在firebase中，我有一个名为selectedPlace的字段。在这个领域，餐厅，咖啡馆或居酒屋都可以进入。

我的代码中还有一个下拉按钮，包含了Restaurant、Cafe和Izakaya。我使用了一个streambuilder来显示posts集合中的所有文档，并使用.where（）来整理selectedPlace。代码如下：

class MatjipPage extends StatefulWidget {
      MatjipPage({super.key});
    
      @override
      State<MatjipPage> createState() => _MatjipPageState();
    }
    
    class _MatjipPageState extends State<MatjipPage> {
    
      @override
      Widget build(BuildContext context) {
        final width = MediaQuery.of(context).size.width;
        String? _selectedPlace;
        bool _filterActive = false;
    
        return Scaffold(
          body: CustomScrollView(
            slivers: <Widget>[
              SliverAppBar(
                collapsedHeight: 150,
                backgroundColor: Colors.white,
                floating: false,
                pinned: true,
                expandedHeight: 10,
                flexibleSpace: Container(
                  margin: EdgeInsets.only(top: 40),
                  child: Column(
                    children: [
                      Row(
                        mainAxisAlignment: MainAxisAlignment.spaceBetween,
                        children: [
                          IconButton(
                              onPressed: () {},
                              icon: Icon(
                                Icons.arrow_back_ios_new,
                                color: Colors.grey,
                              )),
                          IconButton(
                              onPressed: () {},
                              icon: Icon(
                                Icons.search,
                                color: Colors.black,
                                size: 35,
                                weight: 50,
                              ))
                        ],
                      ),
                      Row(
                        mainAxisAlignment: MainAxisAlignment.spaceAround,
                        children: [
                          Text(
                            'Restaurant Review',
                            style: TextStyle(
                                fontWeight: FontWeight.bold, fontSize: 18),
                          ),
                          IntrinsicHeight(
                            child: Row(
                              children: [
                                SizedBox(
                                  width: 83,
                                  child: DropdownBar(
                                    items: ['All', 'Restaurant', 'Cafe', 'Izakaya'],
                                    hintText: 'Sort By',
                                    onChanged: (newValue) {
                                      setState(() {
                                        if (newValue == 'All') {
                                          _filterActive = false;
                                        } else {
                                          _filterActive = true;
                                          _selectedPlace = newValue;
                                        }
                                        print('Selected Place: $_selectedPlace');
                                        print('Filter Active: $_filterActive');
                                      });
                                    },
                                  ),
                                )],
                            ),
                          )
                        ],
                      ),
                      SizedBox(
                        width: MediaQuery.of(context).size.width,
                        height: 3,
                        child: Container(
                          decoration: BoxDecoration(
                              gradient: LinearGradient(
                                  begin: Alignment.topLeft,
                                  end: Alignment.topRight,
                                  colors: [
                                Colors.white,
                                primaryColor,
                                Colors.white
                              ])),
                        ),
                      ),
                      Padding(
                        padding: EdgeInsets.only(top: 13, left: 20),
                        child: Row(
                          children: [
                            Padding(
                              padding: const EdgeInsets.only(right: 10),
                              child: SizedBox(
                                  width: 90,
                                  child: DropdownBarRound(
                                    items: ['Breakfast', 'Lunch', 'Dinner'],
                                    hintText: 'Time',
                                  )),
                            ),
                            SizedBox(
                                width: 95,
                                child: DropdownBarLoc(
                                  items: ['SHUBUYA', 'SHINJUKU', 'WASEDA'],
                                  hintText: 'Location',
                                )),
                            SizedBox(),
                          ],
                        ),
                      ),
                    ],
                  ),
                ),
              ),
              SliverList(
                delegate: SliverChildListDelegate([
                  StreamBuilder(
                    stream: FirebaseFirestore.instance
                        .collection('posts')
                        .where('selectedPlace', isEqualTo: _filterActive ? _selectedPlace : null)
                        .snapshots(),
                    builder: (context,
                        AsyncSnapshot<QuerySnapshot<Map<String, dynamic>>>
                            snapshot) {
                      if (snapshot.connectionState == ConnectionState.waiting) {
                        return const Center(
                          child: CircularProgressIndicator(),
                        );
                      }
                      return Container(
                        height: MediaQuery.of(context).size.height * 0.8,
                        child: ListView.builder(
                            itemCount: snapshot.data?.docs.length,
                            itemBuilder: (ctx, index) {
                              List<String> postUrls = snapshot.data?.docs[index]
                                  .get('postUrl')
                                  .split(',\n');
    
                              return Container(
                                padding: EdgeInsets.only(bottom: 25),
                                margin: EdgeInsets.symmetric(
                                  horizontal:
                                      width > webScreenSize ? width * 0.3 : 0,
                                  vertical: width > webScreenSize ? 15 : 0,
                                ),
                                child: PostCard(
                                  snap: snapshot.data?.docs[index].data(),
                                  postUrls: postUrls,
                                ),
                              );
                            }),
                      );
                    },
                  )
                ]),
              ),
            ],
          ),
          floatingActionButton: Padding(
            padding: const EdgeInsets.only(right: 16.0, bottom: 16.0),
            child: FloatingActionButton(
              onPressed: () {
                Navigator.push(context,
                    MaterialPageRoute(builder: (context) => AddPostScreen()));
              },
              child: Icon(Icons.add),
            ),
          ),
          floatingActionButtonLocation: FloatingActionButtonLocation.endFloat,
        );

_selectedPlace和_filterActive工作正常，因为我用print（）检查了它，但是帖子不会被整理出来，所有的文档都会显示在模拟器中。如果有人能帮我解决这个问题，我将不胜感激。非常感谢