在 Flutter 中将 Firestore DocumentSnapshot 转换为 Map

Question

我需要使用 Flutter 在 Firestore 中使用嵌套数组更新文档。

所以我需要将完整的文档放入一个 Map 中，重新排序“sections”数组中的映射，然后将数据存储回文档中。

然而，我不熟悉如何将快照 (DocumentSnapshot) 的数据放入地图。

下面是一个对我尝试实现的目标不起作用的示例：

final Map<String, dynamic> doc = snapshot.data as Map<String, dynamic>;

“snapshot.data”包含文档的值。文档的结构如下所示：

{
  name: "Course 1"
  sections: [
    {name: "Section 1"},
    {name: "Section 2"}
  ]
}

重新排序部分数组中的地图后，我需要将数据保存回文档中。

• 问题1：如何将snapshot.data 的内容读入Map？
• 问题 2：我会删除文档，然后重新添加吗？或者我可以更新所有内容吗？

这里功能齐全。相关代码在“onDragFinish”中。

 // Build editable list with draggable list tiles and swipe to delete
  List<Widget> buildListViewEdit() {
    final course = db.collection("school").document("3kRHuyk20UggHwm4wrUI")
      .collection("course").document("74UsE9x7Bsgnjz8zKozv").snapshots();

    return [
      StreamBuilder(
        stream: course,
        builder: (context, snapshot) {
          if (!snapshot.hasData) return const Text("Loading...");

          return Expanded(
            child: DragAndDropList(
              snapshot.data["sections"].length,
              itemBuilder: (context, index) {
                return Card(
                  child: ListTile(
                    title: Text(snapshot.data["sections"][index]["name"]),
                    onTap: () {
                      print("hello");
                    }                    
                  )
                );
              },
              onDragFinish: (before, after) {
                print('on drag finish $before $after');

                //final docString = snapshot.data.toString();

                final Map <String, dynamic> doc = snapshot.data;

                //final tempSections = List.castFrom(snapshot.data["sections"]).toList();

                //Map data = tempSections[before];

                //tempSections.removeAt(before);
                //tempSections.insert(after,data);

                //snapshot.data["sections"] = tempSections;

                //db.collection("school").document("3kRHuyk20UggHwm4wrUI")
                  //.collection("course").document("74UsE9x7Bsgnjz8zKozv").updateData(snapshot.data);

                //var line = snapshot.data["sections"][before];

                //snapshot.data["sections"].removeAt(before);
                //snapshot.data["sections"].insert(after,line);

                /*
                List<Map> sections = docCopy["sections"];

                Map data = docCopy["sections"][before];
                sections.removeAt(before);
                sections.insert(after, data);
                print(sections);   
                */         
              },
              canDrag: (index) {
                print('can drag $index');
                return index != 3;
              },
              canBeDraggedTo: (one, two) => true,
              dragElevation: 8.0,
            )
          );
        }
      )
    ];   
  }

尝试将 snapshot.data 复制到另一个变量时出错：

flutter: ??? EXCEPTION CAUGHT BY GESTURE LIBRARY ????????????????????????????????????????????????????????????
flutter: The following assertion was thrown while routing a pointer event:
flutter: type 'DocumentSnapshot' is not a subtype of type 'Map<String, dynamic>'
flutter:
flutter: Either the assertion indicates an error in the framework itself, or we should provide substantially
flutter: more information in this error message to help you determine and fix the underlying cause.
flutter: In either case, please report this assertion by filing a bug on GitHub:
flutter:   https://github.com/flutter/flutter/issues/new?template=BUG.md
flutter:
flutter: When the exception was thrown, this was the stack:
flutter: #0      _SectionScreenState.buildListViewEdit.<anonymous closure>.<anonymous closure> (package:teach_mob/screens/section_screen.dart:150:45)

工作示例

感谢大家的帮助。这是一个对我有用的完整示例：

  // Build editable list with draggable list tiles and swipe to delete
  List<Widget> buildListViewEdit() {
    final course = db.collection("school").document("3kRHuyk20UggHwm4wrUI")
      .collection("course").document("74UsE9x7Bsgnjz8zKozv").snapshots();

    return [
      StreamBuilder(
        stream: course,
        builder: (context, snapshot) {
          if (!snapshot.hasData) return const Text("Loading...");

          return Expanded(
            child: DragAndDropList(
              snapshot.data["sections"].length,
              itemBuilder: (context, index) {
                return Card(
                  child: ListTile(
                    title: Text(snapshot.data["sections"][index]["name"]),
                    onTap: () {
                      print("hello");
                    }                    
                  )
                );
              },
              onDragFinish: (before, after) {
                print('on drag finish $before $after');

                // Convert AsyncSnapshot to DocumentSnapshot and then
                // create a map that can be changed and updated.
                final Map <String, dynamic> doc = snapshot.data.data;

                // Convert fixed length list to dynamic list, because items in
                // fixed length lists can't be added / removed.
                final tempSections = List.castFrom(doc["sections"]).toList();

                // Get the data of the list item to be dragged
                // Remove the data from the current position
                // Add the data to the new position of the list
                Map data = tempSections[before];

                tempSections.removeAt(before);
                tempSections.insert(after,data);

                // Overwrite sections with new list array
                doc["sections"] = tempSections;

                // Store the data back into the firestore document
                db.collection("school")
                  .document("3kRHuyk20UggHwm4wrUI")
                  .collection("course")
                  .document("74UsE9x7Bsgnjz8zKozv")
                  .updateData(doc);
              },
              canDrag: (index) {
                print('can drag $index');
                return index != 3;
              },
              canBeDraggedTo: (one, two) => true,
              dragElevation: 8.0,
            )
          );
        }
      )
    ];   
  }

Answer 1

根据我们的讨论，快照不是DocumentSnapshot它是AsyncSnapshot

获取 DocumentSnaphot 使用 snapshot.data

获取您可以使用的实际地图 snapshot.data.data()

这将返回您正在寻找的 Map<String, dynamic> 。

Answer 2

看起来可能是因为您有一个流构建器，所以快照是一个AsyncSnapshot<dynamic>，当您获取其 .data 时，您会得到一个动态，它返回一个DocumentSnapshot，然后您需要在此对象上调用 .data以获得正确的.data Map<String, dynamic> data。

builder: (context, snapshot) {
final DocumentSnapshot  ds = snapshot.data;
final Map<String, dynamic> map = ds.data;
}

您还可以使用内置函数附加到数组，但看起来您想做一些疯狂的排序，所以一切都很好。

Answer 3

出于示例目的需要简化

class ItemsList extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    // get the course document using a stream
    Stream<DocumentSnapshot> courseDocStream = Firestore.instance
        .collection('Test')
        .document('4b1Pzw9MEGVxtnAO8g4w')
        .snapshots();

    return StreamBuilder<DocumentSnapshot>(
        stream: courseDocStream,
        builder: (context, AsyncSnapshot<DocumentSnapshot> snapshot) {
          if (snapshot.connectionState == ConnectionState.active) {

            // get course document
            var courseDocument = snapshot.data.data;

            // get sections from the document
            var sections = courseDocument['sections'];

            // build list using names from sections
            return ListView.builder(
              itemCount: sections != null ? sections.length : 0,
              itemBuilder: (_, int index) {
                print(sections[index]['name']);
                return ListTile(title: Text(sections[index]['name']));
              },
            );
          } else {
            return Container();
          }
        });
  }
}

结果

Answer 4

2020 年 9 月更新

To get data from a snapshot document you now have to call snapshot.data() (cloud_firestore 0.14.0 or higher)

Answer 5

2021 年 5 月更新

请参阅此处的迁移到 cloud_firestore 2.0.0 。

//Replace this:
- StreamBuilder<DocumentSnapshot>(
//With this:
+ StreamBuilder<DocumentSnapshot<Map<String, dynamic>>>(

创建变量时必须定义类型：

Future<void> example(
    -  DocumentReference documentReference,
    +  DocumentReference<Map<String, dynamic>> documentReference,
    -  CollectionReference collectionReference,
    +  CollectionReference<Map<String, dynamic>> collectionReference,
    -  Query query,
    +  Query<Map<String, dynamic>> query,
) {