颠倒Flutter中建立SliverFixedExtentList的顺序

Question

我的应用程序主页上有一个FutureBuilder，可以在将来完成后返回SliverFixedExtentList。看起来像这样：

class HomeScreen extends StatelessWidget {

  Future<QuerySnapshot> getQuerySnapshot(path){
    return Firestore.instance.collection(path).orderBy('date').getDocuments();
  }

  @override
  Widget build(BuildContext context) {
    final List<DocumentSnapshot> _documents = List<DocumentSnapshot>();
    var uid = Provider.of<UserState>(context).firebaseUser.uid;
    return FutureBuilder(
      future: getQuerySnapshot('eatenFoods/'+ uid +'/food'),
      builder: (BuildContext context, AsyncSnapshot<QuerySnapshot> snapshot){
        Widget child;
        if (snapshot.hasData){
          _documents.clear();
          snapshot.data.documents.forEach((doc)=> _documents.add(doc));
          child = SliverFixedExtentList(
            itemExtent: 150,
            delegate: new SliverChildBuilderDelegate(
              (context, index) => FoodItemCard(_documents[index]),
              childCount: _documents.length,
            ),
          );
        }else {
          child = SliverToBoxAdapter(child: CircularProgressIndicator());
        }
        return Scaffold(
          //some widgets
          body: CustomScrollView(
            slivers: <Widget> [
              SliverAppBar()
              child, //<-- here is the SliverFixedExtentList
            ]
          )

将来会从数据库中获取文档列表，然后依次将它们传递给帮助程序类，该帮助程序类会将数据包装在Card中。问题在于此实现将最新文档放在底部，而我希望它们位于顶部。我可以更改从数据库Firestore.instance.collection(path).orderBy('date', descending: true).getDocuments();中检索文档的顺序，但是由于每次返回页面时列表都不会完全重建，因此除非重新构建应用程序，否则不会显示新数据。我还尝试在自定义滚动视图中设置reverse: true，但这会反转所有内容，包括SliverAppBar。

是否有某种方法可以改变SliverFixedExtentList的构建方式，从而使较高的索引位于顶部？

Answer 1

而不是尝试反转SliverFixedExtentList，您可以反转项目...您要做的就是在for each loop之后反转_ documents。

请注意我添加的位置_ documents = _documents.reversed.toList（）

class HomeScreen extends StatelessWidget {

  Future<QuerySnapshot> getQuerySnapshot(path){
    return Firestore.instance.collection(path).orderBy('date').getDocuments();
  }

  @override
  Widget build(BuildContext context) {
    final List<DocumentSnapshot> _documents = List<DocumentSnapshot>();
    var uid = Provider.of<UserState>(context).firebaseUser.uid;
    return FutureBuilder(
      future: getQuerySnapshot('eatenFoods/'+ uid +'/food'),
      builder: (BuildContext context, AsyncSnapshot<QuerySnapshot> snapshot){
        Widget child;
        if (snapshot.hasData){
          _documents.clear();
          snapshot.data.documents.forEach((doc)=> _documents.add(doc));
          _documents = _documents.reversed.toList();
          child = SliverFixedExtentList(
            itemExtent: 150,
            delegate: new SliverChildBuilderDelegate(
              (context, index) => FoodItemCard(_documents[index]),
              childCount: _documents.length,
            ),
          );
        }else {
          child = SliverToBoxAdapter(child: CircularProgressIndicator());
        }
        return Scaffold(
          //some widgets
          body: CustomScrollView(
            slivers: <Widget> [
              SliverAppBar()
              child, //<-- here is the SliverFixedExtentList
            ]
          )