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();
}
}
移动设备上的一个重要用例是确保存在实际连接。当移动用户使用“专属门户”进入Wifi网络时，这是一个常见的问题，他们需要在其中登录。我在后台使用这个阻塞功能来确保连接存在。
/*
* Not Thread safe. Blocking thread. Returns true if it
* can connect to URL, false and exception is logged.
*/
public boolean checkConnectionHttps(String url){
boolean responded = false;
HttpGet requestTest = new HttpGet(url);
HttpParams params = new BasicHttpParams();
HttpConnectionParams.setConnectionTimeout(params, 3000);
HttpConnectionParams.setSoTimeout(params, 5000);
DefaultHttpClient client = new DefaultHttpClient(params);
try {
client.execute(requestTest);
responded = true;
} catch (ClientProtocolException e) {
Log.w(MainActivity.TAG,"Unable to connect to " + url + " " + e.toString());
} catch (IOException e) {
Log.w(MainActivity.TAG,"Unable to connect to " + url + " " + e.toString());
e.printStackTrace();
}
return responded;
}
非常重要的是检查我们是否与isAvailable()有连接，以及是否可能与isConnected()建立连接
private static ConnectivityManager manager;
public static boolean isOnline(Context context) {
ConnectivityManager connectivityManager = (ConnectivityManager) context.getSystemService(Context.CONNECTIVITY_SERVICE);
NetworkInfo networkInfo = connectivityManager.getActiveNetworkInfo();
return networkInfo != null && networkInfo.isAvailable() && networkInfo.isConnected();
}
你可以取消网络活动WiFi的类型:
public static boolean isConnectedWifi(Context context) {
ConnectivityManager connectivityManager = (ConnectivityManager) context.getSystemService(Context.CONNECTIVITY_SERVICE);
NetworkInfo networkInfo = connectivityManager.getActiveNetworkInfo();
return networkInfo != null && networkInfo.getType() == ConnectivityManager.TYPE_WIFI;
}
或手机Móvil:
public static boolean isConnectedMobile(Context context) {
ConnectivityManager connectivityManager = (ConnectivityManager) context.getSystemService(Context.CONNECTIVITY_SERVICE);
NetworkInfo networkInfo = connectivityManager.getActiveNetworkInfo();
return networkInfo != null && networkInfo.getType() == ConnectivityManager.TYPE_MOBILE;
}
不要忘记权限:
<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
<uses-permission android:name="android.permission.INTERNET" />
我已经应用了@Levit提供的解决方案，并创建了不会调用额外Http请求的函数。
它将解决无法解析主机的错误
public static boolean isInternetAvailable(Context context) {
ConnectivityManager cm = (ConnectivityManager) context.getSystemService(Context.CONNECTIVITY_SERVICE);
NetworkInfo activeNetwork = cm.getActiveNetworkInfo();
if (activeNetwork == null) return false;
switch (activeNetwork.getType()) {
case ConnectivityManager.TYPE_WIFI:
if ((activeNetwork.getState() == NetworkInfo.State.CONNECTED ||
activeNetwork.getState() == NetworkInfo.State.CONNECTING) &&
isInternet())
return true;
break;
case ConnectivityManager.TYPE_MOBILE:
if ((activeNetwork.getState() == NetworkInfo.State.CONNECTED ||
activeNetwork.getState() == NetworkInfo.State.CONNECTING) &&
isInternet())
return true;
break;
default:
return false;
}
return false;
}
private static boolean isInternet() {
Runtime runtime = Runtime.getRuntime();
try {
Process ipProcess = runtime.exec("/system/bin/ping -c 1 8.8.8.8");
int exitValue = ipProcess.waitFor();
Debug.i(exitValue + "");
return (exitValue == 0);
} catch (IOException | InterruptedException e) {
e.printStackTrace();
}
return false;
}
现在叫它，
if (!isInternetAvailable(getActivity())) {
//Show message
} else {
//Perfoem the api request
}
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)
