Question

每当我尝试使用 .orderby("POST_ID", descending: true 时，我都会收到错误“NoSuchMethodError: The getter 'docs' was called on null.Receiver: null Tried Calling: docs”。如果有人对我为什么会收到此错误以及如何解决它有答案，请提供帮助！这是我的代码：

          Container(
          margin: EdgeInsets.only(top: 100.0),
          child: StreamBuilder(
              stream: FirebaseFirestore.instance
                  .collection("Cities")
                  .doc(globals.selectedCity)
                  .collection("Posts")
                  .orderBy("POST_ID", descending: true)
                  .where("Category", isEqualTo: globals.selectedCategory)
                  .snapshots(),
              builder: (context, postSnapshot) {
                return ListView.builder(
                  itemCount: postSnapshot.data.docs.length,
                  itemBuilder: (BuildContext context, int index) {
                    switch (postSnapshot.data.docs[index]["Type"]) {
                      case "Image":
                        return new ImageCard(
                          imageLink: postSnapshot.data.docs[index]
                              ["ImageLink"],
                          imageDescription: postSnapshot.data.docs[index]
                              ["ImageDescription"],
                          posterName: postSnapshot.data.docs[index]
                              ["PosterName"],
                        );
                        break;

                      case "Text":
                        return new TextCard(
                          postText: postSnapshot.data.docs[index]
                              ["PostText"],
                          posterName: postSnapshot.data.docs[index]
                              ["PosterName"],
                        );
                        break;

Answer 1

问题出在这里：

ID_t

您必须首先确保从 firestore 获取数据。在您的情况下，当连接状态正在连接或快照有错误时，您可以在空对象上调用 (postSnapshot.data.docs[index]["Type"])。考虑使用如下检查构建小部件树：

docs

“NoSuchMethodError：getter 'docs' 在 null 上被调用”错误 Flutter Firebase

1 个答案: