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等待未来一段特定的时间

future flutter async-await dart asynchronous

Pushan Gupta · 技术社区 · 7 年前

你将如何等待未来的回应一个特定的时间量?

比方说,我们发出一个httppost请求并等待它的响应,然后关闭http请求,但是,我们只等待3秒,否则就关闭请求。

你怎么做到的?

像这样的

Future makePostReq() async{
  .... 

  await http response for 3 secs

  .... 

 if(response) {
  ... Do something with it
 }

 Http.close

}

1 回复 | 直到 7 年前

Nate Bosch 7 年前

你可以用 Future.any 构造一个竞赛条件

final result = await Future.any([
  Future.value(42),
  Future.delayed(const Duration(seconds: 3))
]);

Future.timout 方法

final result = await Future.value(42).timeout(const Duration(seconds: 3));

Sanjayrajsinh 6 年前

你做起来很容易

try {
       var response = await Http.get("YourUrl").timeout(const Duration(seconds: 3));
       if(response.statusCode == 200){
          print("Success");
       }else{
          print("Something wrong");
       }
 } on TimeoutException catch (e) {
     print('Timeout');
 } on Error catch (e) {
     print('Error: $e');
 }

本例将超时设置为3秒。如果已经3秒没有收到响应,它将抛出 TimeoutException

导入此项:

import 'package:http/http.dart' as Http;
import 'dart:async';

Baker 5 年前

未来。有吗([ 异步函数

下面是一个使用Remi Future.any 首先返回的未来将被使用的解决方案。另一个被丢弃。

因此,第一个未来是您的数据收集/慢功能,另一个是当您的调用花费太长时间时的回退功能。

    dynamic result = await Future.any([
      getData(fakeDelay: seconds), // â hope this returns first
      timeoutAfter(sec: timeout, onTimeout: () => 'Timed Out!', ) // â waited too long, do this
    ]);

颤振页面中的示例

下面是颤振页面的复制/粘贴示例:

(查看调试/运行输出窗口中的消息)

import 'package:flutter/material.dart';

class FutureTimeoutPage extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Future or Timeout Page'),
      ),
      body: FutureAnyExample(),
    );
  }
}

class FutureAnyExample extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Column(
      mainAxisAlignment: MainAxisAlignment.center,
      children: [
        Text('Complete before timeout or timeout:'),
        SizedBox(height: 30,),
        Row(
          mainAxisAlignment: MainAxisAlignment.spaceEvenly,
          children: [
            ElevatedButton(onPressed: () => getDataOrTimeout(seconds: 1, timeout: 3),
                child: Text('In Time')),
            ElevatedButton(onPressed: () => getDataOrTimeout(seconds: 5, timeout: 3),
                child: Text('Too Slow'))
          ],
        )
      ],
    );
  }

  Future<void> getDataOrTimeout({int seconds, int timeout}) async {
    /// In Future.any, put as many async functions as you need.
    /// Whichever completes first, will be returned. All others are discarded
    dynamic result = await Future.any([
      getData(fakeDelay: seconds), // â hope this returns first
      timeoutAfter(sec: timeout, onTimeout: () => 'Timed Out!', ) // â waited too long, do this
    ]);

    print(result);
  }

  /// Mock of a long-running operation like getting DB data, or API call
  Future<String> getData({int fakeDelay}) async {
    return Future.delayed(Duration(seconds: fakeDelay), () => 'Data returned!');
  }

  /// Do this in case my long-running op takes too long
  /// Can run a function or just return some message
  Future<dynamic> timeoutAfter({int sec, Function() onTimeout}) async {
    return Future.delayed(Duration(seconds: sec), onTimeout);
  }
}