Training—Performing Network Operations

阅读：http://developer.android.com/training/basics/network-ops/index.html

 

首先，声明权限

<uses-permission android:name="android.permission.INTERNET" />
<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />

检测网络情况：

public void myClickHandler(View view) {
    ...
    ConnectivityManager connMgr = (ConnectivityManager) 
        getSystemService(Context.CONNECTIVITY_SERVICE);
    NetworkInfo networkInfo = connMgr.getActiveNetworkInfo();
    if (networkInfo != null && networkInfo.isConnected()) {
        // fetch data
    } else {
        // display error
    }
    ...
}

官方接下来表示这种长时间操作的事情要放在另外的线程，累赘的就不写了，有个获取输入流的倒是可以参考下：

// Given a URL, establishes an HttpUrlConnection and retrieves
// the web page content as a InputStream, which it returns as
// a string.
private String downloadUrl(String myurl) throws IOException {
    InputStream is = null;
    // Only display the first 500 characters of the retrieved
    // web page content.
    int len = 500;
        
    try {
        URL url = new URL(myurl);
        HttpURLConnection conn = (HttpURLConnection) url.openConnection();
        conn.setReadTimeout(10000 /* milliseconds */);
        conn.setConnectTimeout(15000 /* milliseconds */);
        conn.setRequestMethod("GET");
        conn.setDoInput(true);
        // Starts the query
        conn.connect();
        int response = conn.getResponseCode();
        Log.d(DEBUG_TAG, "The response is: " + response);
        is = conn.getInputStream();

        // Convert the InputStream into a string
        String contentAsString = readIt(is, len);
        return contentAsString;
        
    // Makes sure that the InputStream is closed after the app is
    // finished using it.
    } finally {
        if (is != null) {
            is.close();
        } 
    }
}

获得流之后，或者你把它编码为图片或者是文字。

InputStream is = null;
...
Bitmap bitmap = BitmapFactory.decodeStream(is);
ImageView imageView = (ImageView) findViewById(R.id.image_view);
imageView.setImageBitmap(bitmap);


/////////////////////////////////////


// Reads an InputStream and converts it to a String.
public String readIt(InputStream stream, int len) throws IOException, UnsupportedEncodingException {
    Reader reader = null;
    reader = new InputStreamReader(stream, "UTF-8");        
    char[] buffer = new char[len];
    reader.read(buffer);
    return new String(buffer);
}

---

联网操作之前检测下网络情况是很有必要的，一般需要用到

• ConnectivityManager: Answers queries about the state of network connectivity. It also notifies applications when network connectivity changes.
• NetworkInfo: Describes the status of a network interface of a given type (currently either Mobile or Wi-Fi).

private static final String DEBUG_TAG = "NetworkStatusExample";
...      
ConnectivityManager connMgr = (ConnectivityManager) 
        getSystemService(Context.CONNECTIVITY_SERVICE);
NetworkInfo networkInfo = connMgr.getNetworkInfo(ConnectivityManager.TYPE_WIFI); 
boolean isWifiConn = networkInfo.isConnected();
networkInfo = connMgr.getNetworkInfo(ConnectivityManager.TYPE_MOBILE);
boolean isMobileConn = networkInfo.isConnected();
Log.d(DEBUG_TAG, "Wifi connected: " + isWifiConn);
Log.d(DEBUG_TAG, "Mobile connected: " + isMobileConn);

上面的例子就很好的说明了两个类的用法。

如果只是想测试下联网了没而不需要联网类型，那么：

public boolean isOnline() {
    ConnectivityManager connMgr = (ConnectivityManager) 
            getSystemService(Context.CONNECTIVITY_SERVICE);
    NetworkInfo networkInfo = connMgr.getActiveNetworkInfo();
    return (networkInfo != null && networkInfo.isConnected());
}  

---

这一节的最后教你怎么解析XML:http://developer.android.com/training/basics/network-ops/xml.html

不过目前一般都是使用json吧，所以就不在深入了。