Question

我已经设法达到AnimatedList的位置，它将在新添加的项目中滑动。包裹我的列表项的Dismissible小部件控制着删除动画。我的问题是如何向SlideTransition添加某种动画曲线，以便可以控制新列表项在滑入时的显示方式。这是我到目前为止的工作：

@override
Widget build(BuildContext context) {
final checklists = Provider.of<Checklists>(context);

return AnimatedList(
  key: listKey,
  initialItemCount: checklists.lists.length,
  itemBuilder: (ctx, i, animation) {
    return SlideTransition(
      position: CurvedAnimation(parent: ).drive(child)  // <- this line needs changing
      child: _buildListItem(checklists.lists[i], i),          
    );
  },      
);
}

我不确定如何处理position参数。以前，对于标准SlideTransition，我只是使用

animation.drive(Tween(begin: Offset(0.2, 0), end: Offset(0.0, 0))),

可以正常工作，但是缺乏曲线缓和性。有什么想法吗？

修改为了清晰起见，这里是完整的.dart文件，以及我从父窗口小部件插入新项目的位置：

GlobalKey<AnimatedListState> recentListsAnimationKey = GlobalKey();

class RecentLists extends StatefulWidget {
  @override
  _RecentListsState createState() => _RecentListsState();
}

class _RecentListsState extends State<RecentLists>
    with TickerProviderStateMixin {
  Widget _buildListItem(Checklist list, int listIndex) {
    return Dismissible(
      key: ObjectKey(list.id),
      direction: DismissDirection.endToStart,
      background: Container(
        alignment: AlignmentDirectional.centerEnd,
        color: Theme.of(context).accentColor,
        child: Padding(
          padding: EdgeInsets.fromLTRB(0.0, 0.0, 10.0, 0.0),
          child: Icon(
            Icons.delete,
            color: Colors.white,
          ),
        ),
      ),
      child: ListTile(
        onTap: () {
          Navigator.push(
            context,
            MaterialPageRoute(
              builder: (ctx) => ListItemsScreen(list.id),
            ),
          );
        },
        title: Text(list.name),
        leading: Checkbox(
          value: list.completed,
          onChanged: (value) {
            setState(() {
              list.completed = value;
            });
          },
        ),
      ),
      onDismissed: (direction) {
        _onDeleteList(list, listIndex);
      },
    );
  }

  void _onDeleteList(Checklist list, int listIndex) {
    Provider.of<Checklists>(context).deleteList(list.id);
    recentListsAnimationKey.currentState
        .removeItem(listIndex, (_, __) => Container());

    Scaffold.of(context).showSnackBar(
      SnackBar(
        action: SnackBarAction(
          label: 'UNDO',
          onPressed: () {
            Provider.of<Checklists>(context).undoDeleteList(list, listIndex);
            recentListsAnimationKey.currentState
                .insertItem(listIndex, duration: Duration(milliseconds: 100));
          },
        ),
        content: Text(
          'List deleted',
          style: TextStyle(color: Theme.of(context).accentColor),
        ),
      ),
    );
  }

  AnimationController _controller;
  Animation<Offset> _position;

  @override
  void initState() {
    super.initState();
    _controller = AnimationController(
      duration: Duration(milliseconds: 200),
      vsync: this,
    );
    _position = Tween(
      begin: Offset(0.5, 0),
      end: Offset(0.0, 0),
    ).animate(
      CurvedAnimation(
        parent: _controller,
        curve: Curves.decelerate,
      ),
    );
    _controller.forward();
  }

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

  @override
  Widget build(BuildContext context) {
    final checklists = Provider.of<Checklists>(context);

    return AnimatedList(
      key: recentListsAnimationKey, 
      initialItemCount: checklists.lists.length,
      itemBuilder: (ctx, i, animation) {
        return SlideTransition(
          position: _position,
          child: _buildListItem(checklists.lists[i], i),
        );
      },
    );
  }
}

在这里，我将新项目插入列表。没有显示幻灯片动画。

void createNewList(BuildContext context) {
  if (nameController.text.isNotEmpty) {
    Provider.of<Checklists>(context).addList(nameController.text);
    recentListsAnimationKey.currentState.insertItem(0, duration: Duration(milliseconds: 100));
    nameController.clear();
   }
    Navigator.of(context).pop();
  }

Answer 1

在Flutter中，Animation只是一个类，它根据AnimationController提供的百分比从头到尾更改数据。您必须准备position的{{1}}的哪个实例。

Animation<Offset>

Answer 2

将Animation.drive函数与CurveTween链接到偏移补间。您的itemBuilder应该如下所示：

itemBuilder: (ctx, i, animation) {
    return SlideTransition(
      position: animation.drive(Tween(begin: Offset(2, 0.0), end: Offset(0.0, 0.0))
            .chain(CurveTween(curve: Curves.elasticInOut))),
      child: _buildListItem(checklists.lists[i], i),          
    );
  },

Flutter AnimatedList-向SlideTransition添加CurvedAnimation

2 个答案: