Flutter動畫心動的感覺 Flutter動畫心動的感覺

Flutter動畫心動的感覺

爲了追求更好的用戶體驗，有時候我們需要一個類似心跳一樣跳動着的控件來吸引用戶的注意力，這是一個小小的優化需求，但是在 Flutter 裏動畫兩件套就像裹腳布一樣臭長，所以需要像封裝一個 AnimatedWidget，解放生產力。

實現動畫

混入 SingleTickerProviderStateMixin

當創建一個 AnimationController 時，需要傳遞一個vsync參數，存在vsync時會防止動畫的UI不在當前屏幕時消耗不必要的資源。 通過混入 SingleTickerProviderStateMixin 。

class _MyHomePageState extends State<MyHomePage>  with SingleTickerProviderStateMixin{}

創建動畫

創建一個間隔將近一秒鐘的動畫控制器：

  late final AnimationController animController;

  @override
  void initState() {
    super.initState();
    animController = AnimationController(
      duration: const Duration(milliseconds: 800),
      vsync: this,
    );
    }

心跳動畫是從小變大，再變小，所以需要一個值大小變化的動畫：

  late final Animation<double> animation;

  @override
  void initState() {
    super.initState();
    animController = AnimationController(
      duration: const Duration(milliseconds: 800),
      vsync: this,
    );
     animation = Tween<double>(
      begin: 0.9,
      end: 1.05,
    );
    }

心跳是不間斷的，所以需要監聽動畫完成時恢復動畫，再繼續開始動畫：

    animation = Tween<double>(
      begin: 0.9,
      end: 1.05,
    ).animate(animController)
      ..addListener(() {
        setState(() {});
      })
      ..addStatusListener((status) {
        if (status == AnimationStatus.completed) {
          animController.reverse();
        } else if (status == AnimationStatus.dismissed) {
          animController.forward();
        }
      });

使用縮放控件：

Transform.scale(
                scale: animation.value,
                child: const FlutterLogo(
                  size: 80,
                ),
              ),

爲了跳動效果，突出跳動動畫，把縮回去的時間改短：

   animController = AnimationController(
      reverseDuration: const Duration(milliseconds: 700),
      duration: const Duration(milliseconds: 800),
      vsync: this,
    );

最後別忘了釋放資源：

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

抽離成小組件

爲了每次用到類似的動畫只需引入即可，需要分離動畫和顯示的組件。新建一個BounceWidget，包含動畫，然後可以傳入UI組件：

class BounceWidget extends StatefulWidget {
  final Widget child;

  const BounceWidget({
    Key? key,
    required this.child,
  }) : super(key: key);

  @override
  State<BounceWidget> createState() => _BounceWidgetState();
}

繼續實現動畫：

class _BounceWidgetState extends State<BounceWidget>
    with SingleTickerProviderStateMixin {
  late Animation<double> animation;
  late AnimationController animController;

  @override
  void initState() {
    super.initState();
    animController = AnimationController(
      reverseDuration: const Duration(milliseconds: 700),
      duration: const Duration(milliseconds: 800),
      vsync: this,
    );
    animation = Tween<double>(
      begin: 0.9,
      end: 1.05,
    ).animate(animController)
      ..addListener(() {
        setState(() {});
      })
      ..addStatusListener((status) {
        if (status == AnimationStatus.completed) {
          animController.reverse();
        } else if (status == AnimationStatus.dismissed) {
          animController.forward();
        }
      });
    animController.forward();
  }

  @override
  Widget build(BuildContext context) {
    return Transform.scale(
      scale: animation.value,
      child: widget.child,
    );
  }

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

去引入動畫：

  Center(
              child: BounceWidget(
                child: FlutterLogo(
                  size: 80,
                ),
              ),

完整代碼：

void main() {
  runApp(const MyApp());
}

class MyApp extends StatelessWidget {
  const MyApp({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: const MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  const MyHomePage({Key? key, required this.title}) : super(key: key);

  final String title;

  @override
  State<MyHomePage> createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: Padding(
        padding: const EdgeInsets.only(top: 80, left: 16),
        child: Column(
          crossAxisAlignment: CrossAxisAlignment.start,
          children: const <Widget>[
            Text(
              "心動的",
              style: TextStyle(
                fontSize: 28,
                color: Colors.black,
              ),
            ),
            Text(
              "感覺",
              style: TextStyle(
                fontSize: 48,
                color: Colors.black,
              ),
            ),
            Center(
              child: BounceWidget(
                child: FlutterLogo(
                  size: 80,
                ),
              ),
            ),
          ],
        ),
      ),
    );
  }
}