//動(dòng)畫(huà)控制器
AnimationController controller;
//AnimationController是一個(gè)特殊的Animation對(duì)象，在屏幕刷新的每一幀，就會(huì)生成一個(gè)新的值，
// 默認(rèn)情況下，AnimationController在給定的時(shí)間段內(nèi)會(huì)線性的生成從0.0到1.0的數(shù)字
//用來(lái)控制動(dòng)畫(huà)的開(kāi)始與結(jié)束以及設(shè)置動(dòng)畫(huà)的監(jiān)聽(tīng)
//vsync參數(shù)，存在vsync時(shí)會(huì)防止屏幕外動(dòng)畫(huà)（動(dòng)畫(huà)的UI不在當(dāng)前屏幕時(shí)）消耗不必要的資源
//duration 動(dòng)畫(huà)的時(shí)長(zhǎng)，這里設(shè)置的 seconds: 2 為2秒，當(dāng)然也可以設(shè)置毫秒 milliseconds：2000.
 controller =
 AnimationController(duration: const Duration(seconds: 2), vsync: this);
 //動(dòng)畫(huà)開(kāi)始、結(jié)束、向前移動(dòng)或向后移動(dòng)時(shí)會(huì)調(diào)用StatusListener
 controller.addStatusListener((status) {
 if (status == AnimationStatus.completed) {
 //動(dòng)畫(huà)從 controller.reverse() 反向執(zhí)行 結(jié)束時(shí)會(huì)回調(diào)此方法
 print("status is completed");
 // controller.reset(); 將動(dòng)畫(huà)重置到開(kāi)始前的狀態(tài)
 //開(kāi)始執(zhí)行
 //controller.forward();
 } else if (status == AnimationStatus.dismissed) {
 //動(dòng)畫(huà)從 controller.forward() 正向執(zhí)行 結(jié)束時(shí)會(huì)回調(diào)此方法
 print("status is dismissed");
 //controller.forward();
 }else if (status == AnimationStatus.forward) {
 print("status is forward");
 //執(zhí)行 controller.forward() 會(huì)回調(diào)此狀態(tài)
 }else if (status == AnimationStatus.reverse) {
 //執(zhí)行 controller.reverse() 會(huì)回調(diào)此狀態(tài)
 print("status is reverse");
 }
 });

//動(dòng)畫(huà)控制器
 AnimationController controller; 
 
 controller =
 AnimationController(duration: const Duration(seconds: 2), vsync: this);
 //動(dòng)畫(huà)開(kāi)始、結(jié)束、向前移動(dòng)或向后移動(dòng)時(shí)會(huì)調(diào)用StatusListener
 controller.addStatusListener((status) {
 if (status == AnimationStatus.completed) {
 //動(dòng)畫(huà)從 controller.forward() 正向執(zhí)行 結(jié)束時(shí)會(huì)回調(diào)此方法
 print("status is completed");
 //反向執(zhí)行
 //controller.reverse();
 } else if (status == AnimationStatus.dismissed) {
 //動(dòng)畫(huà)從 controller.reverse() 反向執(zhí)行 結(jié)束時(shí)會(huì)回調(diào)此方法
 print("status is dismissed");
 //controller.forward();
 } else if (status == AnimationStatus.forward) {
 print("status is forward");
 //執(zhí)行 controller.forward() 會(huì)回調(diào)此狀態(tài)
 } else if (status == AnimationStatus.reverse) {
 //執(zhí)行 controller.reverse() 會(huì)回調(diào)此狀態(tài)
 print("status is reverse");
 }
 });

 //漸變動(dòng)畫(huà)
 Widget buildSlideTransition() {
 return Center(
 child: FadeTransition(
 opacity: controller,
 //將要執(zhí)行動(dòng)畫(huà)的子view
 child: Container(
  width: 200,
  height: 200,
  color: Colors.grey,
  child: Image.network(
  "http://img5.duitang.com/uploads/item/201411/16/20141116124947_xBNxM.jpeg",
  ),
 ),
 ),
 );
 }

//動(dòng)畫(huà)開(kāi)始
controller.forward();

@override
 void dispose() {
 super.dispose();
 controller.dispose();
 }