如何以流畅的动画从页面视图中删除页面？

Question

我对颤振动画还是新手，我正在尝试制作一个 PageView，当您用动画按下它时它会被关闭。

我有这个代码：

class Carroussel extends StatefulWidget {
  @override
  _CarrousselState createState() => new _CarrousselState();
}

class _CarrousselState extends State<Carroussel> {
  PageController controller;
  int currentpage = 0;

  @override
  initState() {
    super.initState();
    controller = new PageController(
      initialPage: currentpage,
      keepPage: false,
      viewportFraction: 0.5,
    );
  }

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

  @override
  Widget build(BuildContext context) {
    return new Scaffold(
      body: new Center(
        child: new Container(
          child: new PageView.builder(
              onPageChanged: (value) {
                setState(() {
                  currentpage = value;
                });
              },
              controller: controller,
              itemBuilder: (context, index) => builder(index)),
        ),
      ),
    );
  }

  builder(int index) {
    return new AnimatedBuilder(
      animation: controller,
      builder: (context, child) {
        double value = 1.0;
        if (pageController.position.haveDimensions) {
          value = controller.page - index;
          value = (1 - (value.abs() * .5)).clamp(0.0, 1.0);
        }

        return new Center(
          child: new SizedBox(
            height: Curves.easeOut.transform(value) * 300,
            width: Curves.easeOut.transform(value) * 250,
            child: child,
          ),
        );
      },
      child: new Container(
        margin: const EdgeInsets.all(8.0),
        color: index % 2 == 0 ? Colors.blue : Colors.red,
      ),
    );
  }
}

上述代码的作者：https ://stackoverflow.com/a/47357960/1194779

这会产生以下结果：

现在，我需要在按下卡片后以动画方式将其关闭。

我尝试实现将卡片向下滑动的 SlideTransition。但我无法使 PageView 为刚刚删除的卡片的填充空白空间设置动画。

Answer 1

您可以使用Dismissible在小部件上启用滑动手势。不过，当与 PageView 一起使用时，Dismissible 会产生可能不受欢迎的卡顿。

class Carousel extends StatefulWidget {
  @override
  _CarouselState createState() => _CarouselState();
}

class _CarouselState extends State<Carousel>{
  late PageController controller;
  int currentPage = 0;
  List<String> listItem = ['Page 1', 'Page 2', 'Page 3', 'Page 4'];

  @override
  initState() {
    super.initState();
    controller = PageController(
      initialPage: currentPage,
      keepPage: false,
      viewportFraction: 0.5,
    );
  }

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

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Center(
        child: Container(
          child: PageView.builder(
            itemCount: listItem.length,
            onPageChanged: (value) {
              setState(() {
                currentPage = value;
              });
            },
            controller: controller,
            itemBuilder: (BuildContext context, int index) =>
                pageBuilder(index),
          ),
        ),
      ),
    );
  }

  pageBuilder(int index) {
    var dismissibleKey = GlobalKey<State>();
    return AnimatedBuilder(
      animation: controller,
      builder: (context, child) {
        double value = 1.0;
        if (controller.position.haveDimensions) {
          value = controller.page! - index;
          value = (1 - (value.abs() * .5)).clamp(0.0, 1.0);
        }

        return Center(
          child: SizedBox(
            height: Curves.easeOut.transform(value) * 300,
            width: Curves.easeOut.transform(value) * 250,
            child: child,
          ),
        );
      },
      child: Dismissible(
        key: dismissibleKey,
        direction: DismissDirection.down,
        onDismissed: (DismissDirection direction) {
          /// Remove item from List
          setState(() {
            listItem.removeAt(index);
          });
        },
        child: InkWell(
          onLongPress: () {
            debugPrint('Delete! $index');
            setState(() {
              listItem.removeAt(index);
            });
          },
          onTap: () {
            controller.animateToPage(index,
                duration: Duration(milliseconds: 500), curve: Curves.ease);
          },
          child: Container(
            margin: const EdgeInsets.all(8.0),
            // color: index % 2 == 0 ? Colors.blue : Colors.red,
            color: Colors.lightBlueAccent,
            child: Center(
              child: Text('${listItem[index]}'),
            ),
          ),
        ),
      ),
    );
  }
}