未定义的名称“Firestore”颤振

dependencies:
  flutter:
    sdk: flutter
    


  # The following adds the Cupertino Icons font to your application.
  # Use with the CupertinoIcons class for iOS style icons.
  cupertino_icons: ^1.0.2
  cloud_firestore:

我配置正确请帮忙

回答

var snapshot = FirebaseFirestore.instance
          .collection('chat')
          .orderBy('createdAt', descending: true)
          .snapshots();