consequence.
/// * [IconButton], to create other material design icon buttons.
class CloseButton2 extends StatelessWidget {
/// Creates a Material Design close button.
const CloseButton2({Key key}) : super(key: key);
@override
Widget build(BuildContext context) {
return new IconButton(
icon: const Icon(Icons.close),
tooltip: MaterialLocalizations.of(context).closeButtonTooltip,
onPressed: () {
Navigator.of(context).maybePop();
},
);
}
}
Widget getAppBarLeading(BuildContext context) {
final ModalRoute<dynamic> parentRoute = ModalRoute.of(context);
final bool canPop = parentRoute?.canPop ?? false;
final bool useCloseButton =
parentRoute is MaterialPageRoute<dynamic> && parentRoute.fullscreenDialog;
Widget leading = canPop
? (useCloseButton ? const CloseButton2() : const BackButton2())
: null;
if (leading != null) {
leading = new ConstrainedBox(
constraints: const BoxConstraints.tightFor(width: _kLeadingWidth),
child: leading,
);
}
return leading;
}
1 回答
UPDATE
Flutter now handles directionality for icons.
我已经阅读了源代码，BackButton现在没有考虑Directionality .
所以我创建了自己的BackButton2和getAppBarLeading函数
SRC：