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();
}
}
在我目前所见过的所有方法中，最短、最干净的方法应该是:
public final static boolean isConnected( Context context )
{
final ConnectivityManager connectivityManager =
(ConnectivityManager) context.getSystemService( Context.CONNECTIVITY_SERVICE );
final NetworkInfo networkInfo = connectivityManager.getActiveNetworkInfo();
return networkInfo != null && networkInfo.isConnected();
}
PS:这不会ping任何主机，它只是检查连接状态，所以如果你的路由器没有互联网连接，而你的设备连接到它，这个方法将返回true，尽管你没有互联网。
对于实际的测试，我建议执行一个HttpHead请求(例如到www.google.com)并检查状态，如果它是200 OK，一切正常，并且您的设备有互联网连接。
Jetpack组成/芬兰湾的科特林
根据Levite的回答，我们可以在Jetpack Compose中使用这个组合:
val DNS_SERVERS = listOf("8.8.8.8", "1.1.1.1", "4.2.2.4")
const val INTERNET_CHECK_DELAY = 3000L
@Composable
fun InternetAwareComposable(
dnsServers: List<String> = DNS_SERVERS,
delay: Long = INTERNET_CHECK_DELAY,
successContent: (@Composable () -> Unit)? = null,
errorContent: (@Composable () -> Unit)? = null,
onlineChanged: ((Boolean) -> Unit)? = null
) {
suspend fun dnsAccessible(
dnsServer: String
) = try {
withContext(Dispatchers.IO) {
Runtime.getRuntime().exec("/system/bin/ping -c 1 $dnsServer").waitFor()
} == 0
} catch (e: Exception) {
false
}
var isOnline by remember { mutableStateOf(false) }
LaunchedEffect(Unit) {
while (true) {
isOnline = dnsServers.any { dnsAccessible(it) }
onlineChanged?.invoke(isOnline)
delay(delay)
}
}
if (isOnline) successContent?.invoke()
else errorContent?.invoke()
}
if(isConnected()){
Toast.makeText(getApplication(),"Thank you",Toast.LENGTH_SHORT).show();
}
else{
AlertDialog.Builder builder =
new AlertDialog.Builder(this, R.style.AppCompatAlertDialogStyle);
builder.setTitle("Amar Bhat");
builder.setMessage("Oops...You are not connected to Internet!!!");
builder.setPositiveButton("OK", null);
builder.setNegativeButton("Cancel", null);
builder.show();
//Toast.makeText(getApplication(),"You are not connected",Toast.LENGTH_SHORT).show();
}
//And outside the class define isConnected()
public boolean isConnected(){
ConnectivityManager connMgr = (ConnectivityManager) getSystemService(Activity.CONNECTIVITY_SERVICE);
NetworkInfo networkInfo = connMgr.getActiveNetworkInfo();
if (networkInfo != null && networkInfo.isConnected())
return true;
else
return false;
}
// In minifest add these permission
<uses-permission android:name="android.permission.INTERNET" />
<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
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
}
这个线程中的大多数答案只检查是否有可用的连接，但不检查该连接是否工作，其他答案不是设备范围，我的解决方案应该在每个设备上工作。
你可以在启动应用程序之前在你的主要活动中删除我的代码，它会快速确定是否有实际的互联网连接，如果有对话框将立即删除，应用程序将被启动，如果没有警报会弹出说应用程序需要互联网连接才能工作。
final AlertDialog alertDialog = new AlertDialog.Builder(this).create();
alertDialog.setTitle("Checking Connection");
alertDialog.setMessage("Checking...");
alertDialog.show();
new CountDownTimer(5000, 1000) {
@Override
public void onTick(long millisUntilFinished) {
new Thread(new Runnable() {
public void run() {
try {
URL url = new URL("http://web.mit.edu/");
HttpURLConnection connection = (HttpURLConnection) url.openConnection();
connection.setRequestMethod("GET");
connection.setConnectTimeout(5000);
isConnected = connection.getResponseCode() == HttpURLConnection.HTTP_OK;
} catch (Exception e) {
e.printStackTrace();
}
}
}).start();
if (isConnected == false){
alertDialog.setMessage("Try " + (5 - millisUntilFinished/1000) + " of 5.");
} else {
alertDialog.dismiss();
}
}
@Override
public void onFinish() {
if (isConnected == false) {
alertDialog.dismiss();
new AlertDialog.Builder(activity)
.setTitle("No Internet")
.setMessage("Please connect to Internet first.")
.setPositiveButton(android.R.string.yes, new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int which) {
// kill the app?
}
})
.setIcon(android.R.drawable.ic_dialog_alert)
.show();
} else {
// Launch the app
}
}
}.start();
