flutter - Stream Builder 在 Flutter 中的先前数据之上更新数据

Question

我正在使用 StreamBuilder 从 firebase 实时数据库中获取数据(我经常更改它。)所以我希望我的 ListView 相应地更新 View 。但是它在做什么假设我有 3 个数据并且我又添加了一个然后显示所有 4 个数据低于前 3 个数据(即 7)直到我重新打开页面。

这是我的代码:

 Widget build(BuildContext context) {

  var ref =  FirebaseDatabase.instance.reference().child('Orders');
  List<PendingOrderLoader> pendingOrderLoaderList1 = [];

  
    return Scaffold(
      body: SafeArea(
          child: Column(
            children: <Widget>[

              Container(
                height: 200,
                child: StreamBuilder(
                  stream: FirebaseDatabase.instance.reference().child('Orders').onValue,
                    builder: (BuildContext context, snapshot){
                      if (snapshot.hasData && !snapshot.hasError && snapshot.data.snapshot.value!=null) {
                        DataSnapshot snapshot1 = snapshot.data.snapshot;

                        final key = snapshot1.value.keys;
                        for(var i in key)
                        {
                          print(i);
                          PendingOrderLoader pendingOrderLoader1 = new PendingOrderLoader(
                          
                            snapshot1.value[i]['OrderID'],
                            snapshot1.value[i]['Date'],
                            snapshot1.value[i]['Time'],
                           
                          );
                          pendingOrderLoaderList1.add(pendingOrderLoader1);
                        }
                        return snapshot.data.snapshot.value == null
                            ? SizedBox()

                            : ListView.builder(
                          scrollDirection: Axis.vertical,
                          itemCount: pendingOrderLoaderList1.length,
                          itemBuilder: (context, index) {
                            return Text("      "+
                                pendingOrderLoaderList1[index].OrderID
                            );
                          },
                        );
                      } else {
                        return   Center(child: CircularProgressIndicator());
                      }
                    }
                ),
              )


            ],
          )),

    );

  }

之前有 3 条数据，删除 1 条后，它正下方显示新数据。 我希望它只显示新数据。

Answer 1

定义这个列表

List pendingOrderLoaderList1 = [];

收到数据后在构建器内部

像这样:

Widget build(BuildContext context) { 
  var ref =  FirebaseDatabase.instance.reference().child('Orders');
    return Scaffold(
      body: SafeArea(
        child: Column(
         children: <Widget>[

           Container(
            height: 200,
             child: StreamBuilder(
              stream: FirebaseDatabase.instance.reference().child('Orders').onValue,
                builder: (BuildContext context, snapshot){
                  if (snapshot.hasData && !snapshot.hasError && snapshot.data.snapshot.value!=null) {
                    DataSnapshot snapshot1 = snapshot.data.snapshot;
                    List<PendingOrderLoader> pendingOrderLoaderList1 = [];
                    final key = snapshot1.value.keys;
                    for(var i in key)
                    {
                      print(i);
                      PendingOrderLoader pendingOrderLoader1 = new PendingOrderLoader(
                      
                        snapshot1.value[i]['OrderID'],
                        snapshot1.value[i]['Date'],
                        snapshot1.value[i]['Time'],
                       
                      );
                      pendingOrderLoaderList1.add(pendingOrderLoader1);
                    }
                    return snapshot.data.snapshot.value == null
                        ? SizedBox()

                        : ListView.builder(
                      scrollDirection: Axis.vertical,
                      itemCount: pendingOrderLoaderList1.length,
                      itemBuilder: (context, index) {
                        return Text("      "+
                            pendingOrderLoaderList1[index].OrderID
                        );
                      },
                    );
                  } else {
                    return   Center(child: CircularProgressIndicator());
                  }
                }
            ),
          )


        ],
      )),

);

  }