class OpacityBanner extends StatefulWidget {
 @override
 _OpacityBannerState createState() => _OpacityBannerState();
}

class _OpacityBannerState extends State<OpacityBanner> {
 int zIndex = 0;
 List<String> list = ['ff0000', '00ff00', '0000ff', 'ffff00'];
 Timer timer;

 //setInterval控制當(dāng)前動(dòng)畫元素的下標(biāo)，實(shí)現(xiàn)動(dòng)畫輪播
 autoPlay() {
 var second = const Duration(seconds: 2);
 timer = Timer.periodic(second, (t) {
  setState(() {
  zIndex = (++zIndex) % list.length;
  });
 });
 }

 @override
 void initState() {
 super.initState();
 timer = Timer(Duration(seconds: 2), autoPlay);
 }

 @override
 void dispose() {
 if (timer != null) timer.cancel();
 super.dispose();
 }

 @override
 Widget build(BuildContext context) {
 return Scaffold(
 body: Stack(alignment: Alignment.center, children: [
  Stack(
   children: list
    .asMap()
    .keys
    .map<Widget>((i) => AnimatedOpacity(
     curve: Curves.easeIn,
     duration: Duration(milliseconds: 600),
     opacity: i == zIndex ? 1 : 0,
     child: Container(
      color: Color(int.parse(list[i], radix: 16)).withAlpha(255),
      height: 300, //100%
     ),
     ))
    .toList()),
  Positioned(
   bottom: 20,
   child: Row(
    children: list
     .asMap()
     .keys
     .map((i) => Container(
      width: 10,
      height: 10,
      margin: EdgeInsets.symmetric(horizontal: 5),
      decoration:
       BoxDecoration(color: i == zIndex ? Colors.blue : Colors.grey, shape: BoxShape.circle)))
     .toList()))
 ]));
 }
}

class SlideBanner extends StatefulWidget {
 @override
 _SlideBannerState createState() => _SlideBannerState();
}

class _SlideBannerState extends State<SlideBanner> {
 List<String> list = [
 'https://upload-images.jianshu.io/upload_images/127924-dec37275411437de.jpg',
 '//upload-images.jianshu.io/upload_images/127924-0999617a887bb6a3.jpg',
 '//upload-images.jianshu.io/upload_images/127924-b48e22b6aef713ae.jpg',
 '//upload-images.jianshu.io/upload_images/127924-b06e44e6a17caf43.jpg'
 ];
 double dx = 0;//距離
 int curr = 0;//要移出的下標(biāo)
 int next = 0;//要移入的下標(biāo)
 bool toLeft = true;//自動(dòng)播放的方向，默認(rèn)向左
 Timer timer;

 /** 輪播圖滑動(dòng)相關(guān) **/
 dragStart(Offset offset) {
 dx = 0;
 }

 //累計(jì)位移距離
 dragUpdate(Offset offset) {
 var x = offset.dx;
 dx += x;
 }
	
 //達(dá)到一定距離后則觸發(fā)輪播圖左右滑動(dòng)
 dragEnd(Velocity v) {
 if (dx.abs() < 20) return;
 timer.cancel();
 if (dx < 0) {
  //向左
  if (!toLeft) {
  setState(() {
   toLeft = true;
   curr = next - 1 < 0 ? list.length - 1 : next - 1;
  });
  }
  setState(() {
  curr = next;
  next = (++next) % list.length;
  });
 } else {
  //向右
  if (toLeft) {
  setState(() {
   toLeft = false;
   curr = (next + 1) % list.length;
  });
  }
  setState(() {
  curr = next;
  next = --next < 0 ? list.length - 1 : next;
  });
 }
 //setTimeout
 timer = Timer(Duration(seconds: 2), autoPlay);
 }

 autoPlay() {
 var second = const Duration(seconds: 2);
 timer = Timer.periodic(second, (t) {
  setState(() {
  toLeft = true;
  curr = next;
  next = (++next) % list.length;
  });
 });
 }

 @override
 void initState() {
 super.initState();
 timer = Timer(Duration(seconds: 2), autoPlay);
 }

 @override
 void dispose() {
 if (timer != null) timer.cancel();
 super.dispose();
 }

 @override
 Widget build(BuildContext context) {
 final size = MediaQuery.of(context).size;
 final width = size.width;
 return Scaffold(
  body: GestureDetector(
   onHorizontalDragStart: (details) => dragStart(details.globalPosition),
   onHorizontalDragUpdate: (details) => dragUpdate(details.delta),
   onHorizontalDragEnd: (details) => dragEnd(details.velocity),
   child: Stack(
    children: list
     .asMap()
     .keys
     .map((i) => AnimatedContainer(
      duration: Duration(milliseconds: (i == next || i == curr) ? 600 : 0),
      curve: Curves.easeIn,
      transform: Matrix4.translationValues(
       i == next ? 0 : i == curr ? (toLeft ? -width : width) : (toLeft ? width : -width), 0, 0),
      width: width,
      height: 300,
      child: Image.network(list[i], width: width, height:double.infinity ,fit: BoxFit.cover)))
     .toList())));
 }
}