Node.js NodeJs请求Dart中的回调

我正在尝试将下面的Node.js代码段转换为Dart。在我的转换中，只要有响应，就会打印“data returned…”消息，这与Node.js版本不同，Node.js版本会等待页面完成请求的2秒延迟

Node.js

var http = require('http')    
function fetchPage() {
  console.log('fetching page');
  http.get({ host: 'trafficjamapp.herokuapp.com', path: '/?delay=2000' }, function(res) {
    console.log('data returned from requesting page');
  }).on('error', function(e) {
    console.log("There was an error" + e);
  });
}

飞镖

---

如何在Dart中实现与在Node中相同的延迟打印？提前感谢。

您可以在

onResponse

回调的文档中找到：

当接收到响应的所有头并准备好接收数据时，将调用回调

所以它是这样工作的：

connection.onResponse = (res) {
  print('Headers received, can read the body now');
  var in = res.inputStream;

  in.onData = () {
    // this can be called multiple times
    print('Received data');
    var data = in.read();
    // do something with data, probably?
  };
  in.onClosed = () {
    // this is probably the event you are interested in
    print('No more data available');
  };
  in.onError = (e) {
    print('Error reading data: $e');
  };
};

---

您的Dart代码几乎正确，但有一个bug。您应该使用

query

命名参数，而不是

path

。我真的不知道用你的代码调用哪个Url，但是响应有一个

400

状态代码。为了提高可读性，还可以使用

Uri.fromString

构造函数

此外，您可以省略

onRequest

设置，因为未定义

onRequest

时会执行相同的代码

代码如下：

import 'dart:io';
import 'dart:uri';

main() {
  print('fetching page');
  //var uri = new Uri.fromString('http://trafficjamapp.herokuapp.com/?delay=2000');
  var uri = new Uri.fromComponents(scheme:'http',
      domain: 'trafficjamapp.herokuapp.com', query: 'delay=2000');
  var client = new HttpClient();
  var connection = client.getUrl(uri);
  connection.onResponse = (HttpClientResponse res){
    print('data returned from requesting page with status ${res.statusCode}');
  };
  connection.onError = (e) => print('There was an error' ' $e');
}

---

谢谢现在我明白了，我可以在路径命名参数前面添加“/”以使我的代码也能正常工作，但是使用query name参数可以使意图更加清晰。谢谢。现在我了解了如何使用流并获得关闭的事件。我只需重命名'in'变量，并将'/'添加到原始路径的开头。

import 'dart:io';
import 'dart:uri';

main() {
  print('fetching page');
  //var uri = new Uri.fromString('http://trafficjamapp.herokuapp.com/?delay=2000');
  var uri = new Uri.fromComponents(scheme:'http',
      domain: 'trafficjamapp.herokuapp.com', query: 'delay=2000');
  var client = new HttpClient();
  var connection = client.getUrl(uri);
  connection.onResponse = (HttpClientResponse res){
    print('data returned from requesting page with status ${res.statusCode}');
  };
  connection.onError = (e) => print('There was an error' ' $e');
}