网络传递数据

2016-8-1 11:56| 发布者: admin| 查看: 2827| 评论: 0

摘要: Many mobile apps need to load resources from a remote URL. You may want to make a POST request to a REST API, or you may simply need to fetch a chunk of static content from another server.使用FetchRea ...

Many mobile apps need to load resources from a remote URL. You may want to make a POST request to a REST API, or you may simply need to fetch a chunk of static content from another server.

使用Fetch

React Native provides the Fetch API for your networking needs. Fetch will seem familiar if you have used XMLHttpRequest or other networking APIs before. You may refer to MDN's guide on Using Fetch for additional information.

发起网络请求

In order to fetch content from an arbitrary URL, just pass the URL to fetch:

fetch('https://mywebsite.com/mydata.json')

Fetch also takes an optional second argument that allows you to customize the HTTP request. You may want to specify additional headers, or make a POST request:

fetch('https://mywebsite.com/endpoint/', {
  method: 'POST',
  headers: {
    'Accept': 'application/json',
    'Content-Type': 'application/json',
  },
  body: JSON.stringify({
    firstParam: 'yourValue',
    secondParam: 'yourOtherValue',
  })
})

Take a look at the Fetch Request docs for a full list of properties.

处理服务器的响应数据

The above examples show how you can make a request. In many cases, you will want to do something with the response.

Networking is an inherently asynchronous operation. Fetch methods will return a Promise that make it straightforward to write code that works in an asynchronous manner:

  getMoviesFromApiAsync() {
    return fetch('http://facebook.github.io/react-native/movies.json')
      .then((response) => response.json())
      .then((responseJson) => {
        return responseJson.movies;
      })
      .catch((error) => {
        console.error(error);
      });
  }

You can also use ES7's async/await syntax in React Native app:

  async getMoviesFromApi() {
    try {
      let response = await fetch('http://facebook.github.io/react-native/movies.json');
      let responseJson = await response.json();
      return responseJson.movies;
    } catch(error) {
      console.error(error);
    }
  }

Don't forget to catch any errors that may be thrown by fetch, otherwise they will be dropped silently.

Using Other Networking Libraries

The XMLHttpRequest API is built in to React Native. This means that you can use third party libraries such as frisbee or axios that depend on it, or you can use the XMLHttpRequest API directly if you prefer.

var request = new XMLHttpRequest();
request.onreadystatechange = (e) => {
  if (request.readyState !== 4) {
    return;
  }

  if (request.status === 200) {
    console.log('success', request.responseText);
  } else {
    console.warn('error');
  }
};

request.open('GET', 'https://mywebsite.com/endpoint/');
request.send();

The security model for XMLHttpRequest is different than on web as there is no concept of CORS in native apps.

WebSocket支持

React Native还支持WebSocket,这种协议可以在单个TCP连接上提供全双工的通信信道。

var ws = new WebSocket('ws://host.com/path');

ws.onopen = () => {
  // connection opened

  ws.send('something'); // send a message
};

ws.onmessage = (e) => {
  // a message was received
  console.log(e.data);
};

ws.onerror = (e) => {
  // an error occurred
  console.log(e.message);
};

ws.onclose = (e) => {
  // connection closed
  console.log(e.code, e.reason);
};

Your app can now display all sorts of data and you may soon need to organize this content into several screens. To manage the transition between these screens, you will need to learn about navigators.


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