Flutter：显示项目的总和

如何解决Flutter：显示项目的总和

所以我为我的电子商务应用制作了一个购物车页面，我想在脚手架底部显示商品的总和。 但问题是即使使用状态管理，它也没有给我预期的结果。

这是我的总价值控制器。

 class totalvaluecontroller extends GetxController {
  RxInt  total = 0.obs;}

这是为用户获取每个项目ID的代码

class appcart extends StatefulWidget {
  appcart({Key? key}) : super(key: key);

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

class _appcartState extends State<appcart> {
  @override
  Widget build(BuildContext context) {
    //bool all_items = false;
    totalvaluecontroller valuecontroller = Get.find();
    FirebaseController controller = Get.find();
    String custom_uid = controller.firebaseUser.value!.uid;
    return Scaffold(
          appBar: AppBar(
            centerTitle: true,title: Text(
              "Your Cart",),backgroundColor: Colors.black87,leading: IconButton(
                icon: Icon(Icons.arrow_back),onPressed: () {
                  Get.back();
                }),actions: [],body: Padding(
            padding: const EdgeInsets.symmetric(
                horizontal: 20.0,vertical: 20.0),child: StreamBuilder<DocumentSnapshot>(
              stream: FirebaseFirestore.instance
                  .collection("User_Carts")
                  .doc(custom_uid)
                  .snapshots(),builder: (BuildContext context,AsyncSnapshot<DocumentSnapshot>
                      snapshot) {
                if (snapshot.hasError) {
                  return Text("Error: ${snapshot.error}");
                }
                switch (snapshot.connectionState) {
                  case ConnectionState.waiting:
                    return SpinKitFadingCircle(
                        color: Colors.black45);
                  default:
                    return new ListView.builder(
                      itemCount:
                          snapshot.data!['Items'].length,itemBuilder: (BuildContext context,int index) {
                        return itemtile(
                          productid: snapshot.data!['Items']
                              [index],custom_uid: custom_uid,index: index,);
                      },);
                }
              },bottomNavigationBar:
              BottomAppBar(child: totaldisplaer()),//THE MAIN PROBLEM
        );
  }
}

这是获取有关每个产品的信息并显示在卡片中的代码

class itemtile extends StatelessWidget {
  final String productid;
  final String custom_uid;
  final int index;
  const itemtile(
      {required this.productid,required this.custom_uid,required this.index});

  @override
  Widget build(BuildContext context) {
    totalvaluecontroller valuecontroller = Get.find();
    return StreamBuilder<DocumentSnapshot>(
        stream: FirebaseFirestore.instance
            .collection("Products")
            .doc(productid.trim())
            .snapshots(),AsyncSnapshot<DocumentSnapshot> snapshot) {
          if (snapshot.hasError)
            return new Text('Error: ${snapshot.error}');
          /*else if (!snapshot.hasData) {
            return CircularProgressIndicator();
          }*/
          switch (snapshot.connectionState) {
            case ConnectionState.waiting:
              return SpinKitFadingCircle(
                  color: Colors.black45);
            default:
              valuecontroller.total =
                  valuecontroller.total +
                      (snapshot.data!["Price"] as int);
            
              return Card(
                elevation: 20.0,color: Color(snapshot.data!['Colour']),shape: RoundedRectangleBorder(
                    borderRadius:
                        BorderRadius.circular(15.0)),child: Padding(
                  padding: const EdgeInsets.all(8.0),child: Row(
                    children: <Widget>[
                      Container(
                        height: 50.0,width: 50.0,child: CachedNetworkImage(
                          placeholder: (context,url) =>
                              Center(
                                  child: SpinKitWave(
                            color: Colors.white38,)),imageUrl: snapshot.data!['Url'],SizedBox(
                        width: 10.0,Text(snapshot.data?['Brand']),Spacer(),Column(
                        children: <Widget>[
                          SizedBox(height: 25),Text(
                              "\$${snapshot.data?['Price']}"),],)
                    ],);
          }
        });
  }
}

现在因为我想在底部显示总和使用底部导航栏并使用此代码

class totaldisplaer extends StatelessWidget {
  const totaldisplaer({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    totalvaluecontroller valuecontroller = Get.find();

    return Obx(() => Text("${valuecontroller.total}"));
  }
}

给我以下错误

请提出解决方案