将 StreamBuilder 转换为 StreamProvider

Question

我有这样一个 StreamBuilder：

StreamBuilder<List<AuthInfo>>(
            stream: myDatabase.authInfosDao.watch(),
            builder: (context, snapshot) => (snapshot.data?.length ?? 0) > 0
                ? Home()
                : Auth()),

我想将其重做为 Stream Provider，结果就是这样：

StreamProvider<List<AuthInfo>>.value(
            value: myDatabase.authInfosDao.watch(),
            initialData: [],
            builder: (BuildContext context, AsyncSnapshop snapshot)...

我不知道如何使用“值”中的数据来加载所需的页面，因为 StreamProvider 中没有快照

Answer 1

StreamProvider<List<AuthInfo>>.value(
            value: myDatabase.authInfosDao.watch(),
            initialData: [],
            child: Consumer<List<AuthInfo>>(builder: (context, data, _) {

}, );

Answer 2

每次新数据到达流时，StreamProvider 都会重建小部件。它的功能类似于 ChangeNotificationProvider，它不会生成新的更改放置更新提供程序正在侦听的数据。

dependencies:
  flutter:
    sdk: flutter
  provider: ^6.0.2

import 'package:flutter/material.dart';
import 'package:provider/provider.dart';

void main() {
  runApp(
    const MyApp());
}

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

  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return
    StreamProvider<ModelObject>(
      initialData: ModelObject(value:0),
      create:(_)=>createStream(),
      child:  MaterialApp(
        home: Test_StreamProviderWidget(),
      ));
    
  }
}

class ModelObject{

  ModelObject({this.value});
  int ? value;
}
Stream<ModelObject> createStream(){
  return 
  Stream<ModelObject>.periodic( Duration(seconds:1), (currentPeriodicValue)=>ModelObject(value:currentPeriodicValue+1)).take(10000);
}

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

  @override
  State<Test_StreamProviderWidget> createState() => _Test_StreamProviderWidgetState();
}

class _Test_StreamProviderWidgetState extends State<Test_StreamProviderWidget> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(appBar: AppBar(title:Text("stream provider")),body:
    Consumer<ModelObject>(
      builder:(context, model, child) {
        return 
        Center(child:Column(
          mainAxisAlignment: MainAxisAlignment.center,
          crossAxisAlignment: CrossAxisAlignment.center,
          children: [
        
        Text('${model.value.toString()}',style: Theme.of(context).textTheme.headline2,)

        ],));
        
      },
    
    )
    )
    ;
  }
}

将 StreamBuilder 转换为 StreamProvider

convert StreamBuilder to StreamProvider

provider

flutter