packages/flutter/lib/src/material/page.dart

// 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.

// @dart = 2.8

import 'package:flutter/cupertino.dart';
import 'package:flutter/widgets.dart';

import 'page_transitions_theme.dart';
import 'theme.dart';

/// A modal route that replaces the entire screen with a platform-adaptive
/// transition.
///
/// {@macro flutter.material.materialRouteTransitionMixin}
///
/// By default, when a modal route is replaced by another, the previous route
/// remains in memory. To free all the resources when this is not necessary, set
/// [maintainState] to false.
///
/// The `fullscreenDialog` property specifies whether the incoming route is a
/// fullscreen modal dialog. On iOS, those routes animate from the bottom to the
/// top rather than horizontally.
///
/// The type `T` specifies the return type of the route which can be supplied as
/// the route is popped from the stack via [Navigator.pop] by providing the
/// optional `result` argument.
///
/// See also:
///
///  * [MaterialRouteTransitionMixin], which provides the material transition
///    for this route.
///  * [MaterialPage], which is a [Page] of this class.
class MaterialPageRoute<T> extends PageRoute<T> with MaterialRouteTransitionMixin<T> {
  /// Construct a MaterialPageRoute whose contents are defined by [builder].
  ///
  /// The values of [builder], [maintainState], and [PageRoute.fullscreenDialog]
  /// must not be null.
  MaterialPageRoute({
    @required this.builder,
    RouteSettings settings,
    this.maintainState = true,
    bool fullscreenDialog = false,
  }) : assert(builder != null),
       assert(maintainState != null),
       assert(fullscreenDialog != null),
       assert(opaque),
       super(settings: settings, fullscreenDialog: fullscreenDialog);

  /// Builds the primary contents of the route.
  final WidgetBuilder builder;

  @override
  Widget buildContent(BuildContext context) => builder(context);

  @override
  final bool maintainState;

  @override
  String get debugLabel => '${super.debugLabel}(${settings.name})';
}


/// A mixin that provides platform-adaptive transitions for a [PageRoute].
///
/// {@template flutter.material.materialRouteTransitionMixin}
/// For Android, the entrance transition for the page slides the route upwards
/// and fades it in. The exit transition is the same, but in reverse.
///
/// The transition is adaptive to the platform and on iOS, the route slides in
/// from the right and exits in reverse. The route also shifts to the left in
/// parallax when another page enters to cover it. (These directions are flipped
/// in environments with a right-to-left reading direction.)
/// {@endtemplate}
///
/// See also:
///
///  * [PageTransitionsTheme], which defines the default page transitions used
///    by the [MaterialRouteTransitionMixin.buildTransitions].
mixin MaterialRouteTransitionMixin<T> on PageRoute<T> {
  /// Builds the primary contents of the route.
  @protected
  Widget buildContent(BuildContext context);

  @override
  Duration get transitionDuration => const Duration(milliseconds: 300);

  @override
  Color get barrierColor => null;

  @override
  String get barrierLabel => null;

  @override
  bool canTransitionTo(TransitionRoute<dynamic> nextRoute) {
    // Don't perform outgoing animation if the next route is a fullscreen dialog.
    return (nextRoute is MaterialRouteTransitionMixin && !nextRoute.fullscreenDialog)
      || (nextRoute is CupertinoRouteTransitionMixin && !nextRoute.fullscreenDialog);
  }

  @override
  Widget buildPage(
    BuildContext context,
    Animation<double> animation,
    Animation<double> secondaryAnimation,
  ) {
    final Widget result = buildContent(context);
    assert(() {
      if (result == null) {
        throw FlutterError(
          'The builder for route "${settings.name}" returned null.\n'
          'Route builders must never return null.'
        );
      }
      return true;
    }());
    return Semantics(
      scopesRoute: true,
      explicitChildNodes: true,
      child: result,
    );
  }

  @override
  Widget buildTransitions(BuildContext context, Animation<double> animation, Animation<double> secondaryAnimation, Widget child) {
    final PageTransitionsTheme theme = Theme.of(context).pageTransitionsTheme;
    return theme.buildTransitions<T>(this, context, animation, secondaryAnimation, child);
  }
}

/// A page that creates a material style [PageRoute].
///
/// {@macro flutter.material.materialRouteTransitionMixin}
///
/// By default, when the created route is replaced by another, the previous
/// route remains in memory. To free all the resources when this is not
/// necessary, set [maintainState] to false.
///
/// The `fullscreenDialog` property specifies whether the created route is a
/// fullscreen modal dialog. On iOS, those routes animate from the bottom to the
/// top rather than horizontally.
///
/// The type `T` specifies the return type of the route which can be supplied as
/// the route is popped from the stack via [Navigator.transitionDelegate] by
/// providing the optional `result` argument to the
/// [RouteTransitionRecord.markForPop] in the [TransitionDelegate.resolve].
///
/// See also:
///
///  * [MaterialPageRoute], which is the [PageRoute] version of this class
class MaterialPage<T> extends Page<T> {
  /// Creates a material page.
  const MaterialPage({
    @required this.child,
    this.maintainState = true,
    this.fullscreenDialog = false,
    LocalKey key,
    String name,
    Object arguments,
  }) : assert(child != null),
       assert(maintainState != null),
       assert(fullscreenDialog != null),
       super(key: key, name: name, arguments: arguments);

  /// The content to be shown in the [Route] created by this page.
  final Widget child;

  /// {@macro flutter.widgets.modalRoute.maintainState}
  final bool maintainState;

  /// {@macro flutter.widgets.pageRoute.fullscreenDialog}
  final bool fullscreenDialog;

  @override
  Route<T> createRoute(BuildContext context) {
    return _PageBasedMaterialPageRoute<T>(page: this);
  }
}

// A page-based version of MaterialPageRoute.
//
// This route uses the builder from the page to build its content. This ensures
// the content is up to date after page updates.
class _PageBasedMaterialPageRoute<T> extends PageRoute<T> with MaterialRouteTransitionMixin<T> {
  _PageBasedMaterialPageRoute({
    @required MaterialPage<T> page,
  }) : assert(page != null),
       assert(opaque),
       super(settings: page);

  MaterialPage<T> get _page => settings as MaterialPage<T>;

  @override
  Widget buildContent(BuildContext context) {
    return _page.child;
  }

  @override
  bool get maintainState => _page.maintainState;

  @override
  bool get fullscreenDialog => _page.fullscreenDialog;

  @override
  String get debugLabel => '${super.debugLabel}(${_page.name})';
}