没有为类型 'QuerySnapshot<Map<String, dynamic>>' 定义 getter 'documents'

Question

“for”循环中使用的类型“List>>”必须使用可分配给“Map”的类型参数实现“Iterable”。dart (for_in_of_invalid_element_type) 从此代码更改：

class CategoryServices {
String collection = "categories";
Firestore _firestore = Firestore.instance;

Future<List<CategoryModel>> getCategories() async =>
  _firestore.collection(collection).getDocuments().then((result) {
    List<CategoryModel> categories = [];
    for (DocumentSnapshot category in result.documents) {
      categories.add(CategoryModel.fromSnapshot(category));
    }
    return categories;
   });
   }

对此，但出现错误。我哪里做错了？

class CategoryModel {
 String? image;
  String? name;

 CategoryModel({this.image, this.name});

 // receiving data from server
 factory CategoryModel.fromMap(map) {
  return CategoryModel(image: map['image'], name: map['name']);
 }

 // sending data to our server
 Map<String, dynamic> toMap() {
  return {
  'image': image,
  'name': name,
   };
   }
   }

class CategoryServices {
String collection = "category";
FirebaseFirestore _firestore = FirebaseFirestore.instance;

 Future<List<CategoryModel>> getCategories() async =>
  _firestore.collection(collection).get().then((result) {
    List<CategoryModel> categories = [];
    for (Map category in result.docs) {  //error at this line
      categories.add(CategoryModel.fromMap(category));
    }
    return categories;
  });
  }

Answer 1

result.docs 的元素是QueryDocumentSnapshot，而不是Map。

我想你正在寻找：

for (QueryDocumentSnapshot category in result.docs) {
  categories.add(CategoryModel.fromMap(category.data()));
}
return categories;