My goal is to change the color and the opacity of the appbar when user scrolls down.
My logic is:
I came up with the following code:
import 'package:flutter/material.dart';
import 'package:gradient_app_bar/gradient_app_bar.dart';
void main() => runApp(MyApp());
class MyApp extends StatelessWidget {
@override
Widget build(BuildContext context) {
return MaterialApp(
title: 'Flutter Demo',
theme: ThemeData(
primarySwatch: Colors.blue,
),
home: MyHomePage(title: 'Flutter Demo Home Page'),
);
}
}
class MyHomePage extends StatefulWidget {
MyHomePage({Key key, this.title}) : super(key: key);
final String title;
@override
_MyHomePageState createState() => _MyHomePageState();
}
class _MyHomePageState extends State<MyHomePage> {
var _gradientColor1 = Colors.red[400];
var _gradientColor2 = Colors.red[800];
ScrollController _scrollViewController;
void changeColor(){
if((_scrollViewController.offset == 0) && (_gradientColor1 != Colors.red[400])){
setState(() {
_gradientColor1 = Colors.red[400];
_gradientColor2 = Colors.red[800];
});
}else if((_scrollViewController.offset <= 40) && (_gradientColor1 != Color.fromRGBO(66,165,245 ,0.4))){
setState(() {
_gradientColor1 = Color.fromRGBO(66,165,245 ,0.4);
_gradientColor2 = Color.fromRGBO(21,101,192 ,0.4);
});
}else if((_scrollViewController.offset <= 100) && (_scrollViewController.offset > 40)){
var opacity = _scrollViewController.offset/100;
setState(() {
_gradientColor1 = Color.fromRGBO(66,165,245 ,opacity);
_gradientColor2 = Color.fromRGBO(21,101,192 ,opacity);
});
}
}
@override
void initState() {
_scrollViewController = ScrollController(initialScrollOffset: 0.0);
_scrollViewController.addListener(changeColor);
}
@override
Widget build(BuildContext context) {
return Scaffold(
appBar: GradientAppBar(
backgroundColorStart: _gradientColor1,
backgroundColorEnd: _gradientColor2,
elevation: 0,
),
body: SingleChildScrollView(
controller: _scrollViewController,
child: Column(
children: <Widget>[
Container(color: Colors.red, height: 400,),
Container(color: Colors.purple, height: 400,),
],
),
),
);
}
}
It works as expected but it becomes laggy with a more complicated UI. In my example I'm using GradientAppbar: https://github.com/joostlek/GradientAppBar
i think the best approach Will be using AnimatedBuilder
and you will see that first container in body will not changed its color because widget state have not changed
and the result :
code:
import 'dart:math';
import 'package:flutter/material.dart';
class ProductDetails extends StatefulWidget {
@override
_ProductDetailsState createState() => _ProductDetailsState();
}
class _ProductDetailsState extends State<ProductDetails>
with TickerProviderStateMixin {
AnimationController _ColorAnimationController;
AnimationController _TextAnimationController;
Animation _colorTween, _iconColorTween;
Animation<Offset> _transTween;
@override
void initState() {
_ColorAnimationController =
AnimationController(vsync: this, duration: Duration(seconds: 0));
_colorTween = ColorTween(begin: Colors.transparent, end: Color(0xFFee4c4f))
.animate(_ColorAnimationController);
_iconColorTween = ColorTween(begin: Colors.grey, end: Colors.white)
.animate(_ColorAnimationController);
_TextAnimationController =
AnimationController(vsync: this, duration: Duration(seconds: 0));
_transTween = Tween(begin: Offset(-10, 40), end: Offset(-10, 0))
.animate(_TextAnimationController);
super.initState();
}
bool _scrollListener(ScrollNotification scrollInfo) {
if (scrollInfo.metrics.axis == Axis.vertical) {
_ColorAnimationController.animateTo(scrollInfo.metrics.pixels / 350);
_TextAnimationController.animateTo(
(scrollInfo.metrics.pixels - 350) / 50);
return true;
}
}
@override
Widget build(BuildContext context) {
return Scaffold(
backgroundColor: Color(0xFFEEEEEE),
body: NotificationListener<ScrollNotification>(
onNotification: _scrollListener,
child: Container(
height: double.infinity,
child: Stack(
children: <Widget>[
SingleChildScrollView(
child: Column(
children: <Widget>[
Container(
height: 150,
color:
Color((Random().nextDouble() * 0xFFFFFF).toInt() << 0)
.withOpacity(1),
width: 250,
),
Container(
height: 150,
color: Colors.pink,
width: 250,
),
Container(
height: 150,
color: Colors.deepOrange,
width: 250,
),
Container(
height: 150,
color: Colors.red,
width: 250,
),
Container(
height: 150,
color: Colors.white70,
width: 250,
),
],
),
),
Container(
height: 80,
child: AnimatedBuilder(
animation: _ColorAnimationController,
builder: (context, child) => AppBar(
backgroundColor: _colorTween.value,
elevation: 0,
titleSpacing: 0.0,
title: Transform.translate(
offset: _transTween.value,
child: Text(
"اسم کالا اینجا",
style: TextStyle(
color: Colors.white,
fontWeight: FontWeight.bold,
fontSize: 16),
),
),
iconTheme: IconThemeData(
color: _iconColorTween.value,
),
actions: <Widget>[
IconButton(
icon: Icon(
Icons.local_grocery_store,
),
onPressed: () {
// Navigator.of(context).push(TutorialOverlay());
},
),
IconButton(
icon: Icon(
Icons.more_vert,
),
onPressed: () {},
),
],
),
),
),
],
),
),
),
);
}
}