使用SliverAppBar在Flutter中设计这个动画

Question

使用SliverAppBar在Flutter中设计这个动画

flutterdartflutter-layoutflutter-animationflutter-sliver

7

这是我想要制作的效果，但我无法实现它，以下是我的代码:

@override
  Widget build(BuildContext context) {
    return Scaffold(
      body: NestedScrollView(
        headerSliverBuilder: (BuildContext context, bool innerBoxIsScrolled){
          return [
            SliverAppBar(
              expandedHeight: 120,
              floating: false,
              pinned: false,
              flexibleSpace: Container(
                padding: EdgeInsets.all(10),
                height: 160,
                width: double.infinity,
                child: Column(
                  mainAxisAlignment: MainAxisAlignment.end,
                  crossAxisAlignment: CrossAxisAlignment.start,
                  children: <Widget>[
                    Align(
                        alignment: Alignment.topCenter,
                        child: Text(
                          'Hello World',
                        )),
                    Padding(
                      padding: EdgeInsets.only(top: 16),
                      child: Image.asset(
                        'assets/images/banner.png',
                      ),
                    ),
                  ],
                ),
              ),
            ),
          ];
        },
        body: ListView.builder(),
      ),
    );
  }

我尝试了使用flexible和expanded的SliverAppBar，但未能实现。

更新 - 列表的第一个元素正在文本字段后面。我希望只有在动画完成时才滚动。

- pratikkarad

1

个人认为仅通过SliversAppBar是不可能实现的。你需要创建自己的自定义应用程序栏，然后使用Hero Animation（将文本从左侧移动到中心），AnimatedContainer（缩小容器高度），AnimationController，FadeTransition，并监听您的Listview控制器。这有点复杂。 - fadhli-sulaimi

让我试一下，实施后会回复您。谢谢@FadhliS - pratikkarad

我会尝试使用我提到的所有小部件为您提供解决方案。对于我来说，实现您想要的效果也不容易。您可以阅读我找到的这篇博客文章，了解动画的工作原理，并希望能够帮助您。https://www.smashingmagazine.com/2019/10/animation-apps-flutter/ - fadhli-sulaimi

1个回答

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原文链接

- Nardeepsinh Vaghela · Accepted Answer

更新的答案，

   @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: CustomScrollView(
        slivers: <Widget>[
          TransitionAppBar(
            extent: 250,
            avatar: Text("Rancho"),
            title: Container(
              margin: EdgeInsets.symmetric(horizontal: 20.0, vertical: 0),
              decoration: BoxDecoration(
                  color: Colors.grey[200],
                  borderRadius: BorderRadius.all(Radius.circular(5.0))),
              child: Row(children: <Widget>[
                Padding(
                  padding: EdgeInsets.only(left: 20.0, right: 10.0),
                  child: Icon(Icons.search),
                ),
                Expanded(
                  child: TextFormField(
                    keyboardType: TextInputType.text,
                    textInputAction: TextInputAction.done,
                    cursorColor: Colors.black,
                    autofocus: false,
                    style: TextField_Style,
                    decoration: InputDecoration(
                        filled: true,
                        fillColor: Colors.transparent,
                        contentPadding:
                            EdgeInsets.symmetric(vertical: 10, horizontal: 15),
                        hintText: "Search",
                        border: InputBorder.none,
                        disabledBorder: OutlineInputBorder(
                          borderSide: new BorderSide(color: Colors.transparent),
                          borderRadius: new BorderRadius.circular(2),
                        ),
                        focusedBorder: OutlineInputBorder(
                          borderSide: new BorderSide(color: Colors.transparent),
                          borderRadius: new BorderRadius.circular(2),
                        )),
                  ),
                )
              ]),
            ),
          ),
          SliverList(
              delegate: SliverChildBuilderDelegate((context, index) {
            return Container(
                color: Colors.blue,
                child: ListTile(
                  title: Text("${index}a"),
                ));
          }, childCount: 25))
        ],
      ),
    );
  }

.

class TransitionAppBar extends StatelessWidget {
  final Widget avatar;
  final Widget title;
  final double extent;

  TransitionAppBar({this.avatar, this.title, this.extent = 250, Key key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return SliverPersistentHeader(
      pinned: true,
      delegate: _TransitionAppBarDelegate(
        avatar: avatar,
        title: title,
        extent: extent > 200 ? extent : 200
      ),
    );
  }
}

class _TransitionAppBarDelegate extends SliverPersistentHeaderDelegate {
  final _avatarMarginTween = EdgeInsetsTween(
      begin: EdgeInsets.only(bottom: 70, left: 30),
      end: EdgeInsets.only(left: 0.0, top: 30.0));
  final _avatarAlignTween =
      AlignmentTween(begin: Alignment.bottomLeft, end: Alignment.topCenter);

  final Widget avatar;
  final Widget title;
  final double extent;

  _TransitionAppBarDelegate({this.avatar, this.title, this.extent = 250})
      : assert(avatar != null),
        assert(extent == null || extent >= 200),
        assert(title != null);

  @override
  Widget build(
      BuildContext context, double shrinkOffset, bool overlapsContent) {
    double tempVal = 34 * maxExtent / 100;
    final progress =  shrinkOffset > tempVal ? 1.0 : shrinkOffset / tempVal;
    print("Objechjkf === ${progress} ${shrinkOffset}");
    final avatarMargin = _avatarMarginTween.lerp(progress);
    final avatarAlign = _avatarAlignTween.lerp(progress);

    return Stack(
      children: <Widget>[
        AnimatedContainer(
          duration: Duration(milliseconds: 100),
          height: shrinkOffset * 2,
          constraints: BoxConstraints(maxHeight: minExtent),
          color: Colors.redAccent,
        ),
        Padding(
          padding: avatarMargin,
          child: Align(
            alignment: avatarAlign,
              child: avatar
          ),
        ),
        Padding(
          padding: EdgeInsets.only(bottom: 10),
          child: Align(
            alignment: Alignment.bottomCenter,
            child: title,
          ),
        )
      ],
    );
  }

  @override
  double get maxExtent => extent;

  @override
  double get minExtent => (maxExtent * 68) / 100;

  @override
  bool shouldRebuild(_TransitionAppBarDelegate oldDelegate) {
    return avatar != oldDelegate.avatar || title != oldDelegate.title;
  }
}