将数据添加到本地存储中

Question

我使用https://pub.dev/packages/localstorage在Flutter应用中创建本地存储。我在“事件”小部件中创建了一些用于此本地存储的方法

class Event extends StatefulWidget {
  final eventInfo;
  Event({Key key, List eventInfo})
      : this.eventInfo = eventInfo,
        super(key: key);

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

class FavName {
  String eventName;
  FavName({this.eventName});

  get favEventName {
    return eventName;
  }

  toJSONEncodable() {
    Map<String, dynamic> m = new Map();

    m['Name'] = eventName;

    return m;
  }
}

class FavList {
  List<FavName> favNameList;

  FavList() {
    favNameList = new List();
  }

  toJSONEncodable() {
    return favNameList.map((item) {
      return item.toJSONEncodable();
    }).toList();
  }
}

class _EventState extends State<Event> {

  final FavList list = new FavList();
  final LocalStorage storage = new LocalStorage('favList');

  addItem(String eventName) {
    setState(() {
      final item = new FavName(eventName: eventName);
      list.favNameList.add(item);
      _saveToStorage();
    });
  }

  deleteItem(String eventName) {
    setState(() {
      final item = new FavName(eventName: eventName);
      list.favNameList.remove(item);
      _saveToStorage();
    });
  }

  _saveToStorage() {
    storage.setItem('favList', list.toJSONEncodable());
  }

 . . .

所以我想通过按钮将字符串添加到本地存储中。这是我的按钮代码。

child: IconButton(
                icon: Icon(
                  Icons.star,
                  color: _iconColors,
                ),
                onPressed: () {
                  print(name);
                  (storage.getItem(name)) ? deleteItem(name)
                  : addItem(name);
                  setState(() {
                    if (storage.getItem(name) == null) {
                      _iconColors = Colors.grey;
                    } else {
                      _iconColors = Colors.yellow;
                    }
                  });
                })

但是当我点击按钮时，出现此错误

I/flutter (27489): 2-Art Event          //Print the string that I want to add to the local storage

════════ Exception caught by gesture ═══════════════════════════════════════════
The following assertion was thrown while handling a gesture:
Failed assertion: boolean expression must not be null

When the exception was thrown, this was the stack
#0      _EventState.buildInfo.<anonymous closure> 
package:lx_building/screens/event.dart:190
#1      _InkResponseState._handleTap 
package:flutter/…/material/ink_well.dart:772
#2      _InkResponseState.build.<anonymous closure> 
package:flutter/…/material/ink_well.dart:855
#3      GestureRecognizer.invokeCallback 
package:flutter/…/gestures/recognizer.dart:182
#4      TapGestureRecognizer.handleTapUp 
package:flutter/…/gestures/tap.dart:522
...
Handler: "onTap"
Recognizer: TapGestureRecognizer#1f697
    debugOwner: GestureDetector
    state: possible
    won arena
    finalPosition: Offset(324.7, 264.3)
    finalLocalPosition: Offset(32.4, 9.7)
    button: 1
    sent tap down
════════════════════════════════════════════════════════════════════════════════

我该如何解决？

Answer 1

[storage.getItem(name)返回存储的数据，通常是Map。

在您的情况下，您必须使用布尔值。您可以测试返回的内容不为null：

(storage.getItem(name) != null) ? deleteItem(name)
                  : addItem(name);