[Android App Development] 03. Network Programming

Objective

• Network programming is not difficult, mainly to master a few points can be.
• Use HttpURLConnection for network programming.
• If you are doing network programming on the main thread, Android throws an exception, and another thread is doing the logical operation of the network code.
• To update the UI interface, use handler and message. Learn about the looper mechanism.
• Familiarize yourself with GET requests and post requests, and know the difference.

• Let's take a few examples below to learn more about how to do network programming.

  • Network Picture Viewer
  • Smart-image-view (project), recommended to read the next source
  • Download the image , put it in the cache directory (data/data/"project package Name"/cache), about the cache directory, see [Android Application Development 02]/Use the path API read and write storage read and write files section.
  • page Source Viewer .
  Network Picture Viewer

  Determine the URL of the image

• Send HTTP request

    URL url = new URL(address);  //获取连接对象，并没有建立连接  HttpURLConnection conn = (HttpURLConnection) url.openConnection();  //设置连接和读取超时  conn.setConnectTimeout(5000);  conn.setReadTimeout(5000);  //设置请求方法，注意必须大写  conn.setRequestMethod("GET");  //建立连接，发送get请求  //conn.connect();  //建立连接，然后获取响应吗，200说明请求成功  conn.getResponseCode();

• The image of the server is returned to the browser in the form of a stream.

    //拿到服务器返回的输入流  InputStream is = conn.getInputStream();  //把流里的数据读取出来，并构造成图片  Bitmap bm = BitmapFactory.decodeStream(is);

• Set the picture to the ImageView display

    ImageView iv = (ImageView) findViewById(R.id.iv);  iv.setImageBitmap(bm);

• Add permissions

The main thread cannot be blocked

• In Android, the main thread being blocked can cause the app to not refresh the UI interface, not respond to user actions, and the user experience will be very poor

• The system throws a ANR exception when the main thread is blocked for too long

• • UI stops refreshing, app cannot respond to user action

• Time-consuming operations should not be performed on the main thread

• Anr

  • Application Not Responding

  • Apply non-responsive exception

  • When the main thread blocks too long, the ANR will be thrown

• Any time-consuming operation cannot be written in the main thread

• Because network interaction is a time-consuming operation, if the speed is slow, the code blocks, so the code for network interaction cannot run on the main thread

• The main thread is also called the UI thread, because the UI can be refreshed only in the main thread

Only the main thread can refresh the UI

• The code that refreshes the UI can only run on the main thread, and running on a child thread is not any effect

• If you need to refresh the UI in a child thread, use the Message Queuing mechanism

Message Queuing

• Looper once a message is found in the queue, it takes the message out and throws the message to the handler object, handler calls its own Handlemessage method to process the message.

• The Handlemessage method runs on the main thread

• When the main thread is created, the message queue and the polling object are created, but the Message Processor object, when it needs to be used, creates itself

• Summary: As long as Message Queuing has a message, the Handlemessage method calls

• Child threads If you need to refresh the UI, just send a message to the message queue and trigger the Handlemessage method

• A child thread sends a message using the SendMessage method of the Processor object

    //消息队列  Handler handler = new Handler(){      //主线程中有一个消息轮询器looper，不断检测消息队列中是否有新消息，如果发现有新消息，自动调用此方法，注意此方法是在主线程中运行的      public void handleMessage(android.os.Message msg) {      }  };

• Send a message to the message queue in a child thread

    //创建消息对象  Message msg = new Message();  //消息的obj属性可以赋值任何对象，通过这个属性可以携带数据  msg.obj = bm;  //what属性相当于一个标签，用于区分出不同的消息，从而运行不能的代码  msg.what = 1;  //发送消息  handler.sendMessage(msg);

• Distinguish different messages by switch statements

    public void handleMessage(android.os.Message msg) {      switch (msg.what) {      //如果是1，说明属于请求成功的消息      case 1:          ImageView iv = (ImageView) findViewById(R.id.iv);          Bitmap bm = (Bitmap) msg.obj;          iv.setImageBitmap(bm);          break;      case 2:          Toast.makeText(MainActivity.this, "请求失败", 0).show();          break;      }         }

The ability to add cached images

• Reads the data from the stream returned by the server and writes it to the local file via the file input stream.

    //1.拿到服务器返回的输入流  InputStream is = conn.getInputStream();  //2.把流里的数据读取出来，并构造成图片  FileOutputStream fos = new FileOutputStream(file);  byte[] b = new byte[1024];  int len = 0;  while((len = is.read(b)) != -1){      fos.write(b, 0, len);  }

• The code to create the bitmap object is changed to

    Bitmap bm = BitmapFactory.decodeFile(file.getAbsolutePath());

• Detects if there is a picture with the same name in the cache before each request is sent, and if so, reads the cache

Get a Web site with open source code

• This smart Picture SDK is very useful!

• Github.com

• Search Smart-image-view on GitHub

• Download Open Source Project Smart-image-view

• Label name to write package name when using custom components

    <com.sinyee.babybus.SmartImageView/>

• Use of Smartimageview

    SmartImageView siv = (SmartImageView) findViewById(R.id.siv);  siv.setImageUrl("http://192.168.1.10:8080/dd.jpg");

HTML Source File Viewer

• Send a GET request

    URL url = new URL(path);  //获取连接对象  HttpURLConnection conn = (HttpURLConnection) url.openConnection();  //设置连接属性  conn.setRequestMethod("GET");  conn.setConnectTimeout(5000);  conn.setReadTimeout(5000);  //建立连接，获取响应吗  if(conn.getResponseCode() == 200){  }

• Gets the stream returned by the server and reads the HTML source from the stream

    byte[] b = new byte[1024];  int len = 0;  ByteArrayOutputStream bos = new ByteArrayOutputStream();  while((len = is.read(b)) != -1){      //把读到的字节先写入字节数组输出流中存起来      bos.write(b, 0, len);  }  //把字节数组输出流中的内容转换成字符串  //默认使用utf-8  text = new String(bos.toByteArray());

Handling of garbled characters

• garbled appearance due to inconsistent server and client code table

    //手动指定码表  text = new String(bos.toByteArray(), "gb2312");

Submit data get method submit data

• The data submitted by the Get method is directly stitched at the end of the URL

    final String path = "http://192.168.1.104/Web/servlet/CheckLogin?name=" + name + "&pass=" + pass;

• Send a GET request, the code is the same as before

    URL url = new URL(path);  HttpURLConnection conn = (HttpURLConnection) url.openConnection();  conn.setRequestMethod("GET");  conn.setReadTimeout(5000);  conn.setConnectTimeout(5000);  if(conn.getResponseCode() == 200){  }

• The browser will URL-encode the data when it sends the request, and we need to encode the code in Chinese when we write it.

    String path = "http://192.168.1.104/Web/servlet/CheckLogin?name=" + URLEncoder.encode(name) + "&pass=" + pass;

Post mode submit data

• The post submission data is written to the server using a stream

• Two more properties in the protocol header

  • Content-type:application/x-www-form-urlencoded, describing the mimetype of the submitted data

  • CONTENT-LENGTH:32, describing the length of the submitted data

      //给请求头添加post多出来的两个属性  String data = "name=" + URLEncoder.encode(name) + "&pass=" + pass;  conn.setRequestProperty("Content-Type", "application/x-www-form-urlencoded");  conn.setRequestProperty("Content-Length", data.length() + "");

• Set the stream that allows the post request to be opened

    conn.setDoOutput(true);

• Gets the output stream of the connection object, writes the data to be submitted to the server in the stream

    OutputStream os = conn.getOutputStream();  os.write(data.getBytes());

This site article is for baby bus SD. Team Original, reproduced must be clearly noted: (the author's official website: Baby bus )
Reprinted from "Baby bus Superdo Team" original link: http://www.cnblogs.com/superdo/p/4890916.html

[Android App Development] 03. Network Programming