列表生成器在列表中添加或删除项目时重复数据的问题。

Question

我是新加入flutter的。当我添加新项目或从列表中删除项目时，列表生成器确实会更新列表，但问题是列表生成器也会显示以前的项目列表并显示新的更新项目列表。所以我想做的是保留新更新的项目列表而不是旧项目列表。

class AlarmPage extends StatefulWidget {
      final String title;
      AlarmPage({Key key, this.title}) : super(key: key);

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

    class _AlarmPageState extends State<AlarmPage> {
      String alarmName;
      // Test Function
      void _addAlarm() {
        setState(() {
          Navigator.push(
              context, MaterialPageRoute(builder: (context) => AddAlarm()));
        });
      }

      @override
      void initState() {
        super.initState();
        Provider.of<AlarmsProvider>(context, listen: false).getLocalStorage();
      }

      @override
      Widget build(BuildContext context) {
        List<Widget> allWidgetsAlarms = List<Widget>();

        return Consumer<AlarmsProvider>(builder: (context, alarmProviderItem, _) {
          List<String> localAlarms = alarmProviderItem.alarms;
          if (localAlarms != null) {
            localAlarms.forEach((item) {
              allWidgetsAlarms.add(
                Stack(
                  children: <Widget>[
                    InkWell(
                      child: Container(
                        color: Color(0xff212121),
                        padding: EdgeInsets.all(10),
                        child: Column(
                          children: <Widget>[
                            // Alarm Name & Title
                            Container(
                              decoration: BoxDecoration(
                                  border: Border(
                                bottom: BorderSide(width: 2),
                              )),
                              child: Row(
                                children: <Widget>[
                                  Icon(Icons.alarm, color: Colors.yellow),
                                  SizedBox(width: 20.0),
                                  Text('$item',
                                      style: TextStyle(
                                          color: Color(0xffC1C1C1),
                                          fontSize: 15.0,
                                          fontWeight: FontWeight.w900)),
                                  SizedBox(height: 5),
                                ],
                              ),
                            ),
                            SizedBox(height: 10),
                            // Alarm Time & Toggle Switch
                            Container(
                              child: Row(
                                children: <Widget>[
                                  Text(
                                    'Time',
                                    style: TextStyle(
                                        fontSize: 30, color: Colors.white),
                                  ),
                                  SizedBox(width: 20),
                                  Text(
                                    'AM / PM',
                                    style: TextStyle(
                                        fontSize: 20, color: Color(0xffB5B5B5)),
                                  ),
                                  SizedBox(width: 150),
                                  Icon(Icons.switch_camera, color: Colors.yellow),
                                ],
                              ),
                            ),
                            // Alarm Repeat
                            Container(
                              child: Row(children: <Widget>[
                                Text(
                                  'Repeat',
                                  style: TextStyle(
                                      fontSize: 11, color: Color(0xff616161)),
                                ),
                                Container(
                                  child: DaySelector(
                                    value: null,
                                    onChange: (value) {},
                                    color: Colors.yellow[400],
                                    mode: DaySelector.modeFull,
                                  ),
                                ),
                              ]),
                            ),
                          ],
                        ),
                      ),
                      onLongPress: () {
                        Navigator.push(
                            context,
                            MaterialPageRoute(
                                builder: (context) => AddAlarm(item: item)));
                      },
                    ),
                    SizedBox(height: 180),
                  ],
                ),
              );
              print(item);
            });
          }

          return Scaffold(
            appBar: AppBar(
              backgroundColor: Colors.black,
              title: Text('Azy Alarm'),
              centerTitle: true,
            ),
            body: Container(
              decoration: BoxDecoration(
                image: const DecorationImage(
                    fit: BoxFit.cover,
                    image: AssetImage('assets/images/background_image(dark).png')),
              ),
              // child: ListView(children: allWidgetsAlarms),

              child: ListView.builder(
                  itemCount: allWidgetsAlarms.length,
                  padding: const EdgeInsets.all(8.0),
                  itemBuilder: (BuildContext context, int index) {
                    return allWidgetsAlarms[index];
                  }),
            ),
            floatingActionButton: FloatingActionButton(
              child: Icon(Icons.add),
              backgroundColor: Colors.blue,
              elevation: 0,
              onPressed: _addAlarm,
            ),
          );
        });
      }
    }

Answer 1

所以我认为你的问题是这一行。allWidgetsAlarms.add( 你构建了 allWidgetsAlarms 在你的构建器中，但构建器不会在每次你的 Consumer 重建，因此它只是将新的内容追加到列表的最后。为了解决这个问题，请保持原来初始化的 allWidgetsAlarms 的顶部，添加以下一行。

allWidgetsAlarms = List<Widget>();

这将会重新调用 allWidgetsAlarms. 希望能帮到你