我得到了一个AsyncTask,应该检查对主机名的网络访问。但是doInBackground()永远不会超时。有人知道吗?

public class HostAvailabilityTask extends AsyncTask<String, Void, Boolean> {

    private Main main;

    public HostAvailabilityTask(Main main) {
        this.main = main;
    }

    protected Boolean doInBackground(String... params) {
        Main.Log("doInBackground() isHostAvailable():"+params[0]);

        try {
            return InetAddress.getByName(params[0]).isReachable(30); 
        } catch (UnknownHostException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
        return false;       
    }

    protected void onPostExecute(Boolean... result) {
        Main.Log("onPostExecute()");

        if(result[0] == false) {
            main.setContentView(R.layout.splash);
            return;
        }

        main.continueAfterHostCheck();
    }   
}

当前回答

我已经尝试了近5+不同的android方法,发现这是谷歌提供的最佳解决方案,特别是android:

  try {
  HttpURLConnection urlConnection = (HttpURLConnection)
  (new URL("http://clients3.google.com/generate_204")
  .openConnection());
  urlConnection.setRequestProperty("User-Agent", "Android");
  urlConnection.setRequestProperty("Connection", "close");
  urlConnection.setConnectTimeout(1500);
  urlConnection.connect();
  if (urlConnection.getResponseCode() == 204 &&
  urlConnection.getContentLength() == 0) {
  Log.d("Network Checker", "Successfully connected to internet");
  return true;
  }
  } catch (IOException e) {
  Log.e("Network Checker", "Error checking internet connection", e);
  }

它比任何其他可用的解决方案都更快、高效和准确。

其他回答

从以下链接找到并修改(!):

在你的manifest文件中至少添加:

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

如果您正在访问它,您可能已经拥有INTERNET权限。那么一个允许测试连通性的布尔函数是:

private boolean checkInternetConnection() {
    ConnectivityManager cm = (ConnectivityManager) getSystemService(Context.CONNECTIVITY_SERVICE);
    // test for connection
    if (cm.getActiveNetworkInfo() != null
            && cm.getActiveNetworkInfo().isAvailable()
            && cm.getActiveNetworkInfo().isConnected()) {
        return true;
    } else {
        Log.v(TAG, "Internet Connection Not Present");
        return false;
    }
}

我使用这段代码而不是InetAddress:

    try {

        URL url = new URL("http://"+params[0]);

        HttpURLConnection urlc = (HttpURLConnection) url.openConnection();
        urlc.setRequestProperty("User-Agent", "Android Application:"+Z.APP_VERSION);
        urlc.setRequestProperty("Connection", "close");
        urlc.setConnectTimeout(1000 * 30); // mTimeout is in seconds
        urlc.connect();
        if (urlc.getResponseCode() == 200) {
            Main.Log("getResponseCode == 200");
            return new Boolean(true);
        }
    } catch (MalformedURLException e1) {
        // TODO Auto-generated catch block
        e1.printStackTrace();
    } catch (IOException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }

对我来说,在Activity类中检查连接状态并不是一个好的实践,因为

ConnectivityManager cm =
    (ConnectivityManager) getSystemService(Context.CONNECTIVITY_SERVICE);

应该在那里调用,或者您需要下推您的活动实例(上下文)到连接处理程序类,以能够检查那里的连接状态 当没有可用的连接(wifi,网络)时,我捕捉到UnknownHostException异常:

JSONObject jObj = null;
Boolean responded = false;
HttpGet requestForTest = new HttpGet("http://myserver.com");
try {
    new DefaultHttpClient().execute(requestForTest);
    responded = true;
} catch (UnknownHostException e) {
    jObj = new JSONObject();
    try {
        jObj.put("answer_code", 1);
        jObj.put("answer_text", "No available connection");
    } catch (Exception e1) {}
    return jObj;
} catch (IOException e) {
    e.printStackTrace();
}

通过这种方式,我可以处理这种情况连同其他情况在同一类(我的服务器总是响应回json字符串)

这段代码将帮助您找到互联网是否打开。

public final boolean isInternetOn() {
        ConnectivityManager conMgr = (ConnectivityManager) this.con
                .getSystemService(Context.CONNECTIVITY_SERVICE);
        NetworkInfo info = conMgr.getActiveNetworkInfo();
        return (info != null && info.isConnected());
}

此外,您应该提供以下权限

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

如果设备处于飞行模式(或者假设在没有可用网络的其他情况下),cm.getActiveNetworkInfo()将为空,因此您需要添加一个空检查。

修改(Eddie的解决方案)如下:

public boolean isOnline() {
    ConnectivityManager cm =
        (ConnectivityManager) getSystemService(Context.CONNECTIVITY_SERVICE);
    NetworkInfo netInfo = cm.getActiveNetworkInfo();
    return netInfo != null && netInfo.isConnectedOrConnecting();
}

在AndroidManifest.xml中添加以下权限:

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

还有一点,如果你在给定的时间点绝对需要一个网络连接,那么使用netInfo.isConnected()而不是netInfo.isConnectedOrConnecting可能会更好。不过,我想这取决于个人用例。