WebView的用法

基礎用法很簡單..

webView = (WebView) findViewById(R.id.web_view);
webView.getSettings().setJavaScriptEnabled(true);
webView.setWebViewClient(new WebViewClient() {
  @Override
  public boolean shouldOverrideUrlLoading(WebView view, Stringurl) {
    view.loadUrl(url); // 根據(jù)傳入的參數(shù)再去加載新的網(wǎng)頁
    return true; // 表示當前WebView可以處理打開新網(wǎng)頁的請求抛猫，不用借助系統(tǒng)瀏覽器
  }
 });
webView.loadUrl("http://www.baidu.com");

網(wǎng)絡訪問需要權限:

android.permission.INTERNET

10.2使用HTTP協(xié)議訪問網(wǎng)絡

Android中發(fā)送HTTP請求一般通過HttpURLConnection和HttpClient.

首先需要獲取到 HttpURLConnection 的實例少欺，一般只需 new 出一個 URL 對象，并傳入目標的網(wǎng)絡地址抡锈，然后調用一下 openConnection()方法即可.

URL url = new URL("http://www.baidu.com");
HttpURLConnection connection = (HttpURLConnection) url.openConnection();

獲取HttpURLConnection實例后設置HTTP請求方法,常用是是Get和Post.Get表示獲取數(shù)據(jù),Post表示提數(shù)據(jù).

connection.setRequestMethod("GET");

之后就可以設置連接超時,讀取超時的毫秒數(shù)或者服務器希望得到的消息頭等.
在調用getInputStream()就可以獲得服務器返回的輸入流.

InputStream in = connection.getInputStream();

最后可以調用disconnect()關閉該HTTP連接.

Post示例:

connection.setRequestMethod("POST");
DataOutputStream out = new DataOutputStream(connection.getOutputStream());
out.writeBytes("username=admin&password=123456");

10.2.2 使用HttpClient

Android6.0后已廢棄.

10.3解析XML格式數(shù)據(jù)

10.3.1Pull解析方式

private void parseXMLWithPull(String xmlData) {
  try {
    XmlPullParserFactory factory = XmlPullParserFactory.newInstance();
    XmlPullParser xmlPullParser = factory.newPullParser();
    xmlPullParser.setInput(new StringReader(xmlData));
    int eventType = xmlPullParser.getEventType();
    String id = "";
    String name = "";
    String version = "";
    while (eventType != XmlPullParser.END_DOCUMENT) {
      String nodeName = xmlPullParser.getName();
       switch (eventType) {
          // 開始解析某個結點
        case XmlPullParser.START_TAG: {
          if ("id".equals(nodeName)) {
            id = xmlPullParser.nextText();
          } else if ("name".equals(nodeName)) {
            name = xmlPullParser.nextText();
          } else if ("version".equals(nodeName)) {
            version = xmlPullParser.nextText();
          }
          break;
         }
        // 完成解析某個結點
        case XmlPullParser.END_TAG: {
          if ("app".equals(nodeName)) {
            Log.d("MainActivity", "id is " + id);
            Log.d("MainActivity", "name is " + name);
            Log.d("MainActivity", "version is " + version);
          }
          break;
        }
        default:
          break;
      }
      eventType = xmlPullParser.next();
    }
   } catch (Exception e) {
    e.printStackTrace();
   }
}

獲取的數(shù)據(jù)不對(sad臉

10.3.2SAX解析方式

新建一個類繼承DefaultHandle,重寫startDocument(),startElement(),characters(),endElement(),endDocument()五個方法.

• startDocument()方法會在開始 XML 解析的時候調用.
• startElement()方法會在開始解析某個結點的時候調用.
• characters()方法會在獲取結點中內容的時候調用.
• endElement()方法會在完成解析某個結點的時候調用.
• endDocument()方法會在完成整個 XML 解析的時候調用.

其中恩敌， startElement()瞬测、 characters()和 endElement()這三個方法是有參數(shù)的，從 XML 中解析出的數(shù)據(jù)就會以參數(shù)的形式傳入到這些方法中纠炮。需要注意的是月趟，在獲取結點中的內容時， characters()方法可能會被調用多次恢口，一些換行符也被當作內容解析出來孝宗，我們需要針對這種情況在代碼中做好控制
示例:

public class ContentHandler extends DefaultHandler {
  private String nodeName;
  private StringBuilder id;
  private StringBuilder name;
  private StringBuilder version;
  @Override
  public void startDocument() throws SAXException {
    id = new StringBuilder();
    name = new StringBuilder();
    version = new StringBuilder();
  }
  @Override
  public void startElement(String uri, String localName, String qName,Attributes attributes) throws SAXException {
    // 記錄當前結點名
    nodeName = localName;
  }
  @Override
  public void characters(char[] ch, int start, int length)   throwsSAXException {
    // 根據(jù)當前的結點名判斷將內容添加到哪一個StringBuilder對象中
    if ("id".equals(nodeName)) {
      id.append(ch, start, length);
    } else if ("name".equals(nodeName)) {
      name.append(ch, start, length);
    } else if ("version".equals(nodeName)) {
      version.append(ch, start, length);
    }
  }
  @Override
  public void endElement(String uri, String localName, String   qName) throwsSAXException {
    if ("app".equals(localName)) {
      Log.d("ContentHandler", "id is " + id.toString().trim());
      Log.d("ContentHandler", "name is " + name.toString().trim());
      Log.d("ContentHandler", "version is " +     version.toString().trim());
    // 最后要將StringBuilder清空掉id.setLength(0);
      name.setLength(0);
      version.setLength(0);
    }
  }
  @Override
  public void endDocument() throws SAXException {
  }
}

private void parseXMLWithSAX(String xmlData) {
  try {
    SAXParserFactory factory = SAXParserFactory.newInstance();
    XMLReader xmlReader =   factory.newSAXParser().getXMLReader();
    ContentHandler handler = new ContentHandler();
    // 將ContentHandler的實例設置到XMLReader中  
    xmlReader.setContentHandler(handler);
    // 開始執(zhí)行解析
    xmlReader.parse(new InputSource(new   StringReader(xmlData)));
  } catch (Exception e) {
    e.printStackTrace();
  }
}

10.4解析JSON格式數(shù)據(jù)

JSON相對于xml體積更小,但是語義較差,沒xml直觀.解析JSON可以使用官方提供的 JSONObject，也可以使用谷歌的開源庫 GSON耕肩∫蚋荆或者第三方的開源庫如 Jackson、 FastJSON .

10.4.1使用JSONObject

10.4.2使用GSON

新建類,包含標簽.

public class App {
  private String id;
  private String name;
  private String version;
  public String getId() {
    return id;
  }
  public void setId(String id) {
    this.id = id;
  }
  public String getName() {
    return name;
  }
  public void setName(String name) {
    this.name = name;
  }
  public String getVersion() {
    return version;
  }
  public void setVersion(String version) {
    this.version = version;
  }
}

使用方法:

private void parseJSONWithGSON(String jsonData) {
  Gson gson = new Gson();
  List<App> appList = gson.fromJson(jsonData, new TypeToken<List<App>>() {}.getType());
  for (App app : appList) {
    Log.d("MainActivity", "id is " + app.getId());
    Log.d("MainActivity", "name is " + app.getName());
    Log.d("MainActivity", "version is " + app.getVersion());
  }
}

10.5 網(wǎng)絡編程的最佳實踐

可以把所有的網(wǎng)絡操作提取到一個公共的類中,并提供靜態(tài)方法.
網(wǎng)絡請求通常都是屬于耗時操作猿诸，而 sendHttpRequest()方法的內部并沒有開啟線程婚被，這樣就有可能導致在調用 sendHttpRequest()方法的時候使得主線程被阻塞住。若開啟線程,則sendHttpRequest()會在服務器相應前執(zhí)行結束而無法返回相應的數(shù)據(jù).組要使用回調機制.
例如:
定義接口:

public interface HttpCallbackListener {
  void onFinish(String response);
  void onError(Exception e);
}

實現(xiàn)接口:

public class HttpUtil {
  public static void sendHttpRequest(final String address, final HttpCallbackListener listener) {
    new Thread(new Runnable() {
      @Override
      public void run() {
        HttpURLConnection connection = null;
        try {
          URL url = new URL(address);
          connection = (HttpURLConnection) url.openConnection();
          connection.setRequestMethod("GET");
          connection.setConnectTimeout(8000);
          connection.setReadTimeout(8000);
          connection.setDoInput(true);
          connection.setDoOutput(true);
          InputStream in = connection.getInputStream();
          BufferedReader reader = new       BufferedReader(newInputStreamReader(in));
          StringBuilder response = new StringBuilder();
          String line;
          while ((line = reader.readLine()) != null) {
            response.append(line);
          }
          if (listener != null) {
            // 回調onFinish()方法
            listener.onFinish(response.toString());
          }
        } catch (Exception e) {
          if (listener != null) {
            //回調onError()方法
            listener.onError(e);
          }
        } finally {
          if (connection != null) {
            connection.disconnect();
          }
        }
      }
    }).start();
  }
}

需要發(fā)起HTTP請求時:

String address = "http://www.baidu.com";
String response = HttpUtil.sendHttpRequest(address);