Question

StreamBuilder（

                    stream: firestore
                        .collection('users')
                        .document(user.uid)
                        .collection("notes")
                        .snapshots(),
                    builder: (context, snapshot) {
                      QuerySnapshot snap = snapshot?.data;
                      List<DocumentSnapshot> notes = snap?.documents;
                      return ListView.builder(
                        physics: AlwaysScrollableScrollPhysics(),
                        itemCount: notes?.length,
                        itemBuilder: (BuildContext context, int index) {
                          DocumentSnapshot doc = notes[index];
                          Map body = doc.data;
                          return Dismissible(
                            key: ObjectKey("${notes[index]}"),
                            background: stackBehindDismiss(),
                            direction: DismissDirection.endToStart,
                            onDismissed: (v) {
                              deleteNote(doc.documentID);
                            },
                            child: Padding(
                              padding: EdgeInsets.all(10),
                              child: InkWell(
                                onTap: () {
                                  Navigator.of(context).push(
                                    MaterialPageRoute(
                                      builder: (_) => DisplayScreen(
                                        title: body,
                                        docId: doc,
                                      ),
                                    ),
                                  );
                                },

                                child: _buildNotes(
                                    context,
                                    "${body["title"]}",
                                    "${body["content"]}"),
                              ),
                            ),
                          );
                        },
                      );
                    }),

这是我得到的错误

“以下NoSuchMethodError被抛出：方法'[]'在null上被调用。接收者：null 尝试致电：

引发异常时，这是堆栈：＃0 Object.noSuchMethod（dart：core-patch / object_patch.dart：51：5）

＃1 _HomeScreenState.build .. （软件包：firebase_note_app / screens / homescreen.dart：75：59）

＃2 SliverChildBuilderDelegate.build（package：flutter / src / widgets / sliver.dart：448：22）

＃3 SliverMultiBoxAdaptorElement._build。（软件包：flutter / src / widgets /sliver.dart:1136:67）

＃4 _HashMap.putIfAbsent（dart：collection-patch / collection_patch.dart：140：29） ...

”

StackTrace指向“ DocumentSnapshot doc = notes [index];”

Answer 1

看起来像是错别字，您可以使用ctrl + f来搜索该键[]

Answer 2

notes是null。您需要检查快照中是否有数据，并显示快照中是否有数据。

builder: (context, snapshot) {
                    if(snapshot.hasData) {//Check if there is data
                      QuerySnapshot snap = snapshot?.data;
                      List<DocumentSnapshot> notes = snap?.documents;
                      return ListView.builder(
                        physics: AlwaysScrollableScrollPhysics(),
                        itemCount: notes?.length,
                        itemBuilder: (BuildContext context, int index) {
                          DocumentSnapshot doc = notes[index];
                          Map body = doc.data;
                          return Dismissible(
                            key: ObjectKey("${notes[index]}"),
                            background: stackBehindDismiss(),
                            direction: DismissDirection.endToStart,
                            onDismissed: (v) {
                              deleteNote(doc.documentID);
                            },
                            child: Padding(
                              padding: EdgeInsets.all(10),
                              child: InkWell(
                                onTap: () {
                                  Navigator.of(context).push(
                                    MaterialPageRoute(
                                      builder: (_) => DisplayScreen(
                                        title: body,
                                        docId: doc,
                                      ),
                                    ),
                                  );
                                },
                       ...
                    }
                    else {//If there isn't data
                      //Return what you want to show before the stream emits its first event
                      return CircularProgressIndicator();
                    }

方法'[]'被调用为null

2 个答案: