StreamBuilder 流构造器

可指定一个stream对象，能够监听异步执行的状态，并在构造器中根据状态构建不同的界面。

相关组件

FutureBuilder

StreamBuilder基本使用

【stream】 : 子组件 【Stream】
【initialData】 : 初始数据 【T】
【builder】 : 点击事件 【AsyncWidgetBuilder】

import 'dart:async';
import 'package:flutter/material.dart';
class CustomStreamBuilder extends StatefulWidget {
  @override
  _CustomStreamBuilderState createState() => _CustomStreamBuilderState();
}

class _CustomStreamBuilderState extends State<CustomStreamBuilder> {
  CountGenerator _generator = CountGenerator()..increment();

  @override
  void dispose() {
    _generator.dispose(); //关闭控制器
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return Container(
      child: Row(
        mainAxisSize: MainAxisSize.min,
        children: <Widget>[
          FlatButton(
            color: Colors.blue,
            shape: CircleBorder(
              side: BorderSide(width: 2.0, color: Color(0xFFFFDFDFDF)),
            ),
            child: Icon(
              Icons.add,
              color: Colors.white,
            ),
            onPressed: () async {
              await _generator.increment();
            },
          ),
          _buildStreamBuilder(),
          FlatButton(
            color: Colors.blue,
            shape: CircleBorder(
              side: BorderSide(width: 2.0, color: Color(0xFFFFDFDFDF)),
            ),
            child: Icon(
              Icons.remove,
              color: Colors.white,
            ),
            onPressed: () async {
              await _generator.minus();
            },
          ),
        ],
      ),
    );
  }

  Widget _buildStreamBuilder() => StreamBuilder<int>(
      stream: _generator.state,
      builder: (BuildContext context, AsyncSnapshot snap) {
        print(snap);
        if (snap.connectionState == ConnectionState.done) {
          return Text('Done');
        }
        if (snap.connectionState == ConnectionState.active) {
          return Text(
            snap.data.toString(),
            style: Theme.of(context).textTheme.display1,
          );
        }
        if (snap.connectionState == ConnectionState.waiting) {
          return CircularProgressIndicator();
        }
        if (snap.hasError) {
          return Text('Error');
        }
        return Container();
      });
}

class CountGenerator {
  int _count = 0; //计数器数据
  final StreamController<int> _controller = StreamController(); //控制器

  Stream<int> get state => _controller.stream; //获取状态流
  int get count => _count; //获取计数器数据

  void dispose() {//关闭控制器
    _controller.close();
  }

  Future<void> increment() async {//增加记数方法
    _controller.add(++_count);
  }

  Future<void> minus() async {//增加记数方法
    _controller.add(--_count);
  }
}