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full height of the page.
the transitionsBuilder callback has an animation parameter. it’s an
animation<double> that produces values between 0 and 1. convert the
animation into an animation using a tween:
<code_start>
transitionsBuilder: (context, animation, secondaryAnimation, child) {
const begin = offset(0.0, 1.0);
const end = offset.zero;
final tween = tween(begin: begin, end: end);
final offsetAnimation = animation.drive(tween);
return child;
},
<code_end>
<topic_end>
<topic_start>
3. use an AnimatedWidget
flutter has a set of widgets extending AnimatedWidget
that rebuild themselves when the value of the animation changes. for instance,
SlideTransition takes an Animation<Offset> and translates its child (using a
FractionalTranslation widget) whenever the value of the animation changes.
AnimatedWidget return a SlideTransition
with the Animation<Offset> and the child widget:
<code_start>
transitionsBuilder: (context, animation, secondaryAnimation, child) {
const begin = offset(0.0, 1.0);
const end = offset.zero;
final tween = tween(begin: begin, end: end);
final offsetAnimation = animation.drive(tween);
return SlideTransition(
position: offsetAnimation,
child: child,
);
},
<code_end>
<topic_end>
<topic_start>
4. use a CurveTween
flutter provides a selection of easing curves that
adjust the rate of the animation over time.
the curves class
provides a predefined set of commonly used curves.
for example, Curves.easeOut
makes the animation start quickly and end slowly.
to use a curve, create a new CurveTween
and pass it a curve:
<code_start>
var curve = curves.ease;
var curveTween = CurveTween(curve: curve);
<code_end>
this new tween still produces values from 0 to 1. in the next step, it will be
combined the Tween<Offset> from step 2.
<topic_end>
<topic_start>
5. combine the two tweens
to combine the tweens,
use chain():
<code_start>
const begin = offset(0.0, 1.0);
const end = offset.zero;
const curve = curves.ease;
var tween = tween(begin: begin, end: end).chain(CurveTween(curve: curve));
<code_end>
then use this tween by passing it to animation.drive(). this creates a new
Animation<Offset> that can be given to the SlideTransition widget:
<code_start>
return SlideTransition(
position: animation.drive(tween),
child: child,
);
<code_end>
this new tween (or animatable) produces offset values by first evaluating the
CurveTween, then evaluating the Tween<Offset>. when the animation runs, the
values are computed in this order:
another way to create an Animation<Offset> with an easing curve is to use a
CurvedAnimation:
<code_start>
transitionsBuilder: (context, animation, secondaryAnimation, child) {
const begin = offset(0.0, 1.0);
const end = offset.zero;
const curve = curves.ease;
final tween = tween(begin: begin, end: end);
final curvedAnimation = CurvedAnimation(
parent: animation,
curve: curve,
);
return SlideTransition(
position: tween.animate(curvedAnimation),
child: child,
);
}
<code_end>
<topic_end>
<topic_start>
interactive example
<code_start>
import 'package:flutter/material.dart';
void main() {
runApp(
const MaterialApp(
home: page1(),