Question

我试图根据用户单击的屏幕来更改我的应用栏的高度。我以前使用过setState，但由于屏幕上有很多组件，所以更喜欢用streambuilder来做。我遇到的问题是使用streambuilder时出现错误

这是我的代码

 Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: StreamBuilder<Object>(
            stream: bloc.titleStream,
            initialData: home,
            builder: (context, snapshot) {
              return Text(snapshot.data);
            }
        ),
        backgroundColor: colorPrimary,
        elevation: StreamBuilder<double>(
            stream: bloc.appBarElevetionStream,
           // initialData: 0.0,
            builder: (context, snapshot) {
              return snapshot.data.toDouble();
            }
        ),
        actions: <Widget>[
          Builder(
              builder: (context) => bloc.navigationProvider.currentNavigation == home ?
                   homeCalendar(context):otherCalendar(context) //if it's not 0 we return an empty widget
          )
        ],
      ),
      drawer: DrawerNavigation(),
      body: homeScreen()
);

这是集团的代码

import 'dart:async';
import 'dart:ui';

import 'package:finsec/features/common/presentation/bloc/navigation_provider.dart';

class NavigationDrawerBloc {
  final navigationController = StreamController();
  StreamController<String> _title = StreamController<String>();
  StreamController<String> _drawerItemColor = StreamController<String>();
  StreamController<double> _appBarElevetion = StreamController<double>();

  NavigationProvider navigationProvider = new NavigationProvider();

  Stream get getNavigation => navigationController.stream;
  Stream<String> get titleStream => _title.stream;
  Stream<String> get itemColorStream => _drawerItemColor.stream;
  Stream<double> get appBarElevetionStream => _appBarElevetion.stream;


  // Color color = Color(0xffECECEC);

  void updateNavigation(String navigation, String title, double elevation) {
    navigationProvider.updateNavigation(navigation, title, elevation);
    navigationController.sink.add(navigationProvider.currentNavigation);
    _title.sink.add(title);
    _drawerItemColor.sink.add('gray');
    _appBarElevetion.sink.add(elevation);

  }

  void dispose() {
    navigationController.close();
    _title.close();
  }
}

final bloc = NavigationDrawerBloc();

我的提供者类

import 'package:finsec/core/res/export_resources.dart';

class NavigationProvider {
  String currentNavigation = home;
  String currentTitle = home;
  String drawerItemColor = 'gray';
  double appBarElevation = 0.0;

  void updateNavigation(String navigation, String title, double elevation) {
    currentNavigation = navigation;
    currentTitle = title;
    drawerItemColor = 'gray';
    appBarElevation = elevation;
  }
}

在构建功能中，appbar的海拔高度属性出现错误

  elevation: StreamBuilder<double>(
            stream: bloc.appBarElevetionStream,
           // initialData: 0.0,
            builder: (context, snapshot) {
              return snapshot.data.toDouble();
            }
        ),

错误是：无法将参数类型StreamBuilder分配给double类型的参数。返回类型'double'并不是闭包上下文所要求的'widget'

有什么方法可以将streambuilder输出转换为double以便可以在appbar的height属性中使用它？如何在海拔属性中使用streambuilder？预先感谢

Answer 1

StreamBuilder返回一个widget。 double中的StreamBuilder是stream而非StreamBuilder返回的数据类型。

如注释中所指定，将Scaffold包裹在Stream Bulder中，或使用您以前使用setState的方法。

Answer 2

StreamBuilder不仅返回一个值，它还是带有构建器的窗口小部件本身，该构建器在流可用时提供流的值。将StreamBuilder包裹在Scaffold周围，并以相同的方式访问值。

Widget build(BuildContext context) {
  return StreamBuilder<double>(
    stream: bloc.appBarElevetionStream,
    initialData: 0.0,
    builder: (context, snapshot) {
      return Scaffold(
        appBar: AppBar(
          title: StreamBuilder<Object>(
              stream: bloc.titleStream,
              initialData: home,
              builder: (context, snapshot) {
                return Text(snapshot.data);
              }
          ),
          backgroundColor: colorPrimary,
          elevation: snapshot.data,
          actions: <Widget>[
            Builder(
              builder: (context) => bloc.navigationProvider.currentNavigation == home ?
                homeCalendar(context):otherCalendar(context) //if it's not 0 we return an empty widget
            )
          ],
        ),
        drawer: DrawerNavigation(),
        body: homeScreen()
      );
    }
  );
}

颤振中appbar的height属性中的streambuilder

2 个答案: