flutter - 我如何获得下面给出的代码的类似计数？

Question

这是构成 Brew 并转到 BrewList 的 BrewTile。列表中的每个 brew 都有一个 like iconButton。我怎样才能让任何用户喜欢 Brew 或不喜欢 Brew..它不必显示喜欢 Brew 的用户的名字..它只需要显示喜欢的总数。如果第二次点击，用户还必须能够取消赞。

class Brew {
  final String id;
  final String name;
  final String sugars;
  final int strength;
  final int likeCount;

  Brew({this.id, this.name, this.sugars, this.strength, 
  this.likeCount});
  }


   class BrewData {
  final String id;
  final String name;
  final String sugars;
  final int strength;
  final int likeCount;

  BrewData({this.id, this.name, this.sugars, this.strength, 
  this.likeCount});


factory BrewData.fromDoc(DocumentSnapshot doc) {
    return BrewData(
      id: doc.documentID,
      name: doc['name'],
      sugars: doc['sugars'],
      strength: doc['strength'],
      likeCount: doc['likeCount'],
    );
  }

}






      class BrewTile extends StatefulWidget {
          final Brew brew;


          BrewTile({ this.brew});

          @override
          _BrewTileState createState() => _BrewTileState();
        }

        class _BrewTileState extends State<BrewTile> {
         int _likeCount = 0;
          bool _isLiked = false;

         @override
          Widget build(BuildContext context) {
            return Column(
              children: <Widget>[
              Padding(
              padding: const EdgeInsets.only(top: 8.0),
              child: Card(
                margin: EdgeInsets.fromLTRB(20.0, 6.0, 20.0, 0.0),
                child: ListTile(
                  leading: CircleAvatar(
                    radius: 25.0,
                    backgroundColor: Colors.brown[brew.strength],
                    backgroundImage: 
                    AssetImage('assets/coffee_icon.png'),
                  ),
                  title: Text(brew.name),
                  subtitle: Text('Takes ${brew.sugars} sugar(s)'),
                ),
              ),
            ),
                 Padding(
                  padding: EdgeInsets.symmetric(horizontal: 8.0),
                  child: Column(
                    crossAxisAlignment: CrossAxisAlignment.start,
                    children: <Widget>[
                      Row(
                        children: <Widget>[
                          IconButton(
                            icon: _isLiked
                                ? Icon(
                                    Icons.favorite,
                                    color: Colors.blue,
                                  )
                                : Icon(Icons.favorite_border),
                            iconSize: 30.0,
                            onPressed: () {
                              if (_isLiked) {
                          _likeCount++;
                          _isLiked = false;
                          print(_likeCount);
                          DatabaseService()
                              .updateLikes(id: widget.brew.id, value: 
       1);
                        } else {
                          print(true);
                          _likeCount--;
                          _isLiked = true;
                          DatabaseService()
                              .updateLikes(id: widget.brew.id, value: 
      -1);
                          print(_likeCount);
                        }
                      });
                            },
                          ),
                          Padding(
                            padding: EdgeInsets.symmetric(horizontal: 
                              12.0),
                            child: Text(
                              '${_likeCount.toString()} likes',
                              style: TextStyle(
                                fontSize: 16.0,
                                fontWeight: FontWeight.bold,
                              ),
                            ),
                          ),
                        ],
                      )
                    ],
                  ),
                )
              ],
            );
          }
        }



List<Brew> _brewListFromSnapshot(QuerySnapshot snapshot) {
    return snapshot.documents.map((doc) {
      //print(doc.data);
      return Brew(
          id: doc.documentID ?? '',
          name: doc.data['name'] ?? '',
          strength: doc.data['strength'] ?? 0,
          sugars: doc.data['sugars'] ?? '0',
          likeCount: doc.data['likeCount'] ?? 0,);
    }).toList();
  }


Future<void> updateLikesCount({String id int value}) async {
    return await brewCollection
        .document(id)
        .updateData({'likeCount': FieldValue.increment(value)});
  }

 Future<void> updateBrewData(String sugars, String name, int strength, int likeCount) async {
    return await brewCollection.document(uid).setData({
      'sugars': sugars,
      'name': name,
      'strength': strength,
      'likeCount': likeCount,
    });
  }


 Stream<BrewData> get brewData {
    return brewCollection.document(uid).snapshots().map(_brewDataFromSnapshot);
  }

它在控制台中给出了这个错误。

flutter: true
flutter: -1
[VERBOSE-2:ui_dart_state.cc(157)] Unhandled Exception: type 'MethodChannelFieldValue' is not a subtype of type 'FieldValuePlatform'
#0      FieldValue.increment 
package:cloud_firestore/src/field_value.dart:51
#1      DatabaseService.updateLikesCount 
package:myblogprofile/services/database.dart:75
#2      _BrewTileState.build.<anonymous closure>.<anonymous closure> 
package:myblogprofile/…/home/brew_tile.dart:77
#3      State.setState 
package:flutter/…/widgets/framework.dart:1148
#4      _BrewTileState.build.<anonymous closure> 
package:myblogprofile/…/home/brew_tile.dart:65
#5      _InkResponseState._handleTap 
package:flutter/…/material/ink_well.dart:706
#6      _InkResponseState.build.<anonymous closure> 
package:flutter/…/material/ink_well.dart:789
#7      GestureRecognizer.invokeCallback 
package:flutter/…/gestures/recognizer.dart:182
#8      TapGestureRecognizer.handleTapUp 
package:flutter/…/gestures/tap.dart:486
#9      BaseTapGestur<…>

Answer 1

请在 IconButton 的 onPressed 事件中添加以下代码...

setState(() {
      if (_isLiked) {
        _likeCount = _likeCount--;
         _isLiked = false;
      } else {
        _likeCount = _likeCount++;
         _isLiked = true;
      }
    });