DART

flutter delete file

  Future<String> get _localPath async {
    final directory = await getApplicationDocumentsDirectory();

    return directory.path;
  }

  Future<File> get _localFile async {
    final path = await _localPath;
    print('path ${path}');
    return File('$path/counter.txt');
  }

  Future<int> deleteFile() async {
        try {
          final file = await _localFile;

          await file.delete();
        } catch (e) {
          return 0;
        }
      }

delete a document flutter

Firestore.instance.collection("chats").document("ROOM_1")  
    .collection("messages").document(snapshot.data.documents[index]["id"])
    .delete();