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the RadialExpansion widget, the core of the demo, builds the
widget tree that clips the image during the transition.
the clipped shape results from the intersection of a circular clip
(that grows during flight),
with a rectangular clip (that remains a constant size throughout).
to do this, it builds the following widget tree:
here’s the code:
key information:
the example defines the tweening interpolation using
MaterialRectCenterArcTween.
the default flight path for a hero animation
interpolates the tweens using the corners of the heroes.
this approach affects the hero’s aspect ratio during
the radial transformation, so the new flight path uses
MaterialRectCenterArcTween to interpolate the tweens using the
center point of each hero.
here’s the code:
the hero’s flight path still follows an arc,
but the image’s aspect ratio remains constant.
<topic_end>
<topic_start>
animate a page route transition
a design language, such as material, defines standard behaviors when
transitioning between routes (or screens). sometimes, though, a custom
transition between screens can make an app more unique. to help,
PageRouteBuilder provides an animation object.
this animation can be used with tween and
curve objects to customize the transition animation.
this recipe shows how to transition between
routes by animating the new route into view from
the bottom of the screen.
to create a custom page route transition, this recipe uses the following steps:
<topic_end>
<topic_start>
1. set up a PageRouteBuilder
to start, use a PageRouteBuilder to create a route.
PageRouteBuilder has two callbacks, one to build the content of the route
(pagebuilder), and one to build the route’s transition (transitionsbuilder).
info note
the child parameter in transitionsBuilder is the widget returned from
pageBuilder. the pageBuilder function is only called the first time the
route is built. the framework can avoid extra work because child stays the
same throughout the transition.
the following example creates two routes: a home route with a “go!” button, and
a second route titled “page 2”.
<code_start>
import 'package:flutter/material.dart';
void main() {
runApp(
const MaterialApp(
home: page1(),
),
);
}
class page1 extends StatelessWidget {
const page1({super.key});
@override
widget build(BuildContext context) {
return scaffold(
appBar: AppBar(),
body: center(
child: ElevatedButton(
onPressed: () {
Navigator.of(context).push(_createRoute());
},
child: const Text('Go!'),
),
),
);
}
}
route _createRoute() {
return PageRouteBuilder(
pageBuilder: (context, animation, secondaryAnimation) => const page2(),
transitionsBuilder: (context, animation, secondaryAnimation, child) {
return child;
},
);
}
class page2 extends StatelessWidget {
const page2({super.key});
@override
widget build(BuildContext context) {
return scaffold(
appBar: AppBar(),
body: const center(
child: Text('Page 2'),
),
);
}
}
<code_end>
<topic_end>
<topic_start>
2. create a tween
to make the new page animate in from the bottom, it should animate from
offset(0,1) to offset(0, 0) (usually defined using the offset.zero
constructor). in this case, the offset is a 2d vector for the
‘fractionaltranslation’ widget.
setting the dy argument to 1 represents a vertical translation one