Flutter_05_FutureBuilder和StreamBuilder

FutureBuilder代码笔记

import 'package:flutter/material.dart';

class User {
  String name;
  int age;

  User({this.name = 'lzh', this.age = 28});

  @override
  String toString() {
    return name;
  }
}

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

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

class _FutureBuildWidgetState extends State<FutureBuildWidget> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(),
      // 设置子组件统一的文本样式
      body: DefaultTextStyle(
        style: TextStyle(fontSize: 40, color: Colors.blue),
        child: Center(
          child: FutureBuilder(
              // 设置一个初始值
              // initialData: 100,
              // 模拟一个2秒的耗时操作
              future: Future<User>.delayed(
                Duration(seconds: 2),
                () => User(),
              ),
              builder: (BuildContext context, AsyncSnapshot<User> snapshot) {
                if (snapshot.hasError) {
                  return Text('${snapshot.error}');
                }
                // 1、判断Future的状态是否完成
                if (snapshot.hasData) {
                  return Text(
                      '${snapshot.data?.name} ${snapshot.data?.age}'); // 2、获取Future返回的数据
                }
                // 设置了初始值，就不会走loading了
                return CircularProgressIndicator();
              }),
        ),
      ),
    );
  }
}

StreamBuilder代码笔记

import 'dart:async';
import 'dart:math';

import 'package:flutter/material.dart';

class StreamBuildWidget extends StatefulWidget {
  @override
  _StreamBuildWidgetState createState() => _StreamBuildWidgetState();
}

class _StreamBuildWidgetState extends State<StreamBuildWidget> {
  // 创建一个数据流
  final StreamController _streamController = StreamController.broadcast();

  // 创建一个Stream数据流
  Stream<DateTime> getDateTimeStream() async* {
    while (true) {
      await Future.delayed(Duration(seconds: 1));
      // 类似Python的yield
      yield DateTime.now();
    }
  }

  @override
  void initState() {
    super.initState();
    // 多方监听需要设置为广播数据流
    _streamController.stream.listen((event) {
      print(event);
    });
  }

  @override
  void dispose() {
    super.dispose();
    // 页面销毁时，关闭数据流
    _streamController.close();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(),
      floatingActionButton: FloatingActionButton(
        child: Icon(Icons.refresh),
        // 往数据流中放数据
        onPressed: () => _streamController.sink.add(Random().nextInt(2)),
      ),
      body: Center(
          child: Container(
        child: StreamBuilder(
          // 监听自己创建的数据流
          stream: _streamController.stream
              .where((event) => event is int) // 筛选事件
              .map((event) => event * 2) // 对事件进行封装
              .distinct(), // 事件去重
          // 事件没变的时候，build不会重新绘制
          builder: (BuildContext context, AsyncSnapshot snapshot) {
            print('build widget...');
            switch (snapshot.connectionState) {
              case ConnectionState.none:
                return Text('none');
              case ConnectionState.waiting:
                return Text('waiting');
              case ConnectionState.active:
                // 初始有数据的时候的逻辑
                if (snapshot.hasError) {
                  return Text('${snapshot.error}');
                } else {
                  return Text('${snapshot.data}');
                }
              case ConnectionState.done:
                return Text('done');
            }
          },
        ),
      )),
    );
  }
}