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();
}
}
Android提供了ConnectivityManager类来了解互联网连接状态。下面的方法将是非常有用的，以了解互联网连接状态。
首先在AndroidManifest.xml中添加INTERNET和ACCESS_NETWORK_STATE权限
<uses-permission android:name="android.permission.INTERNET" />
<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
然后使用下面的方法检查设备是否连接到互联网。如果设备已连接到互联网，此方法将返回true。
public boolean isInternetAvailable(Context context) {
ConnectivityManager connectivityManager = (ConnectivityManager)
context.getSystemService(Context.CONNECTIVITY_SERVICE);
NetworkInfo activeNetwork = connectivityManager.getActiveNetworkInfo();
return activeNetwork != null
&& activeNetwork.isConnectedOrConnecting();
}
参考链接:—http://www.androidtutorialshub.com/android-check-internet-connection-status/
The other answers that use ConnectivityManager are wrong because having a network connection doesn't mean you have internet access. For example, the user might be connected to a coffee shop's WiFi portal but can't get to the internet. To check that the internet is accessible you have to try to connect to an actual server. Normally when you want to do this you have a specific server in mind that you want to connect to, so go ahead and check if you can connect to that server. Here's a simple method for checking connectivity to a server.
private boolean isOnTheInternet() {
try {
URLConnection urlConnection = new URL("http://yourserver").openConnection();
urlConnection.setConnectTimeout(400);
urlConnection.connect();
return true;
} catch (Exception e) {
return false;
}
}
设置ConnectTimeout的原因是，否则它默认为TCP超时，可以有很多秒长。
还要注意的是，Android不允许你在主线程上运行这个程序。
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;
}
只需创建下面的类来检查internet连接:
public class ConnectionStatus {
private Context _context;
public ConnectionStatus(Context context) {
this._context = context;
}
public boolean isConnectionAvailable() {
ConnectivityManager connectivity = (ConnectivityManager) _context
.getSystemService(Context.CONNECTIVITY_SERVICE);
if (connectivity != null) {
NetworkInfo[] info = connectivity.getAllNetworkInfo();
if (info != null)
for (int i = 0; i < info.length; i++)
if (info[i].getState() == NetworkInfo.State.CONNECTED) {
return true;
}
}
return false;
}
}
该类仅包含一个返回连接状态布尔值的方法。因此，简单来说，如果该方法找到一个到Internet的有效连接，则返回值为true，否则为false，如果没有找到有效连接。
MainActivity中的下面的方法调用前面描述的方法的结果，并提示用户进行相应的操作:
public void addListenerOnWifiButton() {
Button btnWifi = (Button)findViewById(R.id.btnWifi);
iia = new ConnectionStatus(getApplicationContext());
isConnected = iia.isConnectionAvailable();
if (!isConnected) {
btnWifi.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
startActivity(new Intent(Settings.ACTION_WIFI_SETTINGS));
Toast.makeText(getBaseContext(), "Please connect to a hotspot",
Toast.LENGTH_SHORT).show();
}
});
}
else {
btnWifi.setVisibility(4);
warning.setText("This app may use your mobile data to update events and get their details.");
}
}
在上面的代码中，如果结果为假，(因此没有互联网连接，用户将被带到Android wi-fi面板，在那里他将被提示连接到wi-fi热点。
下面是我使用的方法:
public boolean isNetworkAvailable(final Context context) {
return ((ConnectivityManager) context.getSystemService(Context.CONNECTIVITY_SERVICE)).getActiveNetworkInfo() != null;
}
更好的是，检查确保它是“连接”的:
public boolean isNetworkAvailable(final Context context) {
final ConnectivityManager connectivityManager = ((ConnectivityManager) context.getSystemService(Context.CONNECTIVITY_SERVICE));
return connectivityManager.getActiveNetworkInfo() != null && connectivityManager.getActiveNetworkInfo().isConnected();
}
下面是如何使用该方法:
if (isNetworkAvailable(context)) {
// code here
} else {
// code
}
需要许可:
<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
https://stackoverflow.com/a/16124915/950427
