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;
}
不需要太复杂。最简单的框架方式是使用ACCESS_NETWORK_STATE权限并创建一个连接的方法
public boolean isOnline() {
ConnectivityManager cm =
(ConnectivityManager) getSystemService(Context.CONNECTIVITY_SERVICE);
return cm.getActiveNetworkInfo() != null &&
cm.getActiveNetworkInfo().isConnectedOrConnecting();
}
如果您有特定的主机和连接类型(wifi/移动)，也可以使用requestRouteToHost。
你还需要:
<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
在你的android清单中。
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)
检查这段代码…这对我很有用:)
public static void isNetworkAvailable(final Handler handler, final int timeout) {
// ask fo message '0' (not connected) or '1' (connected) on 'handler'
// the answer must be send before before within the 'timeout' (in milliseconds)
new Thread() {
private boolean responded = false;
@Override
public void run() {
// set 'responded' to TRUE if is able to connect with google mobile (responds fast)
new Thread() {
@Override
public void run() {
HttpGet requestForTest = new HttpGet("http://m.google.com");
try {
new DefaultHttpClient().execute(requestForTest); // can last...
responded = true;
}
catch (Exception e) {
}
}
}.start();
try {
int waited = 0;
while(!responded && (waited < timeout)) {
sleep(100);
if(!responded ) {
waited += 100;
}
}
}
catch(InterruptedException e) {} // do nothing
finally {
if (!responded) { handler.sendEmptyMessage(0); }
else { handler.sendEmptyMessage(1); }
}
}
}.start();
}
然后，我定义处理程序:
Handler h = new Handler() {
@Override
public void handleMessage(Message msg) {
if (msg.what != 1) { // code if not connected
} else { // code if connected
}
}
};
.．.并启动测试:
isNetworkAvailable(h,2000); // get the answser within 2000 ms
我做了这个代码，它是最简单的，它只是一个布尔值。
通过询问if(isOnline()){
如果存在连接，并且可以连接到页面，则会得到状态代码200(稳定连接)。
确保添加正确的INTERNET和ACCESS_NETWORK_STATE权限。
public boolean isOnline() {
ConnectivityManager cm = (ConnectivityManager) getSystemService(Context.CONNECTIVITY_SERVICE);
NetworkInfo netInfo = cm.getActiveNetworkInfo();
if (netInfo != null && netInfo.isConnected()) {
try {
URL url = new URL("http://www.google.com");
HttpURLConnection urlc = (HttpURLConnection) url.openConnection();
urlc.setConnectTimeout(3000);
urlc.connect();
if (urlc.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();
}
}
return false;
}
